Methods of growing a group III nitride crystal

A method of growing a group III nitride crystal grows a group III nitride crystal from a solution in which an alkaline metal, a group III metal and nitrogen are dissolved, and includes, in the solution, a material which increases solubility of the nitrogen into the solution.

BACKGROUND OF THE INVENTION

The present invention generally relates to methods of growing group III nitride crystals, group III nitride crystals grown thereby, group III nitride crystal growing apparatuses and semiconductor devices, and more particularly to a method of growing a group III nitride crystal which is suited for use in semiconductor devices such as violet light sources which may be used for writing and/or reading information to and/or from optical disks, ultraviolet light sources such as laser diodes and light emitting diodes, violet light sources which may be used for electronic photography, and group III nitride electron devices. The present invention also relates to a group III nitride crystal and a semiconductor device which are produced using the method of growing the group III nitride crystal, and to a group III nitride crystal growing apparatus for growing such a group III nitride crystal.

Existing InGaAlN (group III nitride) devices which are used for violet, blue and green light sources are generally made by using crystal growing methods such as Metal Organic Chemical Vapor Deposition (MO-CVD) and Molecular Beam Epitaxy (MBE) to grow the InGaAlN (group III nitride) crystal on a sapphire or SiC substrate. But when the sapphire or SiC substrate is used, crystal defects increase due to large differences between the coefficient of thermal expansion and the lattice constant of the InGaAlN (group III nitride) crystal and the coefficient of thermal expansion and the lattice constant of the sapphire or SiC substrate. As a result, device performances of the semiconductor devices having the InGaAlN (group III nitride) grown on the sapphire or SiC substrate deteriorate, thereby making it difficult to extend the serviceable life of the light emitting devices, for example, and increasing the power required to operate such semiconductor devices.

Furthermore, in the case of the sapphire substrate which is insulative, it is impossible to draw out the electrodes via the substrate as done in the conventional light emitting devices. Consequently, when the sapphire substrate is used, the electrodes must be drawn out via the group III nitride crystal layer which is grown on the sapphire substrate. As a result, the device area becomes large and it becomes difficult to reduce the cost of such semiconductor devices.

In addition, in the case of the semiconductor device having the group III nitride crystal grown on the sapphire substrate, it is difficult to separate the chips by slicing, and it is not easy to obtain a resonator end surface required by the laser diode by cleavage. For this reason, existing techniques form the resonator end surface by dry etching or, polishes the sapphire substrate to a thickness of 100 μm or less before forming the resonator end surface by a process similar to cleavage. But according to these existing techniques, it is impossible to easily perform the formation of the resonator end surface and the chip separation in a single process as done in conventional laser diodes. Accordingly, these existing techniques require complex processes and increase the cost of the semiconductor devices.

In order to solve the problems described above, a technique was proposed to reduce the crystal defects by taking measures such as selectively growing the group III nitride crystal in a lateral direction on the sapphire substrate. According to this proposed technique, it is possible to reduce the crystal defects compared to a case where a GaN layer is not selectively grown in the lateral direction on the sapphire substrate. However, the above described problems associated with the insulation and the cleavage caused by the use of the sapphire substrate still exist. Furthermore, this proposed technique requires complex processes, and the sapphire substrate warps due to the growing of the GaN layer on the sapphire substrate since sapphire and GaN have different properties. As a result, the cost of the semiconductor device becomes high when this proposed technique is employed to make the semiconductor device.

In order to solve these problems, it is desirable to grow on the substrate a layer which is made of the same material as the substrate. In the case described above, it is desirable to grow the GaN layer on a GaN substrate. Hence, research is being made to grow the crystal of bulk GaN by vapor phase deposition, solution growth and the like. However, a GaN substrate having a practical size and a high quality has yet to be realized.

One method of realizing the GaN substrate is proposed in H. Yamane et al., “Preparation of GaN Single Crystals Using a Na Flux”, Chem. Mater. 1997, Vol. 9, pp. 413-416. This proposed method grows the GaN crystal using Na as flux. More particularly, this proposed method uses NaN3and Ga as raw materials, and seals the raw materials in a nitrogen atmosphere within a stainless steel reaction chamber which has an internal diameter of 7.5 mm and a length of 100 mm, for example. The GaN crystal is grown by maintaining the reaction chamber at a temperature of 600° C. to 800° C. for 24 hours to 100 hours.

In the case of the proposed method according to H. Yamane et al., the Ga crystal can be grown at a relatively low temperature of 600° C. to 800° C. In addition, the pressure within the reaction chamber is on the order of approximately 100 kg/cm2and is relatively low. Hence, the growth condition of this proposed method is practical.

However, the problem with this proposed method is that the size of the obtained crystal is on the order of approximately 1 mm or less and small. In other words, the reaction chamber used in H. Yamane et al. is a completely closed system, and the raw materials cannot be supplied from outside the reaction chamber. For this reason, the raw materials are depleted during the crystal growth and the crystal growth stops, thereby making the size of the obtained crystal on the order of approximately 1 mm and small. From the practical point of view, the crystal having such a small size is unsuited for making the semiconductor device.

In view of the above, first and second methods were respectively proposed in Japanese Laid-Open Patent Applications No. 2001-58900 and No. 2001-102316.

FIG. 1is a cross sectional view showing a crystal growing apparatus used by the first method. As shown inFIG. 1, a growth chamber102and a group III metal supply pipe103are provided within a reaction chamber101. External pressure is applied to the group III metal supply pipe103from outside the reaction chamber101, so as to additionally supply a group III metal104to the reaction chamber102which contains flux. In other words, in order to increase the size of the group III nitride crystal which is obtained, the first method additionally supplies the group III metal104when growing the group III nitride crystal.

The group III metal supply pipe103has a hole105. The crystal growing apparatus further includes a pressure applying unit106, an internal space107of the reaction chamber101, a nitrogen supply pipe108, a pressure control unit109, a lower heater110, and a side heater111.

On the other hand, the second method may be categorized into a mixing method and a fusion method. The mixing method applies external pressure to a molten mixture supply pipe which contains a molten mixture of flux (Na) and group III metal (Ga), so as to additionally supply the molten mixture to a growth chamber which contains the flux. The fusion method supplies an intermetallic compound of flux (Na) and group III metal (Ga), and additionally supplies the group III metal by partial fusion of the intermetallic compound.

According to the first and second methods described above, the raw materials are additionally supplied during the crystal growth, thereby making it possible to grow larger crystals.

However, according to the first method, vapor of the flux (Na) concentrates at a low-temperature portion, causing the flux (Na) to adhere on the group III metal supply pipe103which has a low temperature. As a result, the hole105of the group III metal supply pipe103may be clogged by the adhered flux (Na). If the temperature of the group III metal supply pipe103is increased in order to prevent the flux (Na) from adhering thereon, the group III metal reacts with the material forming the group III metal supply pipe103in a case where the group III metal is Ga and the material forming the group III metal supply pipe103is stainless steel, for example. Consequently, the hole105of the group III metal supply pipe103is also clogged when such a reaction occurs between the group III metal and the material forming the group III metal supply pipe103.

On the other hand, according to the mixing method of the second method, the flux exists within the molten mixture supply pipe. For this reason, the group III metal and the nitrogen react within the molten mixture supply pipe and generate a group III nitride, to thereby clog the molten mixture supply pipe.

According to the fusion method of the second method, if the intermetallic compound is mixed into the flux and partially fused, a rapid reaction occurs between the intermetallic compound and the nitrogen, to thereby deteriorate the crystal properties of the group III nitride which is obtained.

And, according to the mixing and fusion methods of the second method, the solubility of the nitrogen to the molten mixture is small, and the growth rate of the group III nitride crystal is low.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to provide a novel and useful method of growing a group III nitride crystal, group III nitride crystal grown thereby, a group III nitride crystal growing apparatus and semiconductor device, in which the problems described above are eliminated.

Another and more specific object of the present invention is to provide a method of growing a group III nitride crystal, capable of growing a high-quality group III nitride crystal having a practically large size, a group III nitride crystal grown thereby, a group III nitride crystal growing apparatus, and a semiconductor device which includes a layer of such a group III nitride crystal.

Still another and more specific object of the present invention is to provide a method of growing a group III nitride crystal, comprising growing a group III nitride crystal from a solution in which an alkaline metal, a group III metal and nitrogen are dissolved; and including, in the solution, a material which increases solubility of the nitrogen into the solution.

Another object of the present invention is to provide a method of growing a group III nitride crystal, comprising preparing, as a solvent, a solution which includes an alkaline metal; and growing a group III nitride crystal by fusing a group III nitride into the solution and recrystallizing the group III nitride.

A further object of the present invention is to provide a group III nitride crystal grown by a process comprising growing a group III nitride crystal from a solution in which an alkaline metal, a group III metal and nitrogen are dissolved; and including, in the solution, a material which increases solubility of the nitrogen into the solution, wherein the group III nitride crystal is plate-shaped or columnar.

Another object of the present invention is to provide a group III nitride crystal growing apparatus comprising a reaction chamber; and a solution container, provided within the reaction chamber, to contain a solution in which an alkaline metal, a group III metal and nitrogen are dissolved, the solution including a material which increases solubility of the nitrogen into the solution, whereby a group III nitride crystal is grown in the solution within the solution container.

Still another object of the present invention is to provide a method of growing a group III nitride crystal, comprising growing a group III nitride crystal from a solution in which an alkaline metal, a group III metal and nitrogen are dissolved; and including, in the solution, a material which controls a ratio of a growth rate of the group III nitride crystal in a first direction approximately parallel to a c-axis thereof and a growth rate of the group III nitride crystal in a second direction approximately perpendicular to the c-axis direction thereof.

A further object of the present invention is to provide a method of growing a group III nitride crystal, comprising growing a group III nitride crystal from a solution in which an alkaline metal, a group III metal and nitrogen are dissolved; and including, in the solution, Li which controls a ratio of a growth rate of the group III nitride crystal in a first direction approximately parallel to a c-axis thereof and a growth rate of the group III nitride crystal in a second direction approximately perpendicular to the c-axis direction thereof.

Another object of the present invention is to provide a group III nitride crystal grown by a process comprising growing a group III nitride crystal from a solution in which an alkaline metal, a group III metal and nitrogen are dissolved; and including, in the solution, a material which controls a ratio of a growth rate of the group III nitride crystal in a first direction approximately parallel to a c-axis thereof and a growth rate of the group III nitride crystal in a second direction approximately perpendicular to the c-axis direction thereof, wherein the group III nitride crystal is plate-shaped or columnar depending on the material.

Still another object of the present invention is to provide a group III nitride crystal growing apparatus comprising a reaction chamber; and a solution container, provided within the reaction chamber, to contain a solution in which an alkaline metal, a group III metal and nitrogen are dissolved, the solution including a material which controls a ratio of a growth rate of the group III nitride crystal in a first direction approximately parallel to a c-axis thereof and a growth rate of the group III nitride crystal in a second direction approximately perpendicular to the c-axis direction thereof, whereby a group III nitride crystal is grown in the solution within the solution container.

A further object of the present invention is to provide a method of growing a group III nitride crystal, comprising fusing a group III nitride into a solution including an alkaline metal; and recrystallizing a group III nitride crystal at a location different from a location where the group III nitride is dissolved within the solution.

Another object of the present invention is to provide a group III nitride crystal grown by a process comprising fusing a group III nitride into a solution including an alkaline metal; and recrystallizing a group III nitride crystal at a location different from a location where the group III nitride is dissolved within the solution.

Still another object of the present invention is to provide a group III nitride crystal growing apparatus, comprising a reaction chamber; and a solution container, provided in the reaction chamber, to contain a group III nitride which is dissolved into a solution including an alkaline metal, whereby a group III nitride crystal is recrystallized at a location within the solution chamber different from a location where the group III nitride is dissolved within the solution.

A further object of the present invention is to provide a method of growing a group III nitride crystal, comprising forming, within a reaction chamber, a molten mixture of an alkaline metal and a material which includes a group III metal; growing a group III nitride crystal which is made of the group III metal and nitrogen, from the molten mixture and a material which includes the nitrogen; and controlling a temperature in a vicinity of a surface of the molten mixture and a temperature of a crystal growing region within the molten mixture, so that the nitrogen dissolves into the molten mixture from the surface and the group III nitride crystal grows in the crystal growing region which is other than the surface.

Another object of the present invention is to provide a group III nitride crystal grown by a process comprising forming, within a reaction chamber, a molten mixture of an alkaline metal and a material which includes a group III metal; growing a group III nitride crystal which is made of the group III metal and nitrogen, from the molten mixture and a material which includes the nitrogen; and controlling a temperature in a vicinity of a surface of the molten mixture and a temperature of a crystal growing region within the molten mixture, so that the nitrogen dissolves into the molten mixture from the surface and the group III nitride crystal grows in the crystal growing region which is other than the surface.

Still another object of the present invention is to provide a group III nitride crystal growing apparatus comprising a reaction chamber; a solution container, provided within the reaction chamber, to contain a molten mixture of an alkaline metal and a material which includes a group III metal, so that a group III nitride crystal which is made of the group III metal and nitrogen is grown from the molten mixture and a material which includes the nitrogen; and means for controlling a temperature in a vicinity of a surface of the molten mixture and a temperature of a crystal growing region within the molten mixture, so that the nitrogen dissolves into the molten mixture from the surface and the group III nitride crystal grows in the crystal growing region which is other than the surface.

A further object of the present invention is to provide a semiconductor device comprising a substrate made of a group III nitride; and a stacked structure provided on the substrate, where the stacked structure is selected from a group consisting of a light emitting structure, a light receiving structure and a transistor structure, and the substrate is made by any of the above described methods of growing a group III nitride crystal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will be given of various embodiments of a method of growing a group III nitride crystal, a group III nitride crystal grown thereby, a group III nitride crystal growing apparatus, and a semiconductor device, according to the present invention, by referring toFIG. 2and the subsequent figures.

First Embodiment

According to a first embodiment, Na is used as an alkaline metal, and Ga is used as a group III metal raw material. Nitrogen gas is used as nitrogen raw material, and Li is added using Li3N as a raw material, to grow GaN crystals as a group III nitride.

The Na, Ga and Li3N may be prepared in advance as a molten mixture within a solution container, and the nitrogen may be supplied during the crystal growth by fusion from a vapor phase into the molten mixture, to grow the GaN crystals.

FIG. 2is a cross sectional view showing a first embodiment of the group III nitride crystal growing apparatus, andFIG. 3is a perspective view showing a plate-shaped GaN crystal, that is, a first embodiment of the group III nitride crystal, which is obtained by growing the GaN crystal by the group III nitride crystal growing apparatus shown inFIG. 2.

The group III nitride crystal growing apparatus shown inFIG. 2includes a reaction chamber11which accommodates a solution container12. The reaction chamber11is made of stainless steel and has a closed shape. A solution25including the alkaline metal and the group III metal is contained within the solution container12. The solution container12is placed on a holder26, and contains the solution25which is required for the crystal growth of the GaN.

The solution container12may be removed from the reaction chamber11. In this embodiment, the solution container12is made of BN.

A gas supply pipe14connects to the reaction chamber11. The gas supply pipe14supplies nitrogen (N2) gas to an internal space23within the reaction chamber11, as the nitrogen raw material, and enables adjustment of the nitrogen (N2) gas pressure within the reaction chamber11from a pressure control unit16which connects to a N2gas supply pipe17.

The gas supply pipe14branches via a valve18so that Ar gas may be introduced. The Ar gas pressure may be adjusted from a pressure control unit19which connects to an Ar gas supply pipe20.

The total pressure within the reaction chamber11is monitored by a pressure gage22. A heater13is arranged on an outer side of the reaction chamber11. Valves15and21are provided in the gas supply pipe14. The reaction chamber11may be removed from the group III nitride crystal growing apparatus at the valve21, so that only the reaction chamber11may be placed into a glove box and worked on by an operator.

Next, a description will be given of a first embodiment of the method of growing the group III nitride crystal according to the present invention, which grows GaN, by the group III nitride crystal growing apparatus shown inFIG. 2.

First, the reaction chamber11is separated from the group III nitride crystal growing apparatus at the valve21, and placed into a glove box (not shown) having an Ar atmosphere.

Then, Ga is supplied as the group III metal raw material and Na is supplied as the alkaline metal, into the solution container12which is made of BN. A proportion of Na in the solution25is set to Na/(Na+Ga)=0.7.

In addition, Li3N is supplied as the Li raw material, into the solution container12.

Next, the solution container12is placed on the holder26and set within the reaction chamber11. The reaction chamber11is sealed, the valve21is closed, and the inside of the reaction chamber11is shut off from the external atmosphere. The reaction chamber11is then removed from the glove box, and assembled into the group III nitride crystal growing apparatus. In other words, the reaction chamber11is set at a predetermined position of the group III nitride crystal growing apparatus where the heater13is provided, and is connected to the gas supply pipe14at the valve21so that the reaction chamber11may receive the N2and Ar gases.

The valves15and21are then opened, to supply the N2gas into the reaction chamber11. In this state, the N2gas pressure is set to 3.3 MPa by the pressure control unit16. In this embodiment, this N2gas pressure of 3.3 MPa causes the total pressure within the reaction chamber11to become 4 MPa when the temperature within the reaction chamber11rises to a crystal growth temperature of 775° C., for example.

Then, the valve15is closed, and the valve18is opened, to supply the Ar gas into the reaction chamber11. In this state, the Ar gas pressure is set to 6.6 MPa by the pressure control unit19. In other words, the Ar partial pressure within the reaction chamber11becomes 3.3 MPa. In this embodiment, this Ar gas pressure of 6.6 MPa causes the total pressure within the reaction chamber11to become 8 MPa when the temperature within the reaction chamber11rises to a crystal growth temperature of 775° C., for example. That is, this Ar gas pressure of 6.6 MPa causes the N2partial pressure and the Ar partial pressure within the reaction chamber11to become 4 MPa, respectively.

Thereafter, the valves18and21are closed. As a result, the reaction chamber11is sealed. Then, the heater13is turned ON, to raise the temperature of the reaction chamber11and thus the temperature of the solution25from room temperature of 27° C. to the crystal growth temperature of 775° C. in 1 hour.

As the temperature of the reaction chamber11rises, the pressure within the sealed reaction chamber11increases, and the total pressure within the reaction chamber11becomes 8 MPa when the crystal growth temperature of 775° C. is reached. In other words, the N2partial pressure and the Ar partial pressure within the reaction chamber11respectively become 4 MPa.

This state is maintained for 200 hours, before lowering the temperature to the room temperature. When the reaction chamber11was opened after the end of the crystal growing process, the present inventors found that virtually all of the Ga reacted with the nitrogen, and a large number of colorless transparent plate-shaped GaN microcrystals29were grown on the inner walls of the solution container12. In addition, the present inventors found that a plate-shaped GaN crystal30shown inFIG. 3having a diameter of approximately 5 mm was grown on the surface of the solution25. The thickness of the plate-shaped GaN crystal30was approximately 80 μm or greater. Furthermore, a halfwidth of an X-ray rocking curve with respect to the plate-shaped GaN crystal30was approximately 45 arcsec to approximately 55 arcsec and narrow, and the defect density was approximately 106cm−2or less by the etch pit density evaluation. Moreover, the plate-shaped GaN crystal30had a high resistance and was semiinsulative.

On the other hand, when a similar crystal growing process was performed without supplying the Li3N into the solution25, the present inventors found that there remained Ga which did not react with the N2. In addition, the present inventors found that a small columnar GaN crystal and a large number of thin plate-shaped GaN microcrystals having the c-plane as the principal plane were grown on the inner walls of the solution container12. Moreover, a GaN crystal having a diameter of approximately 3 mm was grown at the surface of the solution25. When Li was mixed into the solution25, it was found that only a plate-shaped GaN crystal grows and the growth rate of the GaN crystal is high, thereby enabling a larger GaN crystal to be grown within a shorter time.

Therefore, this embodiment of the method of growing a group III nitride crystal includes growing a group III nitride crystal from a solution in which an alkaline metal, a group III metal and nitrogen are dissolved, and including, in the solution, a material which increases solubility of the nitrogen into the solution. The material may be selected from a group consisting of Li, Ca and alkaline earth metals. When the material is Li, the Li may be included in the solution by adding a nitrogen compound to the solution.

For example, an intermetallic compound of Li and the group III metal fuses at the crystal growing temperature, and will not interfere with the crystal growth. Hence, it is possible to grow a larger group III nitride crystal compared to the conventional method, when the same amount of solution is used.

When the nitrogen compound is used as the Li raw material, it is possible to reduce the weighing error. In other words, a large weighing error may occur when weighing the Li because the mass number of Li is small, but it is possible to reduce the weighing error by using the nitride compound. In addition, no impurity elements will mix into the solution when the nitrogen compound is used, thereby making it possible to grow a high-quality group III nitride crystal.

Accordingly, the group III metal and the nitrogen react within the solution, and the group III nitride crystal of the group III metal and the nitride is grown. By including, in the solution, the material which increases the solubility of the nitrogen into the solution, the group III nitride crystal grows within the solution having a high nitrogen concentration compared to the case where the above material is not dissolved in the solution. For this reason, it is possible to prevent the lack of nitrogen supply which was one cause of the slow growth rate, and accordingly, increase the growth rate. In addition, it is possible to reduce the nitrogen defect caused by the lack of nitrogen supply, and thus grow the group III nitride crystal having a high quality and substantially reduced defects.

The group III nitride may by any suitable compound of nitrogen and one or more group III metals, such as Ga, Al, In and B. In addition, the alkaline metal may be any suitable alkaline metal including Na and K.

The group III metal raw material is not limited to a particular group III material, and any suitable group III material may be used, including group III metals, group III nitrides and materials formed by group III elements. Furthermore, the nitrogen raw material Is not limited to a particular nitrogen material, and any suitable material including nitrogen may be used. Moreover, the nitrogen compound may be dissolved into the solution or, the nitrogen compound gas may be dissolved into the solution in the vapor state.

Second Embodiment

According to a second embodiment, Na is used as a solvent including an alkaline metal, and GaN is used as a group III nitride raw material. The GaN raw material is dissolved into the Na solvent, to grow GaN crystals as a group III nitride at a bottom of a solution container.

FIG. 4is a cross sectional view showing a second embodiment of the group III nitride crystal growing apparatus. InFIG. 4, those parts which are the same as those corresponding parts inFIG. 2are designated by the same reference numerals, and a description thereof will be omitted.

The structure of the group III nitride crystal growing apparatus shown inFIG. 4is basically the same as that of the group III nitride crystal growing apparatus shown inFIG. 2, except for the shape of the solution container12, the provision of a raw material container24which is located at an upper part of the solution container12to contain a GaN raw material31, and the provision of a cooling rod27at a bottom portion of the solution container12.

According to the group III nitride crystal growing apparatus shown inFIG. 4, it is possible to locally set the bottom of the solution container12to a low temperature, by the cooling rod27which is provided at the bottom portion of the solution container12.

Next, a description will be given of a second embodiment of the method of growing the group III nitride crystal according to the present invention, which grows GaN, by the group III nitride crystal growing apparatus shown inFIG. 4.

First, the reaction chamber11is separated from the group III nitride crystal growing apparatus at the valve21, and placed into a glove box (not shown) having an Ar atmosphere.

Then, the GaN raw material and the Na solvent are supplied to the solution container12which is made of BN. The solution container12is placed on the holder26and set within the reaction chamber11. The reaction chamber11is sealed, the valve21is closed, and the inside of the reaction chamber11is shut off from the external atmosphere. The reaction chamber11is then removed from the glove box, and assembled into the group III nitride crystal growing apparatus.

In other words, the reaction chamber11is set at a predetermined position of the group III nitride crystal growing apparatus where the heater13is provided, and is connected to the gas supply pipe14at the valve21so that the reaction chamber11may receive the N2and Ar gases. Thereafter, the N2gas is supplied to the reaction chamber11so as to prevent the nitrogen from escaping the solution25into the vapor phase.

In addition, the Ar gas is supplied to the reaction chamber11so as to suppress evaporation of the Na, and the pressure within the reaction chamber11is increased.

In this embodiment, the pressure within the reaction chamber11is set to 8 MPa, and the partial pressures of the N2and Ar gases respectively are 4 MPa. Then, the heater13is turned ON to raise the temperature of the reaction chamber11to 800° C. The GaN crystal is grown by maintaining the temperature of the reaction chamber11at 800° C. for 300 hours, and the temperature of the reaction chamber11is thereafter reduced to the room temperature. While the temperature of the reaction chamber11is maintained at 800° C., the GaN raw material31gradually dissolves, and is recrystallized at the bottom of the solution container12where the temperature is low, to thereby grow the GaN crystal. When the reaction chamber11was opened after the end of the crystal growing process, it was found that the GaN raw material31slightly remains, and a columnar colorless transparent GaN crystal32having a length of approximately 3 mm and a large number of GaN microcrystals29were grown at the bottom of the solution container12.

Therefore, this embodiment of the method of growing the group III nitride crystal grows the group III nitride crystal by dissolving a group III nitride into a solvent which includes the alkaline metal and recrystallizing the group III nitride. In other words, unlike the conventional method, the group III nitride is used as the raw material, and the group III nitride is dissolved and recrystallized within the solvent.

Hence, the raw material required for the crystal growth is stably supplied, and a practically large group III nitride crystal having a high quality can be grown.

Conventionally, no suitable solvent existed that dissolved the group III nitride with a solubility required for the crystal growth. But by using the solvent including the alkaline metal, it is possible to dissolve the group III nitride with the solubility required for the crystal growth, and to recrystallize the group III nitride to grow the group III nitride crystal.

Na, K and the like may be used for the alkaline metal included in the solvent or used as the solvent. However, the alkaline metal of the solvent is not limited to such, and any suitable material may be used depending on the group III nitride to be dissolved. For example, when fusing GaN as the group III nitride, Na may be used as a suitable alkaline metal for the solvent.

The method of recrystallization is also not limited to a particular method. For example, a temperature difference may be generated in the solution, so as to dissolve the group III nitride at the high temperature portion of the solution and to recrystallize the group III nitride at the low temperature portion of the solution. Alternatively, it is possible to reduce the temperature of the solution in which the group III nitride is dissolved by an amount greater than or equal to the saturated concentration, so as to cause the recrystallization of the group III nitride. Furthermore, the solvent may be evaporated so as to supersaturate the solvent concentration, so as to cause the recrystallization of the group III nitride.

In order to prevent the nitrogen defect, it is possible to supply the nitrogen into the solution by use a nitrogen raw material, separately from the nitrogen obtained by the dissolving of the group III nitride.

Third Embodiment

According to a third embodiment, Na is used as a solvent including an alkaline metal, and GaN is used as a group III nitride raw material. The GaN raw material is dissolved into the Na solvent, and the Na solvent is evaporated to form a saturated solution, so as to segregate the supersaturated GaN and grow GaN crystals as a group III nitride.

FIG. 5is a cross sectional view showing a third embodiment of the group III nitride crystal growing apparatus. InFIG. 5, those parts which are the same as those corresponding parts inFIG. 2are designated by the same reference numerals, and a description thereof will be omitted. The structure of the group III nitride crystal growing apparatus shown inFIG. 5is basically the same as that of the group III nitride crystal growing apparatus shown inFIG. 2.

Next, a description will be given of a third embodiment of the method of growing the group III nitride crystal according to the present invention, which grows GaN, by the group III nitride crystal growing apparatus shown inFIG. 5.

The GaN raw material and the Na solvent are supplied to the solution container12and heated to 800° C. so as to dissolve the GaN raw material. The N2gas is supplied to the reaction chamber11so as to prevent the nitrogen from escaping the solution25into the vapor phase, and the N2gas is used to set the pressure within the reaction chamber11to 4 MPa.

The reaction chamber11is maintained at 800° C. for 400 hours to evaporate the Na solvent. As the Na solvent evaporates, the solution25reaches a supersaturated state, and the supersaturated GaN is segregated to grow the GaN crystals. When the reaction chamber11was opened after the end of the crystal growing process, it was found that the Na solvent is reduced, and a columnar colorless transparent GaN crystal33having a length of approximately 3 mm and a large number of GaN microcrystals29were grown at the bottom of the solution container12.

Therefore, this embodiment of the method of growing the group III nitride crystal includes setting a concentration of the group III nitride within the solution to become greater than or equal to a saturated concentration, so as to segregate the group III nitride and grow the group III nitride crystal. In other words, the crystal segregation occurs and the crystal growth can be started when the dissolved concentration of the group III nitride within the solution becomes greater than or equal to the saturated concentration.

The method of making the group III nitride concentration within the solution to become greater than or equal to the saturated concentration is not limited to a particular method. For example, the temperature of the solution may be reduced, so that the group III nitride concentration becomes greater than or equal to the saturated concentration. Alternatively, differences in the solubilities of the group III nitride caused by the temperature of the solution may be effectively utilized to grow the group III nitride crystal.

Fourth Embodiment

According to a fourth embodiment, Na is used as an alkaline metal, and GaN is used as a group III nitride raw material. The GaN raw material is dissolved into the Na solution, and the solution temperature is gradually reduced to form a saturated solution, so as to segregate the supersaturated GaN and grow GaN crystals as a group III nitride.

FIG. 6is a cross sectional view showing a fourth embodiment of the group III nitride crystal growing apparatus. InFIG. 6, those parts which are the same as those corresponding parts inFIG. 2are designated by the same reference numerals, and a description thereof will be omitted. The structure of the group III nitride crystal growing apparatus shown inFIG. 6is basically the same as that of the group III nitride crystal growing apparatus shown inFIG. 2.

Next, a description will be given of a fourth embodiment of the method of growing the group III nitride crystal according to the present invention, which grows GaN, by the group III nitride crystal growing apparatus shown inFIG. 6.

The GaN raw material and the Na are supplied to the solution container12and heated, so as to dissolve the GaN raw material.

FIG. 7is a diagram showing an amount of dissolved GaN within 1 g of Na with respect to the temperature of the molten mixture, obtained from experiments conducted by the present inventors. InFIG. 7, the ordinate indicates the amount of dissolved GaN in mg, and the abscissa indicates the temperature in ° C. In addition, a curve I shows a case where no Li is added as in the case of this embodiment, and a curve II shows a case where Li is added as in the case of a fifth embodiment which will be described later.

It may be seen fromFIG. 7that the amount of dissolved GaN increases sharply when the temperature becomes 750° C. or greater. In this embodiment, 15 g of Na is supplied to the solution container12, and 270 mg of GaN raw material is supplied to the solution container12. The solution container12is then heated to 800° C. to dissolve the GaN raw material and form a saturated solution. The present inventors have found through experiments that the reaction of the dissolved GaN reaches an equilibrium state in 50 hours to 100 hours. In this embodiment, the solution container12is maintained at 800° C. for 50 hours to dissolve the GaN raw material. Thereafter, the solution container12is cooled from 800° C. to 700° C. at a cooling rate of 1° C./hour.

The N2gas is supplied to the internal space23within the reaction chamber11so as to prevent the nitrogen from escaping the solution25into the vapor phase. In addition, the Ar gas is supplied to the internal space23within the reaction chamber11so as to suppress evaporation of the Na, and the pressure within the reaction chamber11is increased. The pressure within the reaction chamber11is set to 8 MPa, and the partial pressures of the N2and Ar gases respectively are 4 MPa.

As the temperature of the solution25falls, the solution25reaches a supersaturated state, and the supersaturated GaN is segregated to grow GaN crystals. When the reaction chamber11was opened after the end of the crystal growing process, a colorless transparent GaN crystal34having a size of approximately 2 mm and a large number of GaN microcrystals29were grown at the bottom of the solution container12.

Therefore, this embodiment of the method of growing the group III nitride sets the concentration of the group III nitride within the solution to become greater than or equal to the saturated concentration by decreasing a temperature of the solution. In other words, since the solubility of the group III nitride decreases when the temperature of the alkaline metal decreases, the solution reaches the supersaturated state as the temperature of the solution decreases, to cause segregation of the group III nitride. Hence, the differences in the solubilities of the group III nitride caused by the temperature of the solution are effectively utilized to grow the group III nitride crystal.

Accordingly, the crystal growth rate can be controlled by the temperature falling rate of the solution, to thereby control the crystal quality. As a result, it is possible to grow a high-quality group III nitride crystal.

Fifth Embodiment

According to the fifth embodiment, Na is used as an alkaline metal, and GaN is used as a group III nitride raw material. Furthermore, Li3N is dissolved as a raw material into the solution of Na and GaN, so as to add Li which increases the solubility of nitrogen in the solution, that is, increases the solubility of GaN. The GaN raw material is dissolved into the Na solution, and the solution temperature is gradually reduced to form a saturated solution, so as to segregate the supersaturated GaN and grow GaN crystals as a group III nitride.

In other words, this embodiment is similar to the fourth embodiment described above, except that Li is dissolved into the solution.

A fifth embodiment of the group III nitride crystal growing apparatus has the same structure as the fourth embodiment of the group III nitride crystal growing apparatus shown inFIG. 6.

Next, a description will be given of a fifth embodiment of the method of growing the group III nitride crystal according to the present invention, which grows GaN, by the group III nitride crystal growing apparatus shown inFIG. 6.

This fifth embodiment of the method is basically the same as the fourth embodiment of the method described above, except that Li3N is dissolved into the solution25so as to add Li to the solution25. The addition of Li increases the solubility of the nitrogen, that is, increases the solubility of the GaN. Hence, a larger amount of the GaN raw material is supplied compared to the fourth embodiment which does not add Li.

InFIG. 7, the curve II shows the amount of dissolved GaN within 1 g of Na with respect to the temperature of the molten mixture, for a case where 0.1 mmol of Li3N is dissolved into the molten mixture to add the Li. On the other hand, the curve I shows the amount of dissolved GaN within 1 g of Na with respect to the temperature of the molten mixture, for the case where no Li is added.

In this fifth embodiment, 15 g of Na, 1.5 mmol of Li3N and 375 mg of GaN raw material are supplied to the solution container12, and maintained at 800° C. for 50 hours to dissolve the GaN raw material and form a saturated solution. Thereafter, the solution container12is cooled from 800° C. to 700° C. at a cooling rate of 1° C./hour.

The N2gas is supplied to the internal space23within the reaction chamber11so as to prevent the nitrogen from escaping the solution25into the vapor phase. In addition, the Ar gas is supplied to the internal space23within the reaction chamber11so as to suppress evaporation of the Na, and the pressure within the reaction chamber11is increased. The pressure within the reaction chamber11is set to 8 MPa, and the partial pressures of the N2and Ar gases respectively are 4 MPa.

As the temperature of the solution25falls, the solution25reaches a supersaturated state, and the supersaturated GaN is segregated to grow GaN crystals. When the reaction chamber11was opened after the end of the crystal growing process, a colorless transparent GaN crystal34having a size of approximately 3 mm and a large number of GaN microcrystals29were grown at the bottom of the solution container12. Compared to the case where no Li is added to the solution25, the amount of GaN crystal grown increases by an amount corresponding to a difference between the solubilities of GaN for the case where Li is added and the case where no Li is added, to simultaneously increase the GaN crystal size.

Therefore, this embodiment of the method of growing the group III nitride selects the material from a group consisting of alkaline metals other than the alkaline metal included in the solvent. In other words, the material which increases the solubility of the nitrogen into the solution, increases the solubility of the group III nitride into the solution. Any suitable material which does not interfere with the crystal growth may be used for this material which increases the solubility of the nitrogen into the solution. The material may be selected from a group consisting of Li, Ca and alkaline earth metals. In addition, when the material is Li, the Li may be included in the solution by adding a nitrogen compound to the solution.

Accordingly, it is possible to increase the nitrogen concentration within the solution compared to the conventional method, and increase the solubility of the group III nitride. Consequently, a larger group III nitride crystal may be grown compared to the conventional method, using the same amount of solution. In addition, since the nitrogen concentration within the solution is increased, it is possible to suppress the lack of nitrogen supply and accordingly, reduce defects such as nitrogen defects. As a result, it is possible to grow a high-quality group III nitride crystal.

Sixth Embodiment

A sixth embodiment is similar to the fifth embodiment described above, except that a seed crystal is used to grow the crystals. In other words, Na is used as an alkaline metal, GaN is used as a group III nitride raw material, and Li3N is dissolved as a raw material into the solution of Na and GaN so as to add Li which increases the solubility of nitrogen in the solution, that is, increases the solubility of GaN. The GaN raw material is dissolved into the Na solution, and the solution temperature is gradually reduced to form a saturated solution, so as to segregate the supersaturated GaN and grow GaN crystals as a group III nitride.

FIG. 8is a cross sectional view showing a sixth embodiment of the group III nitride crystal growing apparatus. InFIG. 8, those parts which are the same as those corresponding parts inFIG. 2are designated by the same reference numerals, and a description thereof will be omitted. The structure of the group III nitride crystal growing apparatus shown inFIG. 8is basically the same as that of the group III nitride crystal growing apparatus shown inFIG. 2, except that a mechanism is provided to hold the seed crystal.

Next, a description will be given of a sixth embodiment of the method of growing the group III nitride crystal according to the present invention, which grows GaN, by the group III nitride crystal growing apparatus shown inFIG. 8.

This embodiment grows the GaN crystal in a manner similar to the fifth embodiment described above, except that a seed crystal35is immersed in a vicinity of the surface of the solution25so as to grow the GaN crystal thereat.

The GaN raw material which is dissolved into the solution25is drawn towards the surface of the seed crystal35, and the GaN crystal preferentially grows on the seed crystal35. The solution container12is cooled from 800° C. to 700° C. at a cooling rate of 1° C./hour. When the reaction chamber11was opened after the end of the crystal growing process, a colorless transparent GaN single crystal36having a length of approximately 5 mm was grown on the seed crystal35. The GaN crystal36which is grown on the seed crystal35had a larger crystal size compared to the case where no seed crystal is used.

Therefore, this embodiment of the method of growing the group III nitride crystal selects the material from a group consisting of Li, Ca and alkaline earth metals. When the material is Li, the Li may be included in the solution by adding a nitrogen compound to the solution. Further, the group III nitride crystal may be grown on a seed crystal.

Hence, it is possible to selectively grow the group III nitride crystal on the seed crystal, and a practically large group III nitride crystal having a high quality can be grown at a desired position. Moreover, it is possible to control the crystal orientation of the group III nitride crystal which is grown, because the seed crystal is used. In other words, it is possible to grow a group III nitride crystal having a desired crystal face.

Seventh Embodiment

According to a seventh embodiment, Na is used as an alkaline metal, and GaN is used as a group III nitride raw material. Furthermore, Li3N is dissolved as a raw material into the solution of Na and GaN, so as to add Li which increases the solubility of nitrogen in the solution, that is, increases the solubility of GaN. The GaN raw material is dissolved into the Na solution at a high temperature portion, and the GaN is segregated on a seed crystal at a low temperature portion to grow the GaN crystals as a group III nitride.

FIG. 9Ais a cross sectional view showing a seventh embodiment of the group III nitride crystal growing apparatus, andFIG. 9Bis a diagram showing a temperature distribution within a reaction chamber of the group III nitride crystal growing apparatus shown inFIG. 9Aalong a vertical direction. InFIG. 9B, the ordinate indicates the distance along the vertical direction of the reaction chamber in arbitrary units, and the abscissa indicates the temperature in arbitrary units.

The group III nitride crystal growing apparatus shown inFIG. 9Aincludes a reaction chamber41which accommodates a solution container42. The reaction chamber41is made of stainless steel and has a closed shape. A solution59including the alkaline metal is contained within the solution container42. The solution container42contains the solution59which is required for the crystal growth of the GaN.

The solution container42may be removed from the reaction chamber41. In this embodiment, the solution container42is made of BN.

A gas supply pipe49connects to the reaction chamber41. The gas supply pipe49supplies N2gas to an internal space45within the reaction chamber41, as the nitrogen raw material, and enables adjustment of the N2gas pressure within the reaction chamber41from a pressure control unit53.

The gas supply pipe49branches via a valve55so that Ar gas may be introduced to suppress evaporation of the alkaline metal. The Ar gas pressure may be adjusted from a pressure control unit56.

The Ar gas is mixed as an inert gas to suppress the evaporation of the alkaline metal and to independently control the pressure of the N2gas. Hence, it is possible to perform the crystal growing process with a high controllability.

The total pressure within the reaction chamber41is monitored by a pressure gage51. An upper heater43and a lower heater44are arranged on an outer side of the reaction chamber41. Each of the upper and lower heaters43and44can be controlled to a desired temperature. Valves52and50are provided in the gas supply pipe49. The reaction chamber41may be removed from the group III nitride crystal growing apparatus at the valve50, so that only the reaction chamber41may be placed into a glove box and worked on by an operator.

A buffer46is provided within the solution container42, in order to suppress convection of the solution59and to generate a temperature gradient.

Next, a description will be given of a seventh embodiment of the method of growing the group III nitride crystal according to the present invention, which grows GaN, by the group III nitride crystal growing apparatus shown inFIG. 9A.

First, the reaction chamber41is separated from the group III nitride crystal growing apparatus at the valve50, and placed into a glove box (not shown) having an Ar atmosphere.

Then, GaN is supplied as the group III nitride raw material, Na is supplied as the alkaline metal, and Li3N is supplied, into the solution container42which is made of BN. The Na within the solution container42is fused, and a GaN seed crystal48which hangs from an upper portion of the solution container42is held at a predetermined position within the solution59.

Next, the solution container42is set within the reaction chamber41. The reaction chamber41is sealed, the valve50is closed, and the inside of the reaction chamber41is shut off from the external atmosphere.

Since the series of operations are carried out within the glove box under the Ar gas atmosphere, the inside of the reaction chamber41is filled with the Ar gas. The reaction chamber41is then removed from the glove box, and assembled into the group III nitride crystal growing apparatus. In other words, the reaction chamber41is set at a predetermined position of the group III nitride crystal growing apparatus where the upper and lower heaters43and44are provided, and is connected to the gas supply pipe49at the valve50so that the reaction chamber41may receive the N2and Ar gases. Then, the upper and lower heaters43and44are turned ON, to raise the temperature of the reaction chamber41and thus the temperature of the solution59, to a predetermined crystal growing temperature.

The lower heater44is set to a dissolving temperature of a GaN raw material47. On the other hand, the upper heater43is set to a temperature which is lower than that at a portion where the GaN raw material47exists. More particularly, the upper heater43is set to a crystal growing temperature at which the GaN seed crystal48grows. In this embodiment, the portion where the GaN raw material47exists is set to 850° C., and the portion where the GaN seed crystal48grows is set to 775° C.

The valves50and55are then opened, to supply the Ar gas from an Ar gas supply pipe57to the reaction chamber41via the gas supply pipe49. The pressure within the reaction chamber41is adjusted by the pressure control unit56, and the valve55is closed after setting the total pressure within the reaction chamber41to 4 MPa.

Thereafter, the valve52is opened, to supply the N2gas from a N2gas supply pipe54to the reaction chamber41via the gas supply pipe49. The pressure within the reaction chamber41is adjusted by the pressure control unit53, so that the total pressure within the reaction chamber41is 8 MPa. In other words, the N2partial pressure within the internal space45of the reaction chamber41is 4 MPa.

This state is maintained for 400 hours to carry out the crystal growing process, and the temperature of the reaction chamber41is then reduced to the room temperature. When the reaction chamber41was opened after reducing the gas pressure within the reaction chamber41, it was found that a colorless transparent GaN single crystal58having a length of approximately 10 mm was grown on the seed crystal48.

Therefore, this embodiment of the method of growing the group III nitride crystal also selects the material from a group consisting of Li, Ca and alkaline earth metals. When the material is Li, the Li may be included in the solution by adding a nitrogen compound to the solution. Further, the group III nitride crystal may be grown on a seed crystal.

Hence, it is possible to selectively grow the group III nitride crystal on the seed crystal, and a practically large group III nitride crystal having a high quality can be grown at a desired position. Moreover, it is possible to control the crystal orientation of the group III nitride crystal which is grown, because the seed crystal is used. In other words, it is possible to grow a group III nitride crystal having a desired crystal face.

Eighth Embodiment

According to an eighth embodiment, Na is used as an alkaline metal, and Ga is used as a group III metal raw material. Nitrogen gas is used as nitrogen raw material, and Li is added using Li3N as a raw material, to grow GaN crystals as a group III nitride.

The Na, Ga and Li3N may be prepared in advance as a molten mixture within a solution container, and the nitrogen may be supplied during the crystal growth by fusion from a vapor phase into the molten mixture, to grow the GaN crystals.

FIG. 10is a cross sectional view showing an eighth embodiment of the group III nitride crystal growing apparatus. InFIG. 10, those parts which are the same as those corresponding parts inFIG. 2are designated by the same reference numerals, and a description thereof will be omitted. An eighth embodiment of the group III nitride crystal, which is obtained by growing the GaN crystal by the group III nitride crystal growing apparatus shown inFIG. 10, becomes the same as the colorless transparent plate-shaped GaN crystal30shown inFIG. 3.

In this embodiment, the crystal growing process may be carried out under similar conditions as those of the first embodiment described above, except that the Li is added to the solution as a material which controls the ratio of growth rates of the group III nitride crystal in two approximately perpendicular directions.

In other words, this embodiment of the method of growing the group III nitride crystal comprises growing a group III nitride crystal from a solution in which an alkaline metal, a group III metal and nitrogen are dissolved, and including, in the solution, a material which controls a ratio of a growth rate of the group III nitride crystal in a first direction approximately parallel to a c-axis thereof and a growth rate of the group III nitride crystal in a second direction approximately perpendicular to the c-axis direction thereof.

Materials such as Li make the growth rate of the group III nitride crystal in the second direction higher than that in the first direction. In this case, it is possible to grow the plate-shaped group III nitride crystal30which extends in a planar manner along the second direction which is approximately perpendicular to the c-axis direction thereof.

On the other hand, materials such as Ni, Mn, Fe and Co, which are transition metals, make the growth rate of the group III nitride crystal in the first direction higher than that in the second direction. In this case, it is possible to grow a columnar group III nitride crystal which is elongated along the first direction which is approximately parallel to the c-axis direction thereof.

Of course, the material which controls the ratio of the growth rates in the first and second direction may control the ratio so that the two growth rates are the same.

Accordingly, it is possible to control the form or shape of the group III nitride crystal that is grown.

Furthermore, when the Li is added to the solution, the present inventors confirmed that the group III nitride crystal which is grown has a large resistance on the order of approximately several MΩ, even when no special impurity is mixed into the solution.

The following shows a comparison of the properties of the group III nitride crystals which are grown using the solution without Li (additive) and the solution with Li (additive), where “XRC FWHM” indicates a halfwidth of an X-ray rocking curve with respect to the grown group III nitride crystal, and “EPD” indicates the defect density obtained by the etch pit density evaluation.

Case 1: Without Li (Additive)

Ninth Embodiment

According to a ninth embodiment, Na is used as an alkaline metal, and Ga is used as a group III metal raw material. Nitrogen gas is used as nitrogen raw material, and Ni is added, to grow GaN crystals as a group III nitride.

The Na, Ga and Ni may be prepared in advance as a molten mixture within a solution container, and the nitrogen may be supplied during the crystal growth by fusion from a vapor phase into the molten mixture, to grow the GaN crystals.

FIG. 11is a cross sectional view showing a ninth embodiment of the group III nitride crystal growing apparatus. InFIG. 11, those parts which are the same as those corresponding parts inFIG. 10are designated by the same reference numerals, and a description thereof will be omitted.FIG. 12is a side view showing a columnar GaN crystal, that is, a ninth embodiment of the group III nitride crystal, which is obtained by growing the GaN crystal by the group III nitride crystal growing apparatus shown inFIG. 11.

In this embodiment, the crystal growing process may be carried out under similar conditions as those of the eighth embodiment described above, except that the Ni is added to the solution, in place of Li, as a material which controls the ratio of growth rates of the group III nitride crystal in two approximately perpendicular directions.

After the crystal growing process is carried out for 300 hours, colorless transparent columnar GaN crystals131having a length of 5 mm along the c-axis direction were grown on the inner walls of the solution container12.

On the other hand, when the Ni is not included in the solution25when carrying out a similar crystal growing process, it was found that a columnar GaN crystal having a short length along the c-axis and a large number of plate-shaped GaN crystals having the c-plane as the principal plane are grown.

The present inventors confirmed through experiments that the growth rate of the GaN crystal in the c-axis direction becomes higher when the Ni is mixed into the solution25, and that a larger columnar GaN crystal can be grown within a shorter time compared to the case where the Ni is not mixed into the solution25.

Accordingly, it is possible to control the columnar shape of the group III nitride crystal that is grown. In other words, since the group III nitride crystal can be grown in an ingot shape, a large number of group III nitride substrates can be produced at a low cost by slicing the ingot-shaped group III nitride crystal.

Tenth Embodiment

According to a tenth embodiment, Na is used as an alkaline metal, and Ga is used as a group III metal raw material. Nitrogen gas is used as nitrogen raw material, and Li is added using Li3N as a raw material, to grow GaN crystals as a group III nitride.

The Na, Ga and Li3N may be prepared in advance as a molten mixture within a solution container, and the nitrogen may be supplied during the crystal growth by fusion from a vapor phase into the molten mixture, to grow the GaN crystals.

FIG. 13is a cross sectional view showing a tenth embodiment of the group III nitride crystal growing apparatus. InFIG. 13, those parts which are the same as those corresponding parts inFIG. 10are designated by the same reference numerals, and a description thereof will be omitted.FIG. 14is a cross sectional view showing a plate-shaped GaN crystal, that is, a tenth embodiment of the group III nitride crystal, which is obtained by growing the GaN crystal by the group III nitride crystal growing apparatus shown inFIG. 13. In addition,FIG. 15is a cross sectional view showing a plate-shaped GaN crystal which is obtained by growing the GaN crystal by the group III nitride crystal growing apparatus shown inFIG. 13when no Li is added to the solution, for comparison purposes.

In this embodiment, the crystal growing process may be carried out under similar conditions as those of the eighth embodiment described above, except that the Li is added to the solution as a material which controls the ratio of growth rates of the group III nitride crystal in two approximately perpendicular directions, and that a plate-shaped GaN crystal having the c-plane as the principal plane is used as a seed crystal.

More particularly, the reaction chamber11is first separated from the group III nitride crystal growing apparatus at the valve21, and placed into a glove box (not shown) having an Ar atmosphere.

Then, a plate-shaped GaN crystal having the c-plane as the principal plane, is set in the solution container12, as a seed crystal132. Next, Ga is supplied as the group III metal raw material and Na is supplied as the alkaline metal, into the solution container12which is made of BN. A proportion of Na in the solution25is set to Na/(Na+Ga)=0.4.

In addition, Li3N is supplied as the Li raw material, into the solution container12.

Next, the solution container12is placed on the holder26and set within the reaction chamber11. Thereafter, the crystal growing process is carried out similarly to the eighth (or first) embodiment.

After the crystal growing process is carried out for 300 hours, a colorless transparent plate-shaped GaN crystal133having a smooth surface was grown on the seed crystal132, as shown inFIG. 14.

On the other hand, when the Li is not included in the solution25when carrying out a similar crystal growing process, it was found that a GaN crystal134having a rough surface was grown on the seed crystal132, as shown inFIG. 15.

Hence, it was confirmed that the plate-shaped GaN crystal133having the flat surface is obtained when the Li is mixed into the solution25. Furthermore, a halfwidth of an X-ray rocking curve with respect to the plate-shaped GaN crystal133was approximately 45 arcsec to approximately 55 arcsec and narrow, and the defect density was approximately 106cm−2or less by the etch pit density evaluation. Moreover, the plate-shaped GaN crystal133had a high resistance and was semiinsulative.

The present inventors confirmed through experiments that the growth rate of the GaN crystal in the direction perpendicular to the c-axis direction becomes higher when the Li is mixed into the solution25.

Accordingly, it is possible to control the plate shape of the group III nitride crystal that is grown. In other words, since the group III nitride crystal can be grown in a plate shape, the plate-shaped group III nitride crystal itself can be used as a group III nitride substrate, thereby reducing the production cost of the group III nitride substrate.

Eleventh Embodiment

FIG. 16Ais a cross sectional view showing an eleventh embodiment of the group III nitride crystal growing apparatus according to the present invention, andFIG. 16Bis a diagram showing a temperature distribution within a reaction chamber of the group III nitride crystal growing apparatus shown inFIG. 16Aalong a vertical direction. InFIG. 16B, the ordinate indicates the distance along the vertical direction of the reaction chamber in arbitrary units, and the abscissa indicates the temperature in arbitrary units.

The group III nitride crystal growing apparatus shown inFIG. 16Aincludes a reaction chamber211which is made of stainless steel and has a closed shape, and a solution container212which is accommodated within the reaction chamber211. The solution container212contains a solution216which includes an alkaline metal and is used to grow the group III nitride crystal. The solution container212may be removed from the reaction chamber211. In this embodiment, the solution container212is made of BN.

An upper heater213and a lower heater214are provided on the outer side of the reaction chamber211. Each of the upper and lower heaters213and214can be controlled to an arbitrary temperature.

The reaction chamber211can be removed from the group III nitride crystal growing apparatus. Hence, the reaction chamber211may be placed within a glove box without releasing the inside of the reaction chamber211to the atmosphere, and it is possible to work on the reaction chamber211within the glove box, such as preparing and setting a raw material within a high purity Ar gas atmosphere within the glove box. For this reason, it is possible to prevent moisture and impurities in the atmosphere from entering the reaction chamber211, so that a high-quality group III nitride crystal can be grown.

Next, a description will be given of an eleventh embodiment of the method of growing the group III nitride crystal according to the present invention, which grows GaN, by the group III nitride crystal growing apparatus shown inFIG. 16A.

First, the reaction chamber211is removed from the group III nitride crystal growing apparatus, and placed within a glove box (not shown) having an Ar atmosphere. Then, a GaN raw material217is supplied to the solution container212as a group III nitride raw material, and a solution216including Na as an alkaline metal is supplied to the solution container212. The solution container212is set within the reaction chamber211, and the reaction chamber211is sealed, so as to shut off the inside of the reaction chamber211from external atmosphere. The series of operations are carried out within the glove box having the high purity Ar gas atmosphere, and thus, the inside of the reaction chamber211is filled with the Ar gas.

Next, the reaction chamber211is removed from the glove box and assembled into the group III nitride crystal growing apparatus. In other words, the reaction chamber211is set at a predetermined position where the upper and lower heaters213and214are provided. The upper and lower heaters213and214are turned ON to raise the temperature of the reaction chamber211to a predetermined crystal growing temperature. More particularly, the lower heater214is set to a dissolving temperature of the GaN raw material217, and the upper heater213is set to a crystal growing temperature at which the GaN recrystallizes and is lower than a portion where the GaN raw material217exists. In this embodiment, the temperature of the portion where the GaN raw material217exists is set to 850° C., and the crystal growing temperature of the portion where the crystal growth takes place is set to 775° C.

The above described state is maintained for 500 hours, before decreasing the temperature of the reaction chamber211to the room temperature. When the reaction chamber211was opened after reducing the gas pressure within the reaction chamber211, it was found that several colorless transparent GaN single crystals218having a length of approximately 3 mm were grown in a recrystallization temperature region within the solution container212.

Twelfth Embodiment

FIG. 17Ais a cross sectional view showing a twelfth embodiment of the group III nitride crystal growing apparatus according to the present invention, andFIG. 17Bis a diagram showing a temperature distribution within a reaction chamber of the group III nitride crystal growing apparatus shown inFIG. 17Aalong a vertical direction. InFIG. 17B, the ordinate indicates the distance along the vertical direction of the reaction chamber in arbitrary units, and the abscissa indicates the temperature in arbitrary units.

The group III nitride crystal growing apparatus shown inFIG. 17Aincludes a reaction chamber221which is made of stainless steel and has a closed shape, and a solution container222which is accommodated within the reaction chamber221. The solution container222contains a solution226which includes an alkaline metal and is used to grow the group III nitride crystal. The solution container222may be removed from the reaction chamber221. In this embodiment, the solution container222is made of BN.

An upper heater223and a lower heater224are provided on the outer side of the reaction chamber221. Each of the upper and lower heaters223and224can be controlled to an arbitrary temperature.

The reaction chamber221can be removed from the group III nitride crystal growing apparatus. Hence, the reaction chamber221may be placed within a glove box without releasing the inside of the reaction chamber221to the atmosphere, and it is possible to work on the reaction chamber221within the glove box, such as preparing and setting a raw material within a high purity Ar gas atmosphere within the glove box. For this reason, it is possible to prevent moisture and impurities in the atmosphere from entering the reaction chamber221, so that a high-quality group III nitride crystal can be grown.

Next, a description will be given of a twelfth embodiment of the method of growing the group III nitride crystal according to the present invention, which grows GaN, by the group III nitride crystal growing apparatus shown inFIG. 17A.

First, the reaction chamber221is removed from the group III nitride crystal growing apparatus at a valve230, and placed within a glove box (not shown) having an Ar atmosphere. Then, a GaN raw material227is supplied to the solution container222as a group III nitride raw material, and a solution226including Na as an alkaline metal is supplied to the solution container222. The solution container222is set within the reaction chamber221, and the reaction chamber221is sealed, so as to shut off the inside of the reaction chamber221from external atmosphere. The series of operations are carried out within the glove box having the high purity Ar gas atmosphere, and thus, the inside of the reaction chamber221is filled with the Ar gas.

Next, the reaction chamber221is removed from the glove box and assembled into the group III nitride crystal growing apparatus. In other words, the reaction chamber221is set at a predetermined position where the upper and lower heaters223and224are provided, and connected at the valve230to a N2gas supply pipe229. The upper and lower heaters223and224are turned ON to raise the temperature of the reaction chamber221to a predetermined crystal growing temperature. More particularly, the lower heater224is set to a dissolving temperature of the GaN raw material227, and the upper heater223is set to a crystal growing temperature at which the GaN recrystallizes and is lower than a portion where the GaN raw material227exists. In this embodiment, the temperature of the portion where the GaN raw material227exists is set to 850° C., and the crystal growing temperature of the portion where the crystal growth takes place is set to 775° C.

The valve230and a valve232are opened to supply the N2gas from the N2gas supply pipe229to the reaction chamber221. The pressure of the N2gas is monitored by a pressure gage231, and controlled by a pressure control unit232. Hence, the pressure of the N2gas is adjusted by the pressure control unit232so that the total pressure within the reaction chamber221becomes 4 MPa.

The above described state is maintained for 500 hours, before decreasing the temperature of the reaction chamber221to the room temperature. When the reaction chamber221was opened after reducing the gas pressure within the reaction chamber221, it was found that several colorless transparent GaN single crystals228having a length of approximately 5 mm were grown in a recrystallization temperature region within the solution container222.

Thirteenth Embodiment

FIG. 18Ais a cross sectional view showing a thirteenth embodiment of the group III nitride crystal growing apparatus according to the present invention, andFIG. 18Bis a diagram showing a temperature distribution within a reaction chamber of the group III nitride crystal growing apparatus shown inFIG. 18Aalong a vertical direction. InFIG. 18B, the ordinate indicates the distance along the vertical direction of the reaction chamber in arbitrary units, and the abscissa indicates the temperature in arbitrary units.

The group III nitride crystal growing apparatus shown inFIG. 18Aincludes a reaction chamber241which is made of stainless steel and has a closed shape, and a solution container242which is accommodated within the reaction chamber241. The solution container242contains a solution246which includes an alkaline metal and is used to grow the group III nitride crystal. The solution container242may be removed from the reaction chamber241. In this embodiment, the solution container242is made of BN.

A gas supply pipe249is connected to the reaction chamber241, so that an internal space245within the reaction chamber241may be filled with N2gas and Ar gas for suppressing evaporation of an alkaline metal. The N2gas pressure and the Ar gas pressure within the reaction chamber241are controllable.

The gas supply pipe249branches to a N2gas supply pipe254via a valve252, and branches to an Ar gas supply pipe257via a valve255. The pressure within the N2gas supply pipe254is controllable by a pressure control unit253, and the pressure within the Ar gas supply pipe257is controllable by a pressure control unit256.

The total pressure within the reaction chamber is monitored by a pressure gage251which is provided on the gas supply pipe249. The Ar gas is mixed as an inert gas in order to suppress evaporation of the alkaline metal and to independently control the pressure of the N2gas. Hence, a crystal growth with a high controllability is achieved.

An upper heater243and a lower heater244are provided on the outer side of the reaction chamber241. Each of the upper and lower heaters243and244can be controlled to an arbitrary temperature.

The reaction chamber241can be removed from the group III nitride crystal growing apparatus. Hence, the reaction chamber241may be placed within a glove box without releasing the inside of the reaction chamber241to the atmosphere, and it is possible to work on the reaction chamber241within the glove box, such as preparing and setting a raw material within a high purity Ar gas atmosphere within the glove box. For this reason, it is possible to prevent moisture and impurities in the atmosphere from entering the reaction chamber241, so that a high-quality group III nitride crystal can be grown.

Next, a description will be given of a thirteenth embodiment of the method of growing the group III nitride crystal according to the present invention, which grows GaN, by the group III nitride crystal growing apparatus shown inFIG. 18A.

First, the reaction chamber241is removed from the group III nitride crystal growing apparatus at a valve250, and placed within a glove box (not shown) having an Ar atmosphere. Then, a GaN raw material247is supplied to the solution container242as a group III nitride raw material, and a solution246including Na as the alkaline metal is supplied to the solution container242. In this embodiment, plate-shaped crystals having an approximately stoichiometry composition, grown within a molten mixture of Na and Ga under a N2pressure of 5 MPa, were used as the GaN raw material247.

Thereafter, the Na within the solution container242is fused, and a GaN seed crystal248is hanged from an upper portion of the solution container242and held at a predetermined position within a Na solution246. The solution container242is set within the reaction chamber241, and the reaction chamber241is sealed, so as to shut off the inside of the reaction chamber241from external atmosphere. The series of operations are carried out within the glove box having the high purity Ar gas atmosphere, and thus, the inside of the reaction chamber241is filled with the Ar gas.

Next, the reaction chamber241is removed from the glove box and assembled into the group III nitride crystal growing apparatus. In other words, the reaction chamber241is set at a predetermined position where the upper and lower heaters243and244are provided, and connected at the valve250to the gas supply pipe249. The upper and lower heaters243and244are turned ON to raise the temperature of the reaction chamber241to a predetermined crystal growing temperature. More particularly, the lower heater244is set to a dissolving temperature of the GaN raw material247, and the upper heater243is set to a crystal growing temperature at which the GaN seed crystal248grows and is lower than a portion where the GaN raw material247exists. In this embodiment, the temperature of the portion where the GaN raw material247exists is set to 850° C., and the crystal growing temperature of the portion where the crystal growth of the GaN seed crystal248takes place is set to 775° C.

The valve250and the valve255are opened to supply the Ar gas from the Ar gas supply pipe257, and the pressure is controlled by the pressure control unit256to control the total pressure within the reaction chamber241to 4 MPa, before closing the valve255. Then, the valve252is opened to supply the N2gas from the N2gas supply pipe254, and the pressure is controlled by the pressure control unit253to control the total pressure within the reaction chamber241to 8 MPa. In other words, the Ar partial pressure and the N2partial pressure in the internal space245within the reaction chamber241are respectively set to 4 MPa.

The above described state is maintained for 500 hours, before decreasing the temperature of the reaction chamber241to the room temperature. When the reaction chamber241was opened after reducing the gas pressure within the reaction chamber241, it was found that a colorless transparent GaN single crystal258having a length of approximately 10 mm was grown on the GaN seed crystal248within the solution container242.

Therefore, according to the eleventh through thirteenth embodiments, the method of growing a group III nitride crystal, comprises dissolving a group III nitride into a solution including an alkaline metal, and recrystallizing a group III nitride crystal at a location different from a location where the group III nitride is dissolved within the solution. In other words, when the group III nitride is held at a predetermined temperature within the solution which includes the alkaline metal, the group III nitride dissolves into the solution with a certain solubility. The dissolved group III nitride recrystallizes at a location where the supersaturation becomes large, such as a location where the temperature is low and a location where the nitrogen concentration is high. Hence, the group III nitride raw material is dissolved to recrystallize and grow the group III nitride crystal.

The group III nitride may be selected from group III metals such as Ga, Al and In. In addition, the group III nitride may be selected from compounds of nitrogen and one or a plurality of such group III metals. On the other hand, the alkaline metal may be selected from Na, K or other suitable alkaline metals. It is possible to dissolve another material within the solution which includes the alkaline metal. For example, the solution which includes the alkaline metal may be doped by fusing an n-type impurity or a p-type impurity.

According to the eleventh through thirteenth embodiments, the raw material required for the crystal growth is stably supplied without the possibility of clogging the supply pipe, and a practically large group III nitride crystal having a high quality can be grown.

It is desirable that the solution contacts the N2gas. In other words, the solution into which the group III nitride is dissolved, desirably contacts the N2gas having a predetermined partial pressure at a gas-liquid interface. When the group III nitride dissolves into the solution, the nitrogen generated by the decomposition of the group III nitride assumes a gaseous state and the nitrogen concentration within the solution decreases. Accordingly, the amount of nitrogen raw material becomes insufficient compared to the group III raw material. For this reason, the predetermined N2partial pressure is applied on the solution and the N2partial pressure is adjusted, so as to present lack of the nitrogen raw material. In addition, by controlling the nitrogen concentration within the solution, it is possible to control the crystal growth rate and the crystal quality when growing the group III nitride crystal.

Therefore, when the solution which includes the alkaline metal contacts the N2gas, it is possible to suppress escaping of the nitrogen from the solution, to thereby prevent the lack of the nitrogen raw material and grow a high-quality group III nitride crystal. In addition, it is possible to control the nitrogen concentration within the solution by controlling the N2partial pressure in the vapor phase, and the group III nitride crystal can be grown by controlling the crystal growth rate and the crystal quality. Consequently, it is possible to grow a practically large group III nitride crystal having a high quality.

The group III nitride which is dissolved into the solution may comprise plate-shaped crystals. Since the plate-shaped crystals more easily dissolve into the solution which includes the alkaline metal as compared to columnar crystals, the dissolving rate of the group III nitride is high, thereby enabling a stable supply of the raw material required for the recrystallization. As a result, it is possible to grow a practically large group III nitride crystal having a high quality.

The group III nitride which is dissolved into the solution may comprise an approximately stoichiometry composition. If the group III nitride raw material greatly deviates from the stoichiometry composition, the crystal growth rate may decrease and the grown crystal may deviate from the stoichiometry composition to deteriorate the crystal quality. Accordingly, by dissolving the group III nitride having an approximately stoichiometry composition into the solution which includes the alkaline metal, it is possible recrystallize and grow the group III nitride crystal having an approximately stoichiometry composition.

The group III nitride which is dissolved into the solution may comprise group III nitride crystals which are grown from a material which comprises nitrogen and a mixture of an alkaline metal and a group III metal. In this case, the nitrogen defect can be reduced, and it is possible to grow a high purity group III nitride crystal having an approximately stoichiometry composition. As a result, it is possible to grow a practically large group III nitride crystal having a high quality.

The group III nitride crystal may be grown on a seed crystal. In this case, it is possible to grow a practically large group III nitride crystal having a high quality.

Fourteenth Embodiment

A fourteenth embodiment of the method of growing the group III nitride crystal forms, within a reaction chamber, a molten mixture of an alkaline metal and a material which includes a group III metal, grows a group III nitride crystal which is made of the group III metal and nitrogen, from the molten mixture and a material which includes the nitrogen, and controls a temperature in a vicinity of a surface of the molten mixture and a temperature of a crystal growing region within the molten mixture, so that the nitrogen dissolves into the molten mixture from the surface and the group III nitride crystal grows in the crystal growing region which is other than the surface.

The group III metal may be selected from Ga, Al, In and the like. In addition, the alkaline metal may be selected from K, Na and the like. In addition, the material which includes nitrogen may be any suitable compound including nitrogen, such as nitrogen (N2) gas, sodium azide (NaN3), and ammonia (NH3).

As long as the temperature in the vicinity of the surface of the molten mixture and the temperature of the crystal growing region are controlled, the two temperatures may be the same or mutually different temperatures.

Therefore, it is possible to grow a large group III nitride crystal under a crystal growing temperature condition that generates no nucleus of the group III nitride crystal in the vicinity of the surface of the molten mixture, that is, by growing the group III nitride crystal in the crystal growing region which is other than the surface of the molten mixture.

FIG. 19is a cross sectional view showing a fourteenth embodiment of the group III nitride crystal growing apparatus according to the present invention. The group III nitride crystal growing apparatus shown inFIG. 19includes a reaction chamber1101, and a solution container1102which is provided within the reaction chamber1101. The solution container1102contains a molten mixture1103which includes Ga and Na. In this embodiment, the Ga is used as the material which includes the group III metal, and the Na is used as the alkaline metal. The alkaline metal, namely, the Na, may be supplied from outside the reaction chamber1101or, initially provided within the solution container1102.

A lid1109is provided on top of the solution container1102, and a gap is provided between the solution container1102and the lid109for allowing gas input and output with respect to the solution container1102. The reaction chamber1101is made of stainless steel, for example. On the other hand, the solution container1102is made of BN, AlN or pyrolitic BN.

A first heater1106and a second heater1107are provided on the outer side of the solution container1102, so that the group III nitride (GaN) may be controlled to the crystal growing temperature. The first heater1106is disposed under the second heater1107, so that the second heater1107mainly heats the upper portion of the solution container1102and the first heater1106mainly heats the lower portion of the solution container1102.

A first temperature sensor1112for detecting the temperature at the lower portion of the solution container1102is provided at the lower portion of the solution container1102. A second temperature sensor1113for detecting the temperature at the upper portion of the solution container1102is provided at the upper portion of the solution container1102. An output of the first temperature sensor1112is coupled to the first heater1106to enable a feedback control of the first heater1106, so that the lower portion of the solution container1102is controlled to a desired temperature. Similarly, an output of the second temperature sensor1113is coupled to the second heater1107to enable a feedback control of the second heater1107, so that the upper portion of the solution container1102is controlled to a desired temperature.

The material which includes nitrogen may be N2gas. InFIG. 19, a N2gas container1114which contains the N2gas is provided outside the reaction chamber1101. The N2gas from the N2gas container1114can be supplied to a space1108within the reaction chamber1101via a gas supply pipe1104. In this embodiment, the N2gas is supplied from a lower portion of the reaction chamber1101. In order to adjust the pressure of the N2gas, a pressure gage1111is provided to detect the pressure of the N2gas within the reaction chamber1101, and a pressure adjusting valve1105is provided to adjust the pressure of the N2gas via the gas supply pipe1104. An output of the pressure gage1111is coupled to the pressure adjusting valve1105to enable a feedback control of the pressure adjusting valve1105, so that the pressure within the reaction chamber1101is controlled to a desired pressure.

In this embodiment, the N2pressure within the reaction chamber1101is set to 3 MPa, the temperature at the upper portion of the solution container1102is set to 1000° C., the temperature at the lower portion of the solution container1102is set to 850° C., and a seed crystal is initially set in the lower portion of the solution container1102. In this state, the above described pressure and temperatures are maintained, so that a GaN crystal1110grows on the nucleus of the seed crystal.

The GaN crystal1110does not grow at the surface of the molten mixture1103, and the GaN crystal1110grows only in the crystal growing region at the lower portion of the solution container1102where the seed crystal is set. The nitrogen dissolves into the molten mixture1103from the surface of the molten mixture1103, and the GaN crystal1110grows only in the crystal growing region where the seed crystal is set.

Because the crystal growth does not occur at the surface of the molten mixture1103and the crystal growth occurs only in the intended crystal growing region, the raw material is efficiently utilized, and a high-quality GaN crystal can be grown by controlling the generation of the nucleus of the GaN.

FIG. 20is a perspective view showing a columnar GaN crystal which is obtained by growing the GaN crystal by the group III nitride crystal growing apparatus shown inFIG. 19.

When a GaN crystal1301shown inFIG. 20is set as the seed crystal at the lower portion of the solution container1102, the GaN crystal grows on the GaN seed crystal1301by maintaining the crystal growth conditions described above, and a columnar GaN crystal1302is obtained.

The GaN seed crystal1301has a hexagonal column shape, and thus, a hexagonal columnar GaN crystal1302is grown on the GaN seed crystal1301. InFIG. 20, top and bottom surfaces of the hexagonal column shape are the c-plane.

FIG. 21is a diagram showing a relationship between a crystal growing temperature and a crystal growing pressure for the group III nitride crystal. InFIG. 21, the ordinate indicates the N2pressure (P) within the reaction chamber1101in MPa, and the abscissa indicates the inverse of the absolute temperature (1/T) of the molten mixture1103in “×10−3K−1”. Different crystal forms are obtain in four regions A, B, C and D shown inFIG. 21.

In the region A, no group III nitride crystal grows and the group III nitride crystal decomposes. In the region B, the group III nitride crystal grows only on the seed crystal, and no group III nitride crystal grows on the inner walls or the like of the solution container1102(or reaction chamber1101). In the regions C and D, the nucleus of the group III nitride is naturally generated, and the group III nitride crystal also grows on the inner walls and the like of the solution container1102(or reaction chamber1101). The columnar crystal grows dominantly in the region C, while the plate-shaped crystal grows dominantly in the region D.

In this embodiment, the temperature and pressure at the surface of the molten mixture1103correspond to those in the region A shown inFIG. 21. On the other hand, the temperature and pressure at the lower portion of the solution container1102where the seed crystal is set correspond to those in the region B shown inFIG. 21.

Because the crystal growth occurs dominantly on the seed crystal in the region B shown inFIG. 21, the crystal growth is unlikely to newly occur in regions other than that of the seed crystal, thereby enabling efficient utilization of the raw material. In other words, virtually all of the raw material is used by the GaN crystal which grows on the seed crystal, and the Ga which is initially prepared and set in the solution container1102is efficiently utilized. As a result, it is possible to grow a large GaN crystal without having to use a large amount of Ga.

In addition, the crystal orientation of the group III nitride crystal can easily be controlled, because the group III nitride crystal can be grown on the seed crystal. In other words, by using as the seed crystal a GaN crystal or the like having a predetermined crystal orientation, it is possible to accurately control the crystal orientation of the group III nitride crystal which is grown. As a result, when finally slicing the group III nitride crystal which is obtained, it is possible to easily obtain the desired crystal orientation. Hence, a GaN substrate or the like can be obtained with the desired crystal orientation by slicing the GaN crystal which is obtained.

Therefore, according to this embodiment, it is possible to obtain a group III nitride crystal having a high quality and low defect density.

InFIG. 20, the GaN seed crystal1301used has the hexagonal column shape. However, the seed crystal may have other shapes, such as a plate-shape, as will be described later in conjunction with a sixteenth embodiment. Furthermore, the group III nitride crystal may be grown on an epitaxial layer. In this case, it is possible to obtain a large plate-shaped group III nitride crystal such as the GaN crystal.

Fifteenth Embodiment

A fifteenth embodiment of the method of growing the group III nitride crystal is based on the fourteenth embodiment described above, and fills a space within the reaction chamber by the material which includes the nitrogen and in a gaseous state, and controls a pressure within the reaction chamber so that a partial pressure of the material which includes the nitrogen and is in the gaseous state generates no nucleus of the group III nitride in the vicinity of the surface in response to a temperature change at the surface. The space within the reaction chamber may include a gas other than the material which includes the nitrogen.

The temperature and pressure at the surface of the molten mixture are set to those of the region A or B shown inFIG. 21, and temperature and pressure in the region other than the surface of the molten mixture are set to those of the region B or C or D shown inFIG. 21so that the crystal growth occurs in the region.

The group III nitride crystal does not grow at the surface of the molten mixture, and the nitrogen dissolves into the molten mixture from the surface of the molten mixture. The nitrogen which dissolves into the molten mixture diffuses to the region other than the surface of the molten mixture, and the group III nitride crystal grows under the pressure and temperature conditions of the region B or C or D shown inFIG. 21.

Therefore, the pressure and the atmosphere can be controlled with ease according to this embodiment. Moreover, by setting the partial pressure of the material (gas) which includes the nitrogen to a constant value and generating a temperature change, it becomes easy to dissolve the nitrogen into the molten mixture from the surface of the molten mixture and to grow the group III nitride crystal in the region other than the surface of the molten mixture.

A fifteenth embodiment of the group III nitride crystal growing apparatus may have the same structure as that shown inFIG. 19, but operated under different conditions. In this embodiment, the N2pressure within the reaction chamber1101is set to 3 MPa, the temperature at the upper portion of the solution container1102is set to 1000° C., and the temperature at the lower portion of the solution container1102is set to 800° C. In this state, the above described pressure and temperatures are maintained, so that a GaN crystal1110grows at the lower portion of the solution container1102.

In this case, the GaN crystal1110does not grow at the surface of the molten mixture1103, and the GaN crystal1110grows only at the lower portion of the solution container1102. The nitrogen dissolves into the molten mixture1103from the surface of the molten mixture1103, and the GaN crystal grows only at the lower portion of the solution container1102. In this state, a columnar GaN crystal1401A shown inFIG. 22or a columnar GaN crystal1401B shown inFIG. 23grows dominantly at the lower portion of the solution container1102.FIG. 22is a perspective view showing the columnar GaN crystal1401A which may be obtained by growing the GaN crystal by this fifteenth embodiment, andFIG. 23is a perspective view showing the columnar GaN crystal1401B which may be obtained by this embodiment.

The columnar GaN crystal1401A shown inFIG. 22has a hexagonal column shape, while the columnar GaN crystal1401B shown inFIG. 23has shape which is a combination of a hexagonal column shape with a hexagonal pyramid shape on top. InFIGS. 22 and 23, bottom surfaces of the hexagonal column shapes of the columnar GaN crystals1401A and1401B are the c-plane. In other words, the columnar GaN crystals1401A and1401B shown inFIGS. 22 and 23extend in the c-axis direction.

Since this embodiment does not grow the GaN crystal at the surface of the molten mixture1103and grows the GaN crystal only in the predetermined intended region, the raw material is efficiently utilized, and a high-quality GaN crystal can be grown by controlling the nucleus generation.

In this embodiment, the temperature and pressure at the surface of the molten mixture1103correspond to those of the region A shown inFIG. 21, and the temperature and pressure at the lower portion of the molten mixture1103where the GaN crystal grows correspond to those of the region C shown inFIG. 21.

Because the columnar GaN crystal grows dominantly in the region C shown inFIG. 21, the crystal orientation is definite. Hence, when making a GaN substrate from the columnar GaN crystal, it is easy to determine the crystal orientation and the slicing of the columnar GaN crystal.

In addition, since the columnar GaN crystal grows from the natural nucleus generation in the region C shown inFIG. 21, even when there is no seed crystal, it is possible to use the columnar GaN crystal which is grown in the region C as the seed crystal which is used in the region B.

Sixteenth Embodiment

A sixteenth embodiment of the method of growing the group III nitride crystal is based on the fourteenth embodiment described above, and the temperature in the vicinity of the surface of the molten mixture is controlled to a temperature which is higher than the temperature of the crystal growing region. In other words, the group III nitride crystal is grown in the region having a lower temperature than the surface of the molten mixture, and the group III nitride crystal is not grown at the surface of the molten mixture. The temperature is higher towards the left side along the abscissa inFIG. 21.

According to this embodiment, it is possible to set a large margin for the crystal growing conditions. That is, since the region A shown inFIG. 21becomes the higher temperature region and it is easy to set the regions B, C and D as the lower temperature regions having a lower temperature than the region A, it is possible to set a large margin for the crystal growing conditions. As a result, it is possible to grow group III nitride crystals having various forms, as will be described later.

A sixteenth embodiment of the group III nitride crystal growing apparatus may have the same structure as that shown inFIG. 19, but operated under different conditions. In this embodiment, the N2pressure within the reaction chamber1101is set to 3 MPa, the temperature at the upper portion of the solution container1102is set to 1000° C., and the temperature at the lower portion of the solution container1102is set to 730° C. In this state, the above described pressure and temperatures are maintained, so that a GaN crystal1110grows at the lower portion of the solution container1102.

In this case, the GaN crystal1110does not grow at the surface of the molten mixture1103, and the GaN crystal1110grows only at the lower portion of the solution container1102. The nitrogen dissolves into the molten mixture1103from the surface of the molten mixture1103, and the GaN crystal grows only at the lower portion of the solution container1102. In this state, a plate-shaped GaN crystal1501shown inFIG. 24grows dominantly at the lower portion of the solution container1102.FIG. 24is a perspective view showing the plate-shaped GaN crystal1501which is obtained by growing the GaN crystal by this sixteenth embodiment.

The group III nitride crystal which is grown by this sixteenth embodiment is not limited to the hexagonal plate-shaped GaN crystal1501shown inFIG. 24, and group III nitride crystals having shapes other than the hexagonal plate shape may be grown. For example, a polygonal plate-shaped group III nitride crystal of the hexagonal system may be grown by this embodiment. In each case, the plate-shaped group III nitride crystal extends parallel to the (0001) face, that is, the c-plane.

Since this embodiment does not grow the GaN crystal at the surface of the molten mixture1103and grows the GaN crystal only in the predetermined intended region, the raw material is efficiently utilized, and a high-quality GaN crystal can be grown by controlling the nucleus generation.

In this embodiment, the temperature and pressure at the surface of the molten mixture1103correspond to those of the region A shown inFIG. 21, and the temperature and pressure at the lower portion of the molten mixture1103where the GaN crystal grows correspond to those of the region D shown inFIG. 21.

Because the plate-shaped GaN crystal grows dominantly in the region D shown inFIG. 21, the plate-shaped GaN crystal may be used as it is as a GaN substrate. Furthermore, even when undulations are formed on the surface of the plate-shaped GaN crystal, the surface undulations can be eliminated by simply polishing the crystal surface so that the plate-shaped GaN crystal may be used as the GaN substrate.

The crystal growth rate in the in-plane direction of the plate-shaped group III nitride crystal is high in the region D shown inFIG. 21. For this reason, the GaN crystal can be grown efficiently at a low cost.

In addition, since the plate-shaped GaN crystal grows from the natural nucleus generation in the region D shown inFIG. 21, even when there is no seed crystal, it is possible to use the plate-shaped GaN crystal which is grown in the region D as the seed crystal which is used in the region B.

Seventeenth Embodiment

A seventeenth embodiment of the method of growing the group III nitride crystal is based on the sixteenth embodiment described above, and sets a seed crystal in the crystal growing region, and controls the temperature and a pressure in the crystal growing region, so that the group III nitride crystal grows on the seed crystal.

More particularly, the temperature and pressure of the region where the seed crystal is set are controlled to be those of the region B shown inFIG. 21. On the other hand, the temperature and pressure at the surface of the molten mixture are controlled to be those of the region A shown inFIG. 21. Under these crystal growing conditions, the nitrogen dissolves into the molten mixture from the surface of the molten mixture, and the group III nitride crystal grows only on the seed crystal which is set in the region described above.

The seed crystal may be made of any group III nitride, as long as it functions as a seed crystal. Hence, the seed crystal may be made of the same material as the group III nitride crystal which grows in the molten mixture or, may be made of a material different from that of the group III nitride crystal which grows in the molten mixture. Although the group III nitride crystal grows on the seed crystal even when the seed crystal is made of the material which is different from that of the group III nitride crystal which grows in the molten mixture, it is desirable from the point of view of obtaining a high quality crystal that the seed crystal is made of the same material as the group III nitride crystal which grows in the molten mixture.

Since the group III nitride crystal does not grow at the surface of the molten mixture and grows only in the intended predetermined region of the molten mixture, the raw material is efficiently utilized, and a high-quality crystal can be grown by controlling the nucleus generation.

Because the crystal growth occurs dominantly on the seed crystal in the region B shown inFIG. 21, the crystal growth is unlikely to newly occur in regions other than that of the seed crystal, thereby enabling efficient utilization of the raw material. In other words, virtually all of the raw material is used by the group III nitride (GaN) crystal which grows on the seed crystal, and the group III metal (Ga) which is initially prepared and set in the solution container1102is efficiently utilized. As a result, it is possible to grow a large group III nitride (GaN) crystal without having to use a large amount of group III metal (Ga).

In addition, the crystal orientation of the group III nitride crystal can easily be controlled, because the group III nitride crystal can be grown on the seed crystal. In other words, by using as the seed crystal a GaN crystal or the like having a predetermined crystal orientation, it is possible to accurately control the crystal orientation of the group III nitride crystal which is grown. As a result, when finally slicing the group III nitride crystal which is obtained, it is possible to easily obtain the desired crystal orientation. Hence, a GaN substrate or the like can be obtained with the desired crystal orientation by slicing the GaN crystal which is obtained.

Therefore, according to this embodiment, it is possible to obtain a group III nitride crystal having a high quality and low defect density.

A seventeenth embodiment of the group III nitride crystal growing apparatus may have the same structure as that shown inFIG. 19, but operated under different conditions. In this embodiment, the N2pressure within the reaction chamber1101is set to 2 MPa, the temperature at the upper portion of the solution container1102is set to 850° C., and the temperature at the lower portion of the solution container1102is also set to 850° C. Further, a seed crystal is initially prepared and set in the lower portion of the solution container1102. In this state, the above described pressure and temperatures are maintained, so that a GaN crystal1110grows at the lower portion of the solution container1102using the seed crystal as the nucleus.

Although the seed crystal is set in the lower portion of the solution container1102, that is, the lower portion of the molten mixture1103, it is of course possible to obtain similar effects by setting the seed crystal on the side wall or the like of the solution container1102.

The effects obtainable in this embodiment are basically the same as those obtainable by the fourteenth embodiment described above, except that the temperatures of the upper and lower portions of the solution container1102are set to the same temperature in this embodiment. And since the temperatures at the upper and lower portions of the solution container1102are the same, the temperature of the entire molten mixture1103becomes uniform, and the thermal deviation becomes small, thereby making it possible to grow the group III nitride (GaN) crystal under stable crystal growing conditions.

Eighteenth Embodiment

An eighteenth embodiment of the method of growing the group III nitride crystal is based on the sixteenth embodiment described above, and controls the temperature and a pressure in the crystal growing region, so that a columnar group III nitride crystal grows in the crystal growing region.

More particularly, the temperature and pressure in the region within the molten mixture where the columnar group III nitride crystal grows are controlled to those of the region C shown inFIG. 21. On the other hand, the temperature and pressure at the surface of the molten mixture are controlled to those of the region A or B shown inFIG. 21. Hence, the group III nitride crystal does not grow at the surface of the molten mixture, and the nitrogen dissolves into the molten mixture from the surface of the molten mixture. In other words, the columnar group III nitride crystal grows because the temperature and pressure are controlled to those of the region C shown inFIG. 21only in the region within the molten mixture where the columnar group III nitride crystal grows.

Since this embodiment does not grow the GaN crystal at the surface of the molten mixture1103and grows the GaN crystal only in the predetermined intended region, the raw material is efficiently utilized, and a high-quality GaN crystal can be grown by controlling the nucleus generation.

Moreover, because the columnar GaN crystal grows dominantly in the region C shown inFIG. 21, the crystal orientation is definite. Hence, when making a GaN substrate from the columnar GaN crystal, it is easy to determine the crystal orientation and the slicing of the columnar GaN crystal.

An eighteenth embodiment of the group III nitride crystal growing apparatus may have the same structure as that shown inFIG. 19, but operated under different conditions. In this embodiment, the N2pressure within the reaction chamber1101is set to 2 MPa, the temperature at the upper portion of the solution container1102is set to 800° C., and the temperature at the lower portion of the solution container1102is set to 850° C. Further, a seed crystal is initially prepared and set in the lower portion of the solution container1102. In this state, the above described pressure and temperatures are maintained, so that a GaN crystal1110grows at the lower portion of the solution container1102using the seed crystal as the nucleus.

Although the seed crystal is set in the lower portion of the solution container1102, that is, the lower portion of the molten mixture1103, it is of course possible to obtain similar effects by setting the seed crystal on the side wall or the like of the solution container1102.

The effects obtainable in this embodiment are basically the same as those obtainable by the fourteenth or seventeenth embodiment described above, except that the temperature of the upper portion of the solution container1102is lower than the temperature of the lower portion of the solution container1102in this embodiment. And since the temperatures at the upper and lower portions of the solution container1102are different, convection of the molten mixture1103occurs, thereby scattering the nitrogen which dissolves into the molten mixture1103from the surface of the molten mixture1103, throughout the entire molten mixture1103, to realize a uniform nitrogen concentration. As a result, it is possible to realize a stable growth of the GaN crystal.

Although N2gas is used as the material which includes nitrogen, it is also possible to supply to the reaction chamber1101other materials which include the nitrogen, such as sodium azide (NaN3), and ammonia (NH3) gas.

It is also possible to supply to the reaction chamber1101a gas mixture of the material which includes the nitrogen and an inert gas such as Ar gas, where the material which includes the nitrogen may be nitrogen (N2) gas, sodium azide (NaN3) or ammonia (NH3) gas. The inert gas that is used does not react with the alkaline metal, the material which includes the group III metal or the material which includes the nitrogen.

Even in the case where the gas mixture of the material which includes the nitrogen (nitrogen (N2) gas, sodium azide (NaN3) or ammonia (NH3) gas) and the inert gas (Ar gas) is supplied to the reaction chamber1101, the pressure at which the group III nitride crystal is grown is determined by the effective N2gas pressure within the reaction chamber1101, and not the total pressure of the gas mixture.

Nineteenth Embodiment

A nineteenth embodiment of the method of growing the group III nitride crystal is based on the sixteenth embodiment described above, and controls the temperature and a pressure in the crystal growing region, so that a plate-shaped group III nitride crystal grows in the crystal growing region.

More particularly, the temperature and pressure in the region within the molten mixture where the plate-shaped group III nitride crystal grows are controlled to those of the region D shown inFIG. 21. On the other hand, the temperature and pressure at the surface of the molten mixture are controlled to those of the region A or B shown inFIG. 21. Hence, the group III nitride crystal does not grow at the surface of the molten mixture, and the nitrogen dissolves into the molten mixture from the surface of the molten mixture. In other words, the plate-shaped group III nitride crystal grows because the temperature and pressure are controlled to those of the region D shown inFIG. 21only in the region within the molten mixture where the plate-shaped group III nitride crystal grows.

Since this embodiment does not grow the GaN crystal at the surface of the molten mixture1103and grows the GaN crystal only in the predetermined intended region, the raw material is efficiently utilized, and a high-quality GaN crystal can be grown by controlling the nucleus generation.

Moreover, because the plate-shaped GaN crystal grows dominantly in the region D shown inFIG. 21, the plate-shaped GaN crystal may be used as it is as a GaN substrate. Furthermore, even when undulations are formed on the surface of the plate-shaped GaN crystal, the surface undulations can be eliminated by simply polishing the crystal surface so that the plate-shaped GaN crystal may be used as the GaN substrate.

The crystal growth rate in the in-plane direction of the plate-shaped group III nitride crystal is high in the region D shown inFIG. 21. For this reason, the GaN crystal can be grown efficiently at a low cost.

Twentieth Embodiment

A twentieth embodiment of the method of growing the group III nitride crystal is based on the sixteenth embodiment described above, and locates the crystal growing region in a lower portion of the reaction chamber.

The lower portion of the reaction chamber refers to a region which is lower than the surface of the molten mixture from which the nitrogen dissolves into the molten mixture.

According to this embodiment, a large group III nitride crystal can be grown continuously within the molten mixture. In other words, stable crystal growing conditions are obtained in the molten mixture, such as small temperature deviation and a constant ratio of raw materials, thereby making it possible to grow a large group III nitride crystal having a high quality.

A twenty-first embodiment of the method of growing the group III nitride crystal is based on the fourteenth embodiment described above, and controls the temperature in the vicinity of the surface of the molten mixture and the temperature of the crystal growing region to approximately same temperature.

More particularly, the temperature and pressure of the region within the molten mixture1103where the group III nitride crystal grows are set to those of the region B shown inFIG. 21, and the group III nitride crystal grows only on the seed crystal. Since the pressure of the material (gas) including nitrogen is approximately constant within the reaction chamber1101, the temperature in the vicinity of the surface of the molten mixture1103and the temperature of the crystal growing region within the molten mixture1103may be regarded as being approximately the same as long as the temperatures are controlled within the temperature range of the region B shown inFIG. 21.

Therefore, according to this embodiment, the temperature within the entire molten mixture becomes uniform and the thermal deviation becomes small, because the temperature in the vicinity of the surface of the molten mixture and the temperature of the crystal growing region are controlled to approximately the same temperature. Hence, the group III nitride crystal can be grown under stable crystal growing conditions. As a result, it is possible to grow a large group III nitride crystal having a high quality.

A twenty-second embodiment of the method of growing the group III nitride crystal is based on the fourteenth embodiment described above, and controls the temperature in the vicinity of the surface of the molten mixture to a temperature which is lower than a temperature at a lower portion of the molten mixture within the reaction chamber.

More particularly, the lower portion of the molten mixture1103refers to a portion lower than the vicinity of the surface of the molten mixture1103. The temperature and pressure of the region within the molten mixture1103where the group III nitride crystal grows are set to those of the region B shown inFIG. 21, and the group III nitride crystal grows only on the seed crystal.

Therefore, according to this embodiment, convection is generated in the molten mixture, because the temperature in the vicinity of the surface of the molten mixture is controlled to be lower than the temperature of the lower portion of the molten mixture. Hence, the convection of the molten mixture scatters the nitrogen which dissolves into the molten mixture from the surface of the molten mixture, to make the nitrogen concentration uniform within the entire molten mixture. As a result, the group III nitride crystal can be grown under stable crystal growing conditions, and it is possible to grow a large group III nitride crystal having a high quality.

According to the fourteenth through twenty-second embodiments, it is possible to improve the positional controllability and the growth parameter controllability, and to efficiently dissolve the nitrogen into the molten mixture and to efficiently utilize the group III metal, so as to grow a large group III nitride crystal.

Embodiments of Semiconductor Device

FIG. 25is a perspective view showing an important part of a first embodiment of a semiconductor device according to the present invention. This embodiment of the semiconductor device uses a GaN substrate which is obtained by any of the above described embodiments of the method of growing the group III nitride crystal or the group III nitride crystal growing apparatus. For the sake of convenience, it is assumed that the GaN substrate used is obtained by the group III nitride crystal growing apparatus shown inFIG. 19.

A semiconductor laser shown inFIG. 25has an n-type GaN substrate601which is obtained by the group III nitride crystal growing apparatus shown inFIG. 19. An n-type AlGaN clad layer602, an n-type GaN guide layer603, an InGaN Multi-Quantum-Well (MQW) active layer604, a p-type GaN guide layer605, a p-type AlGaN clad layer606and a p-type GaN contact layer607are successively stacked on the n-type GaN substrate601. The layers on the n-type GaN substrate601may be formed by thin film crystal growing techniques such as Metal Organic Vapor Phase Epitaxy (MO-VPE) and Molecular Beam Epitaxy (MBE).

A ridge structure is formed by the stacked layers of GaN, AlGaN and InGaN, and a SiO2insulator layer608has a hole at the p-type GaN contact layer607. A p-type (Au/Ni) ohmic electrode609and an n-type (Al/Ti) ohmic electrode610are respectively disposed on top and bottom of the semiconductor laser.

By applying a voltage across the p-type ohmic electrode609and the n-type ohmic electrode610to supply a current to the semiconductor laser, the semiconductor laser oscillates and emits a laser beam in a direction of an arrow shown inFIG. 25.

The crystal defects within the semiconductor laser are reduced because the crystal detects of the n-type GaN substrate601are reduced. Consequently, the semiconductor laser can operate for a long serviceable life to produce a large output. In addition, since the GaN substrate601used is the n-type, it is possible to form the ohmic electrode610directly on the GaN substrate601and to reduce the cost, unlike the conventional insulative substrate such as a sapphire substrate which requires two electrodes to be drawn out from the p and n sides via a group III nitride crystal layer which is grown on the sapphire substrate. Moreover, a light emission end surface of the semiconductor laser can be formed by cleaving, when cleaving the chips, thereby making it possible to realize a high-quality semiconductor laser at a low cost.

InFIG. 25, an InGaN MQW is used as the active layer604. However, it is possible to use an AlGaN MQW as the active layer604, so as to shorten the light emission wavelength. In other words, because the crystal defects and impurities in the GaN substrate601are small, light emission from a deep level decreases, and a highly efficient semiconductor laser can be realized even when the light emission wavelength is shortened.

Of course, the use of the GaN substrate is not limited to optical devices such as the semiconductor laser, and the GaN substrate is similarly applicable to electronic devices. In other words, by use of the GaN substrate having the reduced crystal defects, GaN-based layers grown epitaxially on the GaN substrate also have reduced crystal defects. As a result, it is possible to realize a high-performance device by suppressing a leak current and improving the carrier trapping effect when the well structure is employed.

Therefore, high-performance devices can be realized by the use of the group III nitride substrate which is obtained by the method or apparatus of growing the group III nitride crystal. In the case of semiconductor lasers and light emitting diodes, “high-performance” includes high output and long serviceable life which could not be realized conventionally. On the other hand, in the case of electronic devices, “high-performance” includes low power consumption, low noise, high-speed operation and operability under high-temperature conditions. Furthermore, in the case of light receiving devices, “high-performance” includes low noise and long serviceable life.

FIG. 26is a perspective view showing an important part of a second embodiment of the semiconductor device according to the present invention, andFIG. 27is a cross sectional view showing an important part of the semiconductor device shown inFIG. 26cut along a plane perpendicular to a light emitting direction. This embodiment of the semiconductor device uses a GaN substrate which is obtained by any of the above described embodiments of the method of growing the group III nitride crystal or the group III nitride crystal growing apparatus. For the sake of convenience, it is assumed that the GaN substrate used is obtained by the group III nitride crystal growing apparatus shown inFIG. 10.

A semiconductor laser shown inFIGS. 26 and 27has an n-type GaN substrate750which has a thickness of 250 μm and is obtained by the group III nitride crystal growing apparatus shown inFIG. 10. A stacked structure2400shown inFIG. 26includes an n-type GaN layer740, an n-type Al0.2Ga0.8clad layer741, an n-type GaN guide layer742, an In0.05Ga0.95N/In0.15Ga0.85N MQW activation layer743, a p-type GaN guide layer744, a p-type Al0.2Ga0.8N clad layer745and a p-type GaN cap layer746which are successively stacked on the top surface of the n-type GaN substrate750by Metal Organic Chemical Vapor Deposition (MOCVD), as shown inFIG. 27.

The stacked structure2400is etched from the p-type GaN cap layer746to a portion of the p-type Al0.2Ga0.8N clad layer745so that a stripe-shaped portion remains, to thereby form a current-narrowing ridge waveguide structure751. The ridge waveguide structure751is formed along the <1-100> direction of the n-type GaN substrate750, where <1-100> denotes <“1” “1 bar” “0” “0”>. A SiO2insulator layer747is formed on the surface of the stacked structure2400. An opening is formed in the SiO2insulator layer747on a ridge751.

A p-side ohmic electrode748is formed on the surface of the p-type GaN cap layer746which is exposed via this opening in the SiO2insulator layer747. An n-side ohmic electrode749is formed on the bottom surface of the n-type GaN substrate750. The p-side ohmic electrode748and the n-side ohmic electrode749may be formed by vapor deposition of Ni/Au and Ti/Al, respectively.

Optical resonator surfaces2401and2402are formed perpendicularly to the ridge751and the In0.05Ga0.95N/In0.15Ga0.85N MQW activation layer743. The optical resonator surfaces2401and2402are formed by forming a cleavage of a (1-100) face which is perpendicular to the ridge waveguide structure751which extends in the <1-100> direction of the n-type GaN substrate750. The n-side ohmic electrode749and the optical resonator surfaces1401and1402are formed by polishing the bottom surface of the n-type GaN substrate750to a thickness of 80 μm.

By applying a voltage across the p-side ohmic electrode748and the n-side ohmic electrode549, a current flows to inject carriers into the In0.05Ga0.95N/In0.15Ga0.85N MQW activation layer743. As a result, light emission and light amplification occur, and laser beams1411and1412are emitted from respective optical resonator surfaces1401and1402, as indicated by arrows inFIG. 26.

The present inventors confirmed that the semiconductor laser has a long serviceable life even when operated to produce a high output, because the crystal defects in the semiconductor laser of this embodiment is small and the crystal quality of the layers formed on the group III nitride substrate is high, compared to the case where the conventional sapphire substrate or, a GaN substrate which is obtained by the conventional technique such as vapor deposition is used for the semiconductor laser.

FIG. 28is a cross sectional view showing an important part of a third embodiment of the semiconductor device according to the present invention. This embodiment of the semiconductor device uses a GaN substrate which is obtained by any of the above described embodiments of the method of growing the group III nitride crystal or the group III nitride crystal growing apparatus. For the sake of convenience, it is assumed that the GaN substrate used is obtained by the group III nitride crystal growing apparatus shown inFIG. 10.

A light receiving element shown inFIG. 28has an n-type GaN substrate760which has a thickness of 300 μm and is obtained by the group III nitride crystal growing apparatus shown inFIG. 10. An n-type GaN layer761, an insulative GaN layer762, and a transparent Schottky electrode763made of Ni/Au are stacked on the top surface of the n-type GaN substrate760, to form a Metal Insulator Semiconductor (MIS) type light receiving element. An ohmic electrode764made of Ti/Al is formed on the bottom surface of the n-type GaN substrate760. Furthermore, an Au electrode765is formed on a portion of the transparent Schottky electrode763.

When light (ultraviolet ray)2601is received via the transparent Schottky electrode763, carriers are generated to cause a photocurrent to flow via the electrodes765and764.

The present inventors confirmed that the light receiving element has a small dark current and a large signal-to-noise ratio (SNR), because the crystal defects in the light receiving element of this embodiment is small and the crystal quality of the layers formed on the group III nitride substrate is high, compared to the case where the conventional sapphire substrate or, a GaN substrate which is obtained by the conventional technique such as vapor deposition is used for the light receiving element.

FIG. 29is a cross sectional view showing an important part of a fourth embodiment of the semiconductor device according to the present invention. This embodiment of the semiconductor device uses a GaN substrate which is obtained by any of the above described embodiments of the method of growing the group III nitride crystal or the group III nitride crystal growing apparatus. For the sake of convenience, it is assumed that the GaN substrate used is obtained by the group III nitride crystal growing apparatus shown inFIG. 10.

A High Electron Mobility Transistor (HEMT) shown inFIG. 29forms an electronic device having a high-resistance GaN substrate770which has a thickness of 300 μm and is obtained by the group III nitride crystal growing apparatus shown inFIG. 10. An insulative GaN layer771, an n-type AlGaN layer772, and an n-type GaN layer773are stacked on the top surface of the high-resistance GaN substrate770, so as to form a recess gate type HEMT. A gate portion of the n-type GaN layer773is etched to the n-type AlGaN layer772, and a gate electrode776made of Ni/Au is formed on the exposed n-type AlGaN layer772. A drain electrode775made of Ti/Al and a source electrode774made of Ti/Al are formed on the n-type GaN layer773on respective sides of the gate electrode776.

The present inventors confirmed that the HEMT has suppressed abnormal diffusion and short-circuiting of the electrode which are caused by crystal defects, high withstand voltage and satisfactory frequency characteristics, because the crystal defects in the HEMT of this embodiment is small and the crystal quality of the layers formed on the group III nitride substrate is high, compared to the case where the conventional sapphire substrate or, a GaN substrate which is obtained by the conventional technique such as vapor phase deposition is used for the HEMT.

FIG. 30is a diagram showing an illumination apparatus using a fifth embodiment of the semiconductor device according to the present invention, andFIG. 31is a circuit diagram showing the illumination apparatus shown inFIG. 30.FIG. 32is a cross sectional view showing a white LED module within the illumination apparatus shown inFIG. 30, andFIG. 33is a cross sectional view showing an important part of the fifth embodiment of the semiconductor device within the white LED module.

The illumination apparatus shown inFIGS. 30 and 31includes two white LED modules1902, a current limiting resistor796, a current source797and a switch798which are connected in series. The white LED modules1902are turned ON or OFF by switching the switch798to the ON or OFF state.

As shown inFIG. 32, each white LED module1902has a YAG fluorescent material791coated on an ultraviolet LED790. When a predetermined voltage is applied across electrode terminals794and795, the ultraviolet LED790emits ultraviolet ray which excites the YAG fluorescent material791such that white light1901is emitted via the YAG fluorescent material791. The white light1901is indicated by arrows inFIGS. 30 and 32.

The ultraviolet LED790shown inFIG. 33has an n-type GaN substrate780which has a thickness of 300 μm and is obtained by the group III nitride crystal growing apparatus shown inFIG. 10. An n-type GaN layer781, an n-type Al0.1Ga0.9N layer782, an activation layer783having an InGaN/GaN MQW structure, a p-type Al0.1Ga0.9N layer784, and a p-type GaN layer785are stacked on the top surface of the n-type GaN substrate780. A transparent ohmic electrode786made of Ni/Au is formed on the p-type GaN layer785. An electrode787made f Ni/Au and provided for wire-bonding is formed on the transparent ohmic electrode786. In addition, an ohmic electrode788made of Ti/Al is formed on the bottom surface of the n-type GaN substrate780.

By applying a voltage across the p-side electrode787and the n-side ohmic electrode788, a current flows to inject carriers into the activation layer783. As a result, light emission occurs, and ultraviolet ray1801is emitted from the ultraviolet LED790, as indicated by an arrow inFIG. 33.

The present inventors confirmed that the LED has a high light emission efficiency and is capable of producing a high output, because the crystal defects in the LED of this embodiment is small and the crystal quality of the layers formed on the group III nitride substrate is high, compared to the case where the conventional sapphire substrate or, a GaN substrate which is obtained by the conventional technique such as vapor phase deposition is used for the LED.

In addition, it was confirmed that the illumination apparatus using the above LED is brighter but has a low power, compared to the case where the conventional sapphire substrate or, a GaN substrate which is obtained by the conventional technique such as vapor phase deposition is used for the LED of the illumination apparatus.

Therefore, according to the embodiments of the semiconductor device, it is possible to realize high-performance semiconductor devices based on the group III nitride substrate grown by the method or apparatus of the present invention, by providing a light emitting structure, a light receiving structure, a transistor structure and the like on the group III nitride substrate. In this case, the light emitting structure may form a light emitting diode, a laser diode (semiconductor laser) and the like. The light receiving structure may form a photoconductor cell, a pn-junction photodiode, a hetero-junction photodiode, a hetero-junction bipolar phototransistor and the like. The light receiving element may be used for a fire alarm sensor, a wavelength selection type detector and the like. In addition, the transistor structure may form a Field Effect Transistor (FET), a Heterojunction Bipolar Transistor (HBT), HEMT and the like. Of course, other electronic devices may be formed on the group III nitride substrate, such as high-temperature operating devices which operate at high temperatures, high-frequency devices which operate at high frequencies, and electronic devices which produce a large output or operate under a large power.