Multi-beam semiconductor laser element

A multi-beam semiconductor laser device capable of emitting respective laser beams with uniform optical output levels and enabling easy alignment is provided. This multi-beam semiconductor laser device (40) is a GaN base multi-beam semiconductor laser device provided with four laser stripes (42A, 42B, 42C and 42D) which are capable of emitting laser beams with the same wavelength. The respective laser oscillating regions (42A to 42D) are provided with a p-type common electrode (48) on a mesa structure (46) which is formed on a sapphire substrate (44), and have active regions (50A, 50B, 50C and 50D) respectively. Two n-type electrodes (52A and 52B) are provided on an n-type GaN contact layer (54) and located as common electrodes opposite to the p-type common electrode (48) on both sides of the mesa structure (46). The distance A between the laser stripe (42A) and the laser stripe (42D) is no larger than 100 μm. The distance B1 between the laser stripe (42A) and the n-type electrode (52B) is no larger than 150 μm while the distance B2 between the laser stripe (42D) and the n-type electrode (52A) is no larger than 150 μm.

FIELD OF THE INVENTION

The present invention relates to a multi-beam semiconductor laser device which is provided with a plurality of laser oscillating regions in the form of stripes and capable of emitting a laser beam from each laser oscillating region thereof, and in particular relates to a multi-beam semiconductor laser device which is made of a gallium nitride (GaN) III-V group compound semiconductor.

BACKGROUND OF THE INVENTION

Multi-Beam Semiconductor Laser Device

In recent years, there is a demand for the increase in the operation speed and the capacity of an optical disc device, a laser beam printer, a copying machine and the like device making use of a semiconductor laser as a light source. To meet the demand for the increase in the operation speed and the capacity, it has been proposed to utilize a multi-beam semiconductor laser capable of emitting a plurality of laser beams (referred to as multiple beams in the following explanation) as a light source. For example, in the case of an optical disc device, it is possible to increase the read rate thereof by reading data from a plurality of tracks with a plurality of laser beams at the same time by the use of a multi-beam semiconductor laser.

On the other hand, while the optical output level required of the light source of an optical disc device is only several tens of mW at most, a semiconductor laser device can be used in the field of laser processing technologies and in the field of medicine by increasing the optical output level thereof to the order of W. Accordingly, the multi-beam semiconductor laser study is in works to increase the total optical output level of laser light.

Next, with reference to FIG.10andFIG. 11, the configuration of a prior art multi-beam semiconductor laser device is explained.

The multi-beam semiconductor laser device10as illustrated inFIG. 10is capable of emitting two laser beams, and composed of two laser oscillating regions14A and14B sharing a common substrate12, and provided with electrodes16A and16B respectively on the laser oscillating regions14A and14B. An opposite electrode17located opposed to the electrodes16A and16B is provided on the rear surface of the substrate12as a common electrode.

Furthermore, the multi-beam semiconductor laser device10is provided with two contact electrodes18A and18B to be in contact with the electrodes16A and16B respectively, and a base substrate22provided with wiring patterns20A and20B with which the contact electrodes18A and18B are connected to external terminals, wherein the electrodes16A and16B are electrically and mechanically connected to the contact electrodes18A and18B in the form of an integrated multi-beam semiconductor laser device configuration.

The multi-beam semiconductor laser device24as illustrated inFIG. 11is capable of emitting four laser beams, and composed of four laser oscillating regions28A,28B,28C and28D sharing a common substrate26, and provided with electrodes30A,30B,30C and30D respectively on the laser oscillating regions28A to28D. An opposite electrode31located opposed to the electrodes30A to30D is provided on the rear surface of the substrate26as a common electrode. Furthermore, the multi-beam semiconductor laser device24is provided with four contact electrodes32A,32B,32C and32D to be in contact with the electrodes30A to30D respectively, and a base substrate36provided with wiring patterns34A,34B,34C and34D with which the contact electrodes32A to32D are connected to external terminals, wherein the electrodes30A to30D are electrically and mechanically connected to the contact electrodes32A to32D in the form of an integrated multi-beam semiconductor laser device configuration.

GaN Base Semiconductor Laser Device Fabricated By Using The ELO Technique

On the other hand, in the field of optical memories, there is a need for a semiconductor laser device capable of emitting short-wavelength light in order to increase the recording density of an optical recording medium such as an optical disc. To meet it, research is actively carried out into gallium nitride (GaN) III-V group compound semiconductors (referred to as GaN base compound semiconductors in the following description.

A GaN base semiconductor laser device is composed generally of a laminate structure grown on a substrate. Since the device characteristics of a GaN base compound semiconductor device are affected by the crystalline condition of a GaN base compound semiconductor layer grown on a substrate, it is required for the purpose of good device characteristics to form the laminate structure of the GaN base compound semiconductor in which a few crystal defects exist.

However, since no appropriate substrate has been found which can provide a good lattice match with a GaN semiconductor as a base substrate on which a GaN base compound semiconductor layer is grown, a sapphire (α·Al2O3) substrate has been used for this purpose while the lattice constants of a sapphire substrate and a GaN layer are different from each other resulting in lattice mismatch, and in addition to this, the coefficients of thermal expansion are largely different from each other.

When a substrate provides only a poor lattice match with a GaN base compound semiconductor layer, there is generated a substantial strain within the GaN base compound semiconductor layer grown on the substrate, and therefore the crystallinity suffers from various adverse effects. For example, in order to lessen the strain as generated, a large amount of dislocations are generated in the GaN base compound semiconductor layer on the sapphire substrate with a density of the order of 108cm−2to 1010cm−2.

The dislocations include threading dislocations which propagate in the thickness direction of the GaN base compound semiconductor layer, reach an active layer formed in the GaN base compound semiconductor layer, and become detrimental crystal defects which function as current leakage paths, non-light-emitting centers, and so forth to deteriorate the electric and optical characteristics of the device. Accordingly, the generation of threading dislocations has to be minimized in order to fabricate a GaN base semiconductor device having good device characteristics. From this view point, in recent years, ELO (Epitaxial Lateral Overgrowth) techniques are developed as an effective technique to lessen the generation of threading dislocations by the use of epitaxial growth in the lateral direction.

The ELO techniques are generally classified into two types, i.e., mask-using ELO techniques and free-standing ELO techniques (referred to as FS-ELO techniques in the following description).

In accordance with an FS-ELO technique, after growing a GaN base layer on a sapphire substrate, a concavo-convex stripe pattern is formed on the GaN base layer by etching the GaN base layer, for example, by reactive ion etching (RIE). The concavo-convex stripe pattern is formed as a concavo-convex structure in the form of stripes including concave areas formed by removing the GaN base layer and the most upper surface portion of the substrate to expose the substrate, and convex portion formed by the GaN base layer on the upper surface of the substrate. Next, in accordance with the technique, a GaN layer is epitaxial grown on the concavo-convex structure in the upper direction while the epitaxial grown GaN layer is further grown in the lateral direction to fill the concave areas. The dislocation density has been evaluated to be low in an area formed by epitaxial growth in the lateral direction (referred to as a wing area in the following explanation).

In the following description, the growth in the lateral direction by the FS-ELO technique will be explained together with the shortcomings thereof in further detail with reference toFIG. 16Ato FIG.16C and FIG.17A and FIG.17B.

First, as illustrated inFIG. 16A, a GaN layer174is formed on a sapphire substrate172. Since there are lattice mismatch and thermal mismatch between the sapphire substrate172and the GaN layer174, a high density defective region176is formed in the GaN layer174adjacent to the substrate as shown in FIG.16B.

Meanwhile, in the case where a buffer layer of GaN, AlN or the like is formed on the sapphire substrate172in advance of forming the GaN layer174, the high density defective region176of the buffer layer is formed in the vicinity of the sapphire substrate172.

More specifically speaking, the seed defects as generated in the high density defective region176include stacking defects, dislocation loops having components extending approximately in parallel to the crystal growth plane, and threading dislocations extending approximately in parallel to the growth direction. Among them, the threading dislocations extending approximately in parallel to the growth direction furthermore extend from the high density defective region176into the GaN layer174.

Next, after forming a mask in the form of stripes (not shown in the figure) on the GaN layer174, a concavo-convex structure is formed on the surface of the substrate as illustrated inFIG. 16Cby etching the GaN layer174and the upper portion of the sapphire substrate172. In the following explanation, the convex portion is referred to as a seed crystal area178.

Next, after removing the mask formed on the seed crystal areas178by chemical etching or the like, a second GaN layer180is grown on the upper portion of the seed crystal areas178, while growing between the seed crystal areas178as the wing areas182by epitaxially growing the second GaN layer180under such a growth condition that it is grown mainly in the lateral direction as illustrated in FIG.17A. When the wing areas182are formed by the second GaN layer180, a vacant space184is formed between the second GaN layer180and the sapphire substrate172.

In this case, crystal defects are generated within the wing areas182during the growth in the lateral direction when the second GaN layer180is formed. Namely, as illustrated inFIG. 17B, dislocations186A and186B are formed from the high density defective region176in order to propagate approximately in parallel to the substrate while, among these dislocations, the dislocations186A are bended at a meeting location188and extended in the vertical direction therefrom. Also, the dislocation186B is bended in the vicinity of the meeting location188and extended in the vertical direction. Furthermore, threading dislocations190are observed which are extended through the seed crystal area178in the thickness direction of the second GaN layer180from the high density defective region176.

As explained in the above, while high density defective region are generated above the seed crystal areas178and the intermediate location between adjacent seed crystal areas178, low density defective regions are regions of the wing areas182as located between the meeting location188and the respective seed crystal area178. Accordingly, the high density defective regions and the low density defective regions are periodically located corresponding to the periodical arrangement of the seed crystal areas.

First Object of the Present Invention

On the other hand, there are the following problems of the multi-beam semiconductor laser device in accordance with the conventional technique as illustrated in FIG.10and FIG.11.

The first problem is that it is difficult to apply the configuration of the prior art multi-beam semiconductor laser device to a semiconductor laser device, such as a GaN base semiconductor laser device, which is provided with a p-type electrode and an n-type electrode in the same side of the substrate.

The second problem is that, in the case of a GaN base semiconductor laser device, which is provided with a p-type electrode and an n-type electrode in the same side of the substrate, it is difficult to fabricate a multi-beam semiconductor laser device capable of emitting respective laser beams with uniform optical output levels.

The third problem is that since each electrode on the laser oscillating region is connected to the corresponding contact electrode, it is extremely difficult to align these electrodes with each other in the case where the interval between the respective laser oscillating regions becomes narrow.

In other words, since the interval between the respective laser oscillating regions and the interval between the respective contact areas are small, one contact electrode can be connected to two laser oscillating regions only when the location of the contact electrode is slightly displaced with respect to the electrodes of the laser oscillating regions. As a result, the device yield of the multi-beam semiconductor laser device will drop. Accordingly, it is difficult in practice to increase the optical output level by increasing the number of laser beams.

It is therefore the first object of the present invention to provide a multi-beam semiconductor laser device in which the optical output levels of the respective beams are equal to each other while alignment is easy.

Second Object of the Present Invention

While the multi-beam semiconductor laser study is in works to increase the total optical output level of laser light as described above, the laser characteristics tend to be degraded while the device life cycle is shortened if a laser oscillating region is arranged on a high density defective region where crystal defects are generated due to dislocations when a multi-beam semiconductor laser is fabricated by the ELO method.

However, unless the location of a laser oscillating region has been determinate with respect to high density defective regions and low density defective regions, the attempt to locate a laser oscillating region above a low density defective region ends up in failure. From this fact, it is difficult to fabricate a multi-beam semiconductor laser device having good laser characteristics, a high optical output level and a long device life cycle.

Accordingly, the second object of the present invention is to provide a multi-beam semiconductor laser device having good laser characteristics and a high optical output level.

DISCLOSURE OF THE INVENTION

First Invention for Accomplishing the First Object:

In order to accomplishing the first object as described above, a multi-beam semiconductor laser device in accordance with the present invention (referred to as the first invention in the following description) has a common substrate provided with a mesa structure on which a plurality of laser oscillating regions are fabricated in the form of stripes, and comprises: a first electrode provided for each of the plurality of laser oscillating regions for functioning as one of a p-type electrode and an n-type electrode of each laser oscillating region; and a second electrode located aside of the mesa structure on the common substrate as a common electrode to at least two of the plurality of the laser oscillating regions for functioning as the other of the p-type electrode and the n-type electrode of each of the two laser oscillating regions and as an opposite electrode to the first electrode.

The above described first electrode may be separately provided for each laser oscillating region, or alternatively may be provided as a common electrode to the respective laser oscillating regions.

In the case of the multi-beam semiconductor laser device in accordance with the first invention, it is easy to adjust the alignment of electrodes, when mounting on a sub mount, by designing the p-type electrode as a common electrode and the n-type electrode as a common electrode.

Also, the second electrode may be provided on the both sides of the mesa structure as common opposite electrodes to the above described first electrode, alternatively may be provided between adjacent mesa structures as a common opposite electrode.

Preferably, the following equations are satisfied.
A≦100 μm
B≦150 μm
where A is a distance between one of the laser oscillating regions closest to an edge of the common electrode aside of the laser oscillating regions and another of the laser oscillating regions farthest from the edge of the common electrode; and B is a distance between another of the oscillating regions farthest from the edge of the common electrode and the edge of the common electrode aside of the laser oscillating regions.

In this case, the one of the laser oscillating regions closest to the edge of the common electrode and the another of the oscillating regions farthest from the edge of the common electrode for defining A and B are laser oscillating regions which share the same common electrode. For example, in the case where a common electrode is provided on each of the both sides of the plurality of laser oscillating regions, A and B are defined by those of the plurality of the laser oscillating regions that are substantially sharing one common electrode while A and B are furthermore defined by the remainder of the plurality of the laser oscillating regions that are substantially sharing the other common electrode.

The numerical values determining the ranges of the above described A and B have been based on the results of experiments and the result of simulation with either of the above described common electrodes.

For example, if B exceeds 150 μm when the driving current is 50 mA, the voltage drop between the above described farthest laser oscillating region and the common electrode increases, for example, to exceed 0.05 V and therefore it is difficult to emit respective laser beams from a plurality of laser oscillating regions with uniform optical output levels.

In the case of the multi-beam semiconductor laser device in accordance with the first invention, laser oscillating regions are provided with one electrode of a p-type electrode and an n-type electrode as a first electrode on a mesa structure formed on a common substrate, while a second electrode of the other electrode of the p-type electrode and the n-type electrode is provided aside of the mesa structure as a common electrode opposite to the first electrode, and therefore the optical output levels of the respective laser oscillating regions becomes high and uniform.

The multi-beam semiconductor laser device in accordance with the first invention is applicable irrespective of the composition of a substrate and the composition of a compound semiconductor layer forming a laser structure, for example, is preferably applicable to a GaN base semiconductor laser device.

A GaN base semiconductor laser device is a semiconductor laser device comprising a sapphire substrate or a GaN substrate on which is formed an AlaBbGacIndN (a+b+c+d=1 and 0≦a,b,c,d≦1) film as a constituent layer.

When the first invention is applied, there is no restriction on the structure of a light waveguide so that the first invention is applicable to refractive index guided structures and also applicable to gain guided structures. Furthermore, there is no restriction on the structure of a laser oscillating region so that the first invention is applicable to air-ridge types, buried ridge types and so forth.

Still further, there is no restriction on the current confinement structure so that the first invention is applicable to a current confinement structure by the use of an insulating film, a high resistance layer, separation of a PN junction and so forth.

Also, the multi-beam semiconductor laser device in accordance with the first invention is suitable as a device to be mounted on the sub mount in a junction down fashion, and in this case, it is connected to a sub mount which is provided with a first junction electrode to be electrically connected to the above described one electrode and a second junction electrode to be electrically connected to the above described electrode.

Second to Fifth Inventions for Accomplishing the Second Object:

In order to accomplishing the second object, the inventor of the present invention has obtained the results as illustrated inFIG. 18by investigating the defect density (EPD; Etch Pit Density) of a substrate within which are formed high density defective regions originating from seed crystal areas and meeting locations and low density defective regions each of which is located between adjacent ones of the seed crystal areas and the meeting locations, the high density defective regions and the low density defective regions being periodically and alternately arranged in parallel with each other in the form of stripes.

Namely, the defect density reached 5×108cm−2in the location over and near a seed crystal area while the defect density reached 1×108cm−2in a meeting location. However, in the location 0.5 μm or more distant from the seed crystal area and the meeting location, the defect density failed to 105cm−2, and therefore it was confirmed that the location could be considered as a low density defective region.

Accordingly, it is possible to fabricate a multi-beam semiconductor laser device having good laser characteristics by arranging laser oscillating regions in low density defective regions which are 0.5 μm or more distant from seed crystal areas and meeting locations.

Also, since a conventional semiconductor laser device with an output level in the order of W has one laser oscillating region from which a laser light is emitted at a high optical output level without causing destruction of the end surface thereof, the width of the laser oscillating region is 50 μm to 100 μm.

In this case, since the maximum interval of seed crystal areas is 18 μm or thereabout, the laser oscillating region is formed over seed crystal areas and meeting locations which are high density defective regions, and therefore the laser characteristics tend to be degraded while the device life cycle is shortened On the other hand, if adjacent seed crystal areas are arranged apart from each other by an interval of 18 μm or wider, a GaN base compound semiconductor layer can not sufficiently be grown in the lateral direction from the seed crystal areas.

Accordingly, the inventor of the present invention come up with the idea that a high reliability semiconductor laser device having good laser characteristics, a high optical output level and a long device life cycle could be realized by providing a plurality of narrow laser oscillating regions located in low density defective regions respectively, and culminated the present invention after repeating various experiments.

Second Invention

In order to accomplishing the second object as described above, taking into consideration the above idea, a multi-beam semiconductor laser device in accordance with the present invention (referred to as the second invention in the following description) has a common substrate within which are formed high density defective regions originating from seed crystal areas and meeting locations and low density defective regions each of which is located between adjacent ones of the seed crystal areas and the meeting locations, the high density defective regions and the low density defective regions being periodically and alternately arranged in parallel with each other in the form of stripes; and a plurality of laser oscillating regions formed on the common substrate and capable of emitting laser beams respectively, wherein each of the laser oscillating regions is located in a different one of the low density defective regions, and wherein
X1≧0.5 μm
X2≧0.5 μm
where X1is a distance between each of the laser oscillating regions and one of the seed crystal areas, and X2is a distance between each of the laser oscillating regions and one of the meeting locations.

The limitations of X1≧0.5 μm and X20.5 μm of the second invention are based upon the experimental results as described above.

The same is applied to the third to fifth inventions as follows.

Third Invention

Another multi-beam semiconductor laser device in accordance with the present invention (referred to as the third invention in the following description) has a common substrate within which are formed high density defective regions originating from seed crystal areas and meeting locations and low density defective regions each of which is located between adjacent ones of the seed crystal areas and the meeting locations, the high density defective regions and the low density defective regions being periodically and alternately arranged in parallel with each other in the form of stripes; and a plurality of laser oscillating regions formed on the common substrate and capable of emitting laser beams respectively, wherein the laser oscillating regions are located in the low density defective regions which are arranged adjacent to each other with the seed crystal areas and the meeting locations inbetween, and wherein
X1≧0.5 μm
X2≧0.5 μm
where X1is a distance between one of the laser oscillating regions and one of the seed crystal areas, and X2is a distance between one of the laser oscillating regions and one of the meeting locations.

In the case of the multi-beam semiconductor laser device in accordance with the third invention, a plurality of laser oscillating regions may be arranged in each low density defective region with a seed crystal area or a meeting location inbetween respectively. Also, the number of laser oscillating regions arranged in one low density defective region may be different than the number of laser oscillating regions in an adjacent low density defective region.

Fourth Invention

A further multi-beam semiconductor laser device in accordance with the present invention (referred to as the fourth invention in the following description) has a common substrate within which are formed high density defective regions originating from seed crystal areas and meeting locations and low density defective regions each of which is located between adjacent ones of the seed crystal areas and the meeting locations, the high density defective regions and the low density defective regions being periodically and alternately arranged in parallel with each other in the form of stripes; and a plurality of laser oscillating regions formed on the common substrate and capable of emitting laser beams respectively, wherein at least two of the laser oscillating regions are located in each of the low density defective regions, and wherein
X1≧0.5 μm
X2≧0.5 μm
where X1is a distance between one of the laser oscillating regions and one of the seed crystal areas, and X2is a distance between one of the laser oscillating regions and one of the meeting locations.
Fifth Invention

A still further multi-beam semiconductor laser device in accordance with the present invention (referred to as the fifth invention in the following description) has a common substrate within which are formed high density defective regions originating from seed crystal areas and meeting locations and low density defective regions each of which is located between adjacent ones of the seed crystal areas and the meeting locations, the high density defective regions and the low density defective regions being periodically and alternately arranged in parallel with each other in the form of stripes; and a plurality of laser oscillating regions formed on the common substrate and capable of emitting laser beams respectively, wherein the laser oscillating regions are located on every other region of the low density defective regions, and wherein
X1≧0.5 μm
X2≧0.5 μm
where X1is a distance between one of the laser oscillating regions and one of the seed crystal areas, and X2is a distance between one of the laser oscillating regions and one of the meeting locations.

In the case of the multi-beam semiconductor laser devices in accordance with the second to fifth inventions, the respective laser oscillating regions may be capable of emitting laser light of different wavelengths and/or at different output power levels.

Also, in the case of the multi-beam semiconductor laser devices in accordance with the second to fifth inventions, there is no restriction on the fabrication process of a substrate as long as the substrate comprises high density defective regions originating from seed crystal areas and meeting locations and low density defective regions each of which is located between adjacent ones of the seed crystal areas and the meeting locations, the high density defective regions and the low density defective regions being periodically and alternately arranged in parallel with each other in the form of stripes. Furthermore, basically, while there is no restriction on the composition of a GaN base compound semiconductor layer constituting a laser structure, the present invention may be best suited for a GaN base laser structure.

In this case, a GaN base compound semiconductor is represented by AlaBbGacIndN (a+b+c+d=1 and 0≦a,b,c,d≦1).

When any of the second to fifth inventions is applied, there is no restriction on the configuration of the waveguide, so that the invention is applicable to refractive index guided structures and also applicable to gain guided structures. Furthermore, there is no restriction on the structure of a laser oscillating region so that the invention is applicable to air-ridge types, buried ridge types and so forth. Also, there is no restriction on the current confinement structure so that the invention is applicable to a current confinement structure by the use of an insulating film, a high resistance layer, separation of a PN junction and so forth.

Third Object of the Present Invention

Meanwhile, when the multi-beam semiconductor laser device in accordance with the first invention was being developed, the following points were realized.

Since nitride base semiconductor laser devices are fabricated, in many cases, on sapphire substrates which are made of an insulating material, an n-type electrode and a p-type electrode are usually formed in the laminate structure of compound semiconductors and located opposite to the sapphire substrate in the form of a resonating structure.

For example, in the case of a nitride base multi-beam semiconductor laser device250as illustrated inFIG. 24, a plurality of laser oscillating regions252A,252B,252C and252D are laterally arranged in parallel on a common mesa structure253and provided with electrodes (referred to as stripe electrodes for the sake of clarity in explanation)254A,254B,254C and254D for the respective laser oscillating regions252A to252D and common n-type electrodes256A and256B which are formed on an n-type contact layer257in the laminate structure opposite to the sapphire substrate258.

Then, the distances from the respective stripe electrodes254A to254D to the common n-type electrode256A or256B are different from each other. For this reason, the remoter the laser oscillating region is located from the common n-type electrode256A or256B, the longer the current path between the n-type electrode and the p-type electrode become, resulting in a higher electric resistance.

As a result, the amounts of current as injected to the respective stripe electrodes254A to254D are different from each other laser oscillating region so that the remoter the laser oscillating region is located from the n-type electrode, the weaker the luminescence intensity of light emitted from the laser oscillating region as illustrated in FIG.25.

In this manner, in the case of a multi-beam semiconductor laser device having dispersed luminescence intensities of laser oscillating regions, the laser oscillating region capable of emitting a higher intensity beam tends to quickly deteriorate and therefore the device life cycle of the multi-beam semiconductor laser device is shorter than that of a multi-beam semiconductor laser device capable of emitting uniform laser beams.

Sixth Invention for Accomplishing the Third Object:

It is therefore the third object of the present invention to provide a multi-beam semiconductor laser device in which the luminescence intensities of the respective beams are uniform.

In order to accomplishing the third object as described above, a multi-beam semiconductor laser device in accordance with the present invention (referred to as the sixth invention in the following description) has a common substrate provided with a mesa structure on which a plurality of laser oscillating regions are fabricated in the form of stripes, the multi-beam semiconductor laser device comprising: a first electrode (stripe electrodes) provided for each of the plurality of laser oscillating regions for functioning as one of a p-type electrode and an n-type electrode of the laser oscillating region; and a second electrode located aside of the mesa structure on the common substrate as a common electrode to at least two of the plurality of the laser oscillating regions for functioning as the other of the p-type electrode and the n-type electrode of each of the two laser oscillating regions and as an opposite electrode to the first electrode, wherein the plurality of the stripe electrodes of the first electrode have different areas corresponding to the distances thereof from the common electrode in order to flow a substantially same current from the stripe electrodes of the first electrode.

In the case of the multi-beam semiconductor laser device in accordance with the sixth invention, the luminescence intensities of the respective location of the laser oscillating regions are made uniform by changing the areas of the first electrodes in accordance with the distance therefrom to the common electrode in order to make equal the respective electric resistances between the respective first electrodes and the common electrode and to flow the same current between the respective first electrodes and the common electrode.

In the case of a specific embodiment of the sixth invention wherein n laser oscillating regions are provided with a first electrode in the form of stripe electrodes respectively and joined to a common electrode located aside of a mesa structure, the following equation is satisfied
(ρv·d)/S(i)+rsh·(l(i)/L)=C(constant value)  (Equation 1)
where ρv is an effective specific resistance in the longitudinal direction from the first electrode through the active layer; d is an effective thickness in the longitudinal direction from the first electrode to the common electrode through the active layer; rsh is a sheet resistance from the first electrode to the common electrode; L is a resonator length of the laser oscillating regions; S(i) is the area of the first electrode of i-th (i=1, 2, . . . n) laser oscillating region (i) of the laser oscillating regions; l(i) is a distance in the lateral direction from the center of the laser oscillating region (i) to the common electrode.

In the case of a specific embodiment of the sixth invention wherein n laser oscillating regions are provided with the first electrode in the form of stripe electrodes respectively and joined to first and second common electrodes located on both sides of a mesa structure, the following equation is satisfied
(ρv·d)/S(i)+rsh·A(i)·(1/L)=C(constant value)
A(i)=(lN(i)·lF(i))/(lN(i)+lF(i))  (Equation 2)
where ρv is an effective specific resistance in the longitudinal direction from the first electrode through the active layer; d is an effective thickness in the longitudinal direction from the first electrode to the first and equivalently second common electrode through the active layer; rsh is a sheet resistance from the first electrode to the first and equivalently second common electrode; L is a resonator length of the laser oscillating regions; S(i) is the area of the stripe electrode of the first electrode of i-th (i=1, 2, . . . n) laser oscillating region (i) of the laser oscillating regions; lN(i) is a distance in the lateral direction from the center of the laser oscillating region (i) to one of the common electrode near to the center of the laser oscillating region (i); lF(i) is a distance in the lateral direction from the center of the laser oscillating region (i) to one of the common electrode remote from the center of the laser oscillating region (i).

In the case of the two examples as described above of the embodiment of the sixth invention, it is possible to make equal the respective electric resistances between the respective first electrodes and the common electrode and to flow the same current between the respective first electrodes and the common electrode by designing the areas S(i) of the first electrode as described above. Alternatively, the product W(i)·L of the width W(i) of the first electrode of the laser oscillating region (i) and the resonator length L of the laser oscillating region (i) may be changed for the same purpose as the area S(i).

In the case of the multi-beam semiconductor laser device in accordance with the sixth invention wherein the laser oscillating region thereof has the constant width in the longitudinal direction, the invention is not limited thereto but also applicable to the case where at least one edge of at least one of a plurality of laser oscillating regions is tapered in a plan view.

The effective thickness d in the longitudinal direction from the first electrode to the common electrode through the active layer and the effective thickness d in the longitudinal direction from the first electrode to the first and second common electrodes through the active layer can be recognized as the height of the common mesa structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the followings, various embodiments of the present invention will be specifically and detailedly described with reference to the accompanying drawings. Meanwhile, the film formation process, the compositions and the film thicknesses of compound semiconductor layers, the ridge widths, the process conditions and so forth as described in the explanation of the following embodiments are merely illustrative instead of limiting on the present invention.

First Embodiment of the First Invention

The present embodiment is related to a specific example of a multi-beam semiconductor laser device in accordance with the first invention.FIG. 1is a schematic cross section view showing the overall configuration of this multi-beam semiconductor laser device.FIG. 2is a cross section view showing the configuration of a part thereof.

The multi-beam semiconductor laser device40in accordance with the present embodiment is a GaN base multi-beam semiconductor laser device, as illustrated inFIG. 1, provided with four laser oscillating regions42A,42B,42C and42D in the form of stripes which are capable of emitting laser beams with the same wavelength.

The laser oscillating regions42A to42D are provided with a p-type common electrode48on a mesa structure46which is formed on a sapphire substrate44, and have active regions50A, SOB,50C and50D respectively. Also, two n-type electrodes52A and52B are provided on an n-type GaN contact layer54and located as common electrodes opposite to the p-type common electrode48on both sides of the mesa structure46.

The width W of the mesa structure46in the direction parallel to the sapphire substrate44is 250 μm while the distance A between the laser oscillating region42A and the laser oscillating region42D is 200 μm. The distance A1between the laser oscillating region42A and the laser oscillating region42B is 16 μm while the distance A2between the laser oscillating region42C and the laser oscillating region42D is 16 μm. Also, the distance B1between the laser oscillating region42B and the edge of the n-type electrode52A just adjacent to the mesa structure46is 76 μm while the distance B2between the laser oscillating region42C and the edge of the n-type electrode52B just adjacent to the laser oscillating region is 76 μm.

The distance between the laser oscillating region42A and the edge of the n-type electrode52B just adjacent to the laser oscillating region is 260 μm while the distance between the laser oscillating region42A and the edge of the n-type electrode52A just adjacent to the laser oscillating region is 60 μm. Furthermore, the distance between the laser oscillating region42D and the edge of the n-type electrode52A just adjacent to the laser oscillating region is 260 μm while the distance between the laser oscillating region42D and the edge of the n-type electrode52B just adjacent to the laser oscillating region is 60 μm.

In accordance with the present embodiment, the interval between the laser oscillating region42B and the laser oscillating region42C is larger than the interval between the laser oscillating region42A and the laser oscillating region42B and larger than the laser oscillating region42C and the laser oscillating region42D. This is only for the purpose of facilitating the test procedure of the multi-beam semiconductor laser device40while it is not requisite to make relatively wider the interval between the laser oscillating region42B and the laser oscillating region42C but it is possible to make the interval equal to the interval between the other laser oscillating regions.

The laser oscillating region42A is an air-ridge type laser oscillating region in which current is confined by an SiO2film70as illustrated inFIG. 2. AGaN seed crystal layer56, an n-type GaN contact layer54, an n-type AlGaN cladding layer58, an n-type GaN light guide layer60, an active layer62, a p-type GaN light guide layer64, a p-type AlGaN cladding layer66and a p-type GaN contact layer68are sequentially laminated on the C-plane of the sapphire substrate44in a laminate structure. Meanwhile, not shown in the figure, a GaN buffer layer may be grown at a low temperature between the sapphire substrate44and the GaN seed crystal layer56.

The upper portion of the p-type AlGaN cladding layer66constituting the laser oscillating region42A and the p-type GaN contact layer68are extending in the form of a ridge stripe in one direction. Also, the upper portion of the n-type GaN contact layer54and the n-type AlGaN cladding layer58, the n-type GaN light guide layer60, the active layer62, the p-type GaN light guide layer64and the lower portion of the p-type AlGaN cladding layer66are formed as the mesa structure46extending in the same direction as the laser oscillating region42A is extending. Meanwhile, the mesa structure46is formed as a common mesa structure of the laser oscillating region42A to42D. In other words, the n-type GaN contact layer54, the n-type AlGaN cladding layer58, the n-type GaN light guide layer60, the active layer62, the p-type GaN light guide layer64and the p-type AlGaN cladding layer66are formed as a common laminate structure to the respective laser oscillating region42A to42D.

Furthermore, the GaN seed crystal layer56is formed as a concavo-convex structure extending in the same direction as the laser oscillating region42A and the mesa structure46are extending while the laser oscillating region42A is located between two concave portions of the concavo-convex structure.

The laser oscillating region42A to42D, the mesa structure46and the n-type GaN contact layer54adjacent to the mesa structure46are coated with the SiO2film70except for the upper surface of the laser oscillating region42A to42D and some surface portions of the n-type GaN contact layer54.

A p-type common electrode48made of a multi-layered metallic film such as a Pd/Pt/Au electrode is formed over the respective p-type GaN contact layer68, as a common ohmic junction electrode to the respective laser oscillating region42A to42D, by laminating palladium (Pt), platinum (Pt) and gold (Au) in this order through openings of the SiO2film70.

Also, n-type electrodes52A and52B made of a multi-layered metallic film such as a Ti/Al/Pt/Au electrode is formed on the n-type GaN contact layer54on both sides of the mesa structure46, as a common ohmic junction electrode to the respective laser oscillating region42A to42D, by laminating titanium (Ti), aluminum (Al), platinum and gold in this order through openings of the SiO2film70. However, because of the respective distances between the laser oscillating regions42A to42D and the n-type electrodes52A and52B, the n-type electrode52A mainly serves as the common electrode to the laser oscillating regions42A and42B while the n-type electrode52B mainly serves as the common electrode to the laser oscillating regions42C and42D.

A method of fabricating the multi-beam semiconductor laser device40in accordance with the present embodiment will be explained with respect toFIG. 3Ato FIG.3D and FIG.4A and FIG.4B.

First, as illustrated inFIG. 3A, the GaN seed crystal layer56is grown on the C-plane of the sapphire substrate44by MOCVD (Metal Organic Chemical Vapor Deposition). When the GaN seed crystal layer56is grown on the sapphire substrate44sandwiching a GaN buffer layer (not shown in the figure), the GaN buffer layer is grown on the sapphire substrate44at a low temperature by MOCVD followed by growing the GaN seed crystal layer56on the GaN buffer layer.

At this time, after displacing the substrate from an MOCVD apparatus, a protective mask57is formed on the GaN seed crystal layer56in the form of a predetermined stripe extending in a predetermined direction as illustrated in FIG.3B.

Next, as illustrated inFIG. 3C, the GaN seed crystal layer56is etched with the protective mask57followed by removing the protective mask57. By this step, as illustrated inFIG. 3D, the concavo-convex structure of the GaN seed crystal layer56is formed on the sapphire substrate44.

The substrate is placed again in the MOCVD apparatus in which the n-type GaN contact layer54is formed as illustrated inFIG. 4Aon the GaN seed crystal layer56as the convex portion of the concavo-convex structure under a growth condition enabling a quick crystal growth in the lateral direction. Next, an n-type AlGaN cladding layer58, an n-type GaN light guide layer60, an active layer62, a p-type GaN light guide layer64, a p-type AlGaN cladding layer66and a p-type GaN contact layer68are sequentially laminated thereon. Next, the laser oscillating region42A to42D are formed by etching the p-type GaN contact layer68and the upper portions of the p-type AlGaN cladding layer66as illustrated in FIG.4B. However, only the laser oscillating regions42A and42B are illustrated in FIG.4B.

Next, although not shown in the figure, the mesa structure46is formed by etching the lower portion of the p-type AlGaN cladding layer66, the p-type GaN light guide layer64, the active layer62, the n-type GaN light guide layer60, the n-type AlGaN cladding layer58and the upper portion of the n-type GaN contact layer54on the both sides of the laser oscillating regions42A and42D.

Next, after forming and then selectively removing the SiO2film70to form openings therein, the p-type common electrode48is formed thereon in order to make contact with the p-type GaN contact layers68of the respective laser oscillating regions42A to42D as well as the n-type common electrodes52A and52B on the n-type GaN contact layer54shared by the laser oscillating regions42A to42D.

Finally, the wafer (substrate) is diced into bars by cleavage along the plane perpendicular to the laser oscillating regions42A to42D, followed by dicing the bars in parallel to the laser oscillating regions42A to42D in order to fabricate the multi-beam semiconductor laser device40as illustrated in FIG.1. As explained in the above, in accordance with the present embodiment, the distance A between the laser oscillating region42A and the laser oscillating region42D, the distance between the n-type electrode52A and the laser oscillating region42D and the distance between the n-type electrode52B and the laser oscillating region42A are designed in order to falls within a predetermined range and therefore it is possible to increase and make equal the optical output levels of the respective laser oscillating regions42A to42D. Also, since the p-type electrode48and the n-type electrodes52A and52B are used as common electrodes, it is easy to adjust the alignment when mounting on a sub mount.

Second Embodiment of the First Invention

The present embodiment is related to another example of a multi-beam semiconductor laser device in accordance with the first invention.FIG. 5is a schematic cross section view showing the overall configuration of the multi-beam semiconductor laser device. InFIG. 5, like references indicate similar elements as illustrated in FIG.1andFIG. 2, and therefore redundant explanation is not repeated.

The multi-beam semiconductor laser device72in accordance with the present embodiment is a GaN base multi-beam semiconductor laser device provided with four laser oscillating regions42A to42D as illustrated inFIG. 5which are capable of emitting laser beams with the same wavelength.

The laser oscillating regions42A to42D are provided with a p-type common electrode48on a mesa structure46which is formed on a sapphire substrate44, and have active regions50A to50D respectively. Also, one n-type electrode74are provided on an n-type GaN contact layers54and located as a common electrode opposite to the p-type common electrode48of the respective laser oscillating regions42A to42D on one side of a mesa structure46.

In the case of the present embodiment, the intervals between adjacent ones of the laser oscillating regions42A to42D are equal to each other. Also, the width W of the mesa structure46in the direction parallel to the sapphire substrate44is 200 μm to 300 μm while the distance A between the laser oscillating region42A and the laser oscillating region42D is 48 μm. The distance B between the laser oscillating region42D and the edge of the n-type electrode74just adjacent to the laser oscillating region is 108 μm while the distance between the laser oscillating region42A and the edge of the n-type electrode74just adjacent to the laser oscillating region is 60 μm. The configuration of the respective laser oscillating regions42A to42D and the laminate structure under these areas are designed corresponding to those of the multi-beam semiconductor laser device40in accordance with the first embodiment of the first invention.

Also, in the case of the multi-beam semiconductor laser device72in accordance with the present embodiment, there are the same advantages as in the case of the multi-beam semiconductor laser device40in accordance with the first embodiment of the first invention.

Third Embodiment of the First Invention

The present embodiment is related to a further example of a multi-beam semiconductor laser device in accordance with the first invention.FIG. 6is a schematic cross section view showing the overall configuration of the multi-beam semiconductor laser device. InFIG. 6, like references indicate similar elements as illustrated in FIG.1andFIG. 2, and therefore redundant explanation is not repeated.

The multi-beam semiconductor laser device76in accordance with the present embodiment is a GaN base multi-beam semiconductor laser device provided with four laser oscillating regions42A to42D as illustrated inFIG. 6which are capable of emitting laser beams with the same wavelength.

The laser oscillating regions42A and42B are provided with a p-type common electrode48A on a mesa structure46A which is formed on a sapphire substrate44, and have active regions50A and50B respectively. The laser oscillating regions42C and42D are provided with a p-type common electrode48B on a mesa structure46B which is formed on a sapphire substrate44, and have active regions50C and50D respectively.

Also, one n-type electrode78are provided on an n-type GaN contact layers54between the mesa structure46A and the mesa structure46B and located as a common electrode opposite to the p-type common electrode48A of the respective laser oscillating regions42A and42B and opposite to the p-type common electrode48B of the laser oscillating regions42C and42D. The mesa structure46A and the laser oscillating regions42A and42B, and the mesa structure46B and the laser stripes42C and42D are symmetrically provided with the n-type electrode78as the center of inversion.

The widths W of the mesa structures46A and46B in the direction parallel to the substrate are 150 μm to 250 μm respectively while the distance A1between the laser oscillating region42A and the laser oscillating region42B and the distance A2between the laser oscillating region42C and the laser oscillating region42D are 16 μm respectively.

The distance B1between the laser oscillating region42A and the n-type electrode78and the distance B2between the laser oscillating region42D and the n-type electrode78are 76 μm respectively while the distance between the laser oscillating region42B and the n-type electrode78and the distance between the laser oscillating region42C and the edge of the n-type electrode78are 60 μm respectively The configuration of the respective laser oscillating regions42A to42D and the laminate structures under these areas are designed corresponding to those of the multi-beam semiconductor laser device40in accordance with the first embodiment of the first invention.

Also, in the case of the multi-beam semiconductor laser device76in accordance with the present embodiment, there are the same advantages as in the case of the multi-beam semiconductor laser device40in accordance with the first embodiment of the first invention.

Fourth Embodiment of the First Invention

The present embodiment is related to a further example of a multi-beam semiconductor laser device in accordance with the first invention.FIG. 7is a schematic cross section view showing the overall configuration of the multi-beam semiconductor laser device. InFIG. 7, like references indicate similar elements as illustrated in FIG.1andFIG. 2, and therefore redundant explanation is not repeated.

The multi-beam semiconductor laser device80in accordance with the present embodiment is a multi-beam semiconductor laser array composed of multi-beam semiconductor laser devices72arranged in parallel on a common substrate82as illustrated inFIG. 7(for the sake of clarity in explanation, only three multi-beam semiconductor laser device72A,72B and72C are illustrated inFIG. 7while the multi-beam semiconductor laser devices72A and72B are partially illustrated). Each multi-beam semiconductor laser device is provided with four laser oscillating regions42A to42D which are capable of emitting laser beams with the same wavelength.

The n-type electrode74A formed on the common n-type GaN contact layer84located between the multi-beam semiconductor laser device72A and the multi-beam semiconductor laser device72B serves as the n-type common electrode of the multi-beam semiconductor laser device72A and the multi-beam semiconductor laser device72B, particularly as the n-type common electrode of the laser oscillating regions42A and42B of the multi-beam semiconductor laser device72A and the laser oscillating regions42C and42D of the multi-beam semiconductor laser device72B.

In the same way, the n-type electrode74B formed on the common n-type GaN contact layer84located between the multi-beam semiconductor laser device72B and the multi-beam semiconductor laser device72C serves as the n-type common electrode of the multi-beam semiconductor laser device72B and the multi-beam semiconductor laser device72C, particularly, serves as the n-type common electrode of the laser oscillating regions42A and42B of the multi-beam semiconductor laser device72B and the laser oscillating regions42C and42D of the multi-beam semiconductor laser device72C.

Each of the multi-beam semiconductor laser devices40,72,76and80in accordance with the first to fourth embodiments of the first invention is mounted, in a junction down fashion, on a sub mount which is provided with first junction electrodes to be electrically connected to the n-type electrode and second junction electrodes to be electrically connected to the p side electrode.

For example, the multi-beam semiconductor laser device80in accordance with the fourth embodiment of the first invention is mounted, in a junction down fashion, on a sub mount90which is provided with first junction electrodes92A and92B to be electrically connected to the n-type electrode74A and74B and second junction electrodes94A,94B and94C to be electrically connected to the p side electrode48as illustrated in FIG.8.

The sub mount90is a member in the form of a plate made of AlN. The first junction electrodes92A and92B is formed on the sub mount90as illustrated in FIG.8and made of dual layered metallic film comprising a Ti/Pt/Au layer92awhich is formed by laminating titanium, platinum and gold on the sub mount90in this order and has a large film thickness, and a Ti/Ag/Sn layer92bwhich is formed by laminating titanium, silver (Ag) and tin (Sn) in this order and has a small film thickness. The film thickness of Ti/Pt/Au layer92ais adjusted in order that the height of the first junction electrode is larger than that of the second junction electrodes94A to94C corresponding to the differential height between the p-type common electrode48and the n-type electrodes74A and74B of the multi-beam semiconductor laser device.

The second junction electrodes94A to94C are formed on the sub mount90and comprises a dual layered metallic film formed on the sub mount90and composed of a Ti/Pt/Au layer94awhich is laminated on the sub mount90and a Ti/Ag/Sn layer94bwhich is laminated on the Ti/Pt/Au layer94awith the substantially same film thickness as illustrated in FIG.8.

Also, as illustrated inFIG. 9, the first junction electrode92is formed from the Ti/Pt/Au layer92ahaving a small film thickness and the Ti/Ag/Sn layer92bhaving a large film thickness. The film thickness of Ti/Ag/Sn layer92bis adjusted in order that the height of the first junction electrode is larger than that of the second junction electrodes94A to94C corresponding to the differential height between the p-type common electrode48and the n-type electrodes74A and74B of the multi-beam semiconductor laser device.

Embodiment of the Second Invention

The present embodiment is related to an example of a multi-beam semiconductor laser device in accordance with the second invention.FIG. 12is a cross section view showing the location of the seed crystal area and the meeting location in relation to the location of a laser oscillating region as well as the configuration of the laser oscillating region in accordance with the present embodiment.

The laser oscillating region110of the multi-beam semiconductor laser device in accordance with the present embodiment is a ridge-type laser oscillating region in which current is confined by an SiO2film132as illustrated in FIG.12.

An n-type GaN contact layer116is provided on the C-plane of the sapphire substrate112by a lateral growth process from GaN seed crystal members114A and114B which are periodically formed. Meanwhile, although not shown in the figure, a GaN buffer layer may be formed between the sapphire substrate112and the GaN seed crystal members114A and114B by a growth process at a low temperature. A laminate structure is formed on the n-type GaN contact layer116by sequentially laminating an n-type AlGaN cladding layer118, an n-type GaN light guide layer120, an active layer122, a p-type GaN light guide layer124, a p-type AlGaN cladding layer126and a p-type GaN contact layer128. The regions located above the GaN seed crystal members114A and114B are high density defective regions. Furthermore, located midway between the GaN seed crystal member114A and the GaN seed crystal member114B is a meeting location130which is another high density defective region.

The upper portion of the p-type AlGaN cladding layer126and the p-type GaN contact layer128comprise the laser oscillating region110, and are extending in one direction in the form of a ridge stripe as located in the low density defective region between the GaN seed crystal member114A and the meeting location130.

The laser oscillating region110is coated with the SiO2film132and provided with a p-type electrode134on the p-type GaN contact layer128through an opening of the SiO2film132.

Also, not shown in the figure, an n-type electrode is formed on the n-type GaN contact layer116adjacent to a mesa structure on top of which the laser oscillating region110is located.

In the case where the width of the laser oscillating region110is W, where the distance between the laser oscillating region110and the GaN seed crystal member114A is X1, and where the distance between the laser oscillating region110and the meeting location130is X2, then W is for example 1.6 μm, X1satisfies X1≧0.5 μm for example 2 μm, and X2satisfies X2≧0.5 μm for example 2 μm.

As explained in the above, in accordance with the present embodiment, since the laser oscillating region110is formed on the low density defective region between the GaN seed crystal member114A and the meeting location130, it is possible to obtain good laser characteristics and a long device life cycle.

Also, it is possible to realize a semiconductor laser device capable of emitting beams at a high output power level by implementing a plurality of the laser oscillating regions110in accordance with the present embodiment in a multi-beam semiconductor laser device.

Embodiment of the Third Invention

The present embodiment is related to an example of a multi-beam semiconductor laser device in accordance with the third invention.FIG. 13is a cross section view showing the location of the seed crystal area and the meeting location in relation to the location of a laser oscillating region as well as the configuration of the laser oscillating region in accordance with the present embodiment. InFIG. 13, like references indicate similar elements as illustrated inFIG. 12, and therefore redundant explanation is not repeated.

The laser oscillating regions140A,140B and140C of the multi-beam semiconductor laser device in accordance with the present embodiment are located on low density defective regions respectively, each adjacent ones of the low density defective regions being located with the GaN seed crystal member114or the meeting location130inbetween.

Namely, the laser oscillating region140A and the laser oscillating region140B are located in the low density defective regions adjacent to each other with the GaN seed crystal member114A inbetween. Also, the laser oscillating region140B and the laser oscillating region140C are located in the low density defective regions adjacent to each other with the meeting location130inbetween.

The laser oscillating region140B has the same spatial relationship to the GaN seed crystal member114A and the meeting location130as in the embodiment of the second invention. In the case where the width of the laser oscillating region140B is W, where the distance between the GaN seed crystal member114A and the laser oscillating region140B is X1, and where the distance between the laser oscillating region140B and the meeting location130is X2, then W is for example 1.6 μm, X1satisfies X1≧0.5 μm for example 2 μm, and X2satisfies X2≧0.5 μm for example 2 μm.

On the other hand, the laser oscillating region140A and the laser oscillating region140C has the same width as the laser oscillating region140B.

In the case where the distance between the laser oscillating region140A and the GaN seed crystal member114A is X3and where the distance between the meeting location130and the laser oscillating region140C is X4, then X3satisfies X3≧0.5 μm for example 2 μm, and X4satisfies X4≧0.5 μm for example 2 μm.

As explained in the above, in accordance with the present embodiment, since the laser oscillating regions140A to140C are formed on the low density defective regions between the GaN seed crystal members and the meeting locations, it is possible to obtain good laser characteristics and a long device life cycle.

Also, it is possible to realize a semiconductor laser device capable of emitting beams at a high output power level by implementing a plurality of the laser oscillating regions140A to140C in accordance with the present embodiment in a multi-beam semiconductor laser device.

Embodiment of the Fourth Invention

The present embodiment is related to an example of a multi-beam semiconductor laser device in accordance with the fourth invention.FIG. 14is a cross section view showing the location of the seed crystal area and the meeting location in relation to the location of a laser oscillating region as well as the configuration of the laser oscillating region in accordance with the present embodiment. InFIG. 14, like references indicate similar elements as illustrated inFIG. 12, and therefore redundant explanation is not repeated.

The laser oscillating regions150A,150B,150C and150D of the multi-beam semiconductor laser device in accordance with the present embodiment are located on low density defective regions respectively, each adjacent ones of the low density defective regions being located with the GaN seed crystal member114A or114B or the meeting location130inbetween. In this case, two of the laser oscillating regions are located on each low density defective region.

Namely, the laser oscillating regions150A and150B are located on the low density defective region between the GaN seed crystal member114A and the meeting location130. Also, the laser oscillating regions150C and150D are located on the low density defective region between the meeting location130and the GaN seed crystal member114B.

The laser oscillating regions150A to150D have the same width W, for example, 1.6 μm.

In the case where the distance between the GaN seed crystal member114A and the laser oscillating region150A is X1, where the distance between the laser oscillating region150B and the meeting location130is X2, where the distance between the meeting location130and the laser oscillating region150C is X3, and where the distance between the laser oscillating region150D and the GaN seed crystal member114B is X4, then X1, X2, X3and X4are no smaller than 0.5 μm respectively, for example, 2 μm, 2 μm, 2 μm and 2 μm,

As explained in the above, in accordance with the present embodiment, since the laser oscillating regions150A to150D are formed on the low density defective regions between the GaN seed crystal members and the meeting locations, it is possible to obtain good laser characteristics and a long device life cycle.

Also, it is possible to realize a semiconductor laser device capable of emitting beams at a high output power level by implementing a plurality of the laser oscillating regions150A to150D in accordance with the present embodiment in a multi-beam semiconductor laser device.

Embodiment of the Fifth Invention

The present embodiment is related to an example of a multi-beam semiconductor laser device in accordance with the fifth invention.FIG. 15is a cross section view showing the location of the seed crystal area and the meeting location in relation to the location of a laser oscillating region as well as the configuration of the laser oscillating region in accordance with the present embodiment. InFIG. 15, like references indicate similar elements as illustrated inFIG. 12, and therefore redundant explanation is not repeated.

The laser oscillating regions160A,160B and160C of the multi-beam semiconductor laser device in accordance with the present embodiment are located on every other low density defective region respectively as illustrated in FIG.15.

Namely, the laser oscillating regions160A to160C are located respectively on the low density defective region between the GaN seed crystal member114A and the meeting location130A, on the low density defective region between the GaN seed crystal member114B and the meeting location130B, and on the low density defective region between the GaN seed crystal member114C and the meeting location130C.

On the other hand, there is provided no laser oscillating region on the low density defective region between the meeting location130A and the GaN seed crystal member114B, on the low density defective region between the meeting location130B and the GaN seed crystal member114C and on the low density defective region between the meeting location130C and the GaN seed crystal member114D.

The GaN seed crystal members114A to114C, as well as the meeting locations180A to130C, are periodically formed on the sapphire substrate112.

The laser oscillating regions160A to160C have the same width W, for example, 1.6 μm.

In the case where the distance between the GaN seed crystal member114A and the laser oscillating region160A is X1, where the distance between the laser oscillating region160A and the meeting location130A is X2, where the distance between the GaN seed crystal member114B and the laser oscillating region160B is X3, where the distance between the laser oscillating region160B the meeting location130B is X4, where the distance between the laser oscillating region160C and the meeting location114C is X5and where the distance between the laser oscillating region160C and the meeting location130C is X6, then X1, X2, X3, X4, X5and X6are no smaller than 0.5 μm respectively, for example, 2 μm, 2 μm, 2 μm, 2 μm, 2 μm and 2 μm,

As explained in the above, in accordance with the present embodiment, since the laser oscillating regions160A to160C are formed on the low density defective regions, it is possible to obtain good laser characteristics and a long device life cycle.

Also, it is possible to realize a semiconductor laser device capable of emitting beams at a high output power level by implementing a plurality of the laser oscillating regions160A to160C in accordance with the present embodiment in a multi-beam semiconductor laser device.

Although only one laser oscillating region is located on one low density defective region between the GaN seed crystal member114and the meeting location130in accordance with the embodiment of the second invention, the embodiment of the third invention and the embodiment of the fifth invention, it is possible to arrange in one low density defective region a plurality of the laser oscillating region.

First Embodiment of the Sixth Invention

The present embodiment is related to an example of a multi-beam semiconductor laser device in accordance with the sixth invention.FIG. 19is a cross section view showing the configuration of a GaN base multi-beam semiconductor laser device.

The multi-beam semiconductor laser device210in accordance with the present embodiment is a GaN base multi-beam semiconductor laser device provided with four laser oscillating regions212A,212B,212C and212D as illustrated inFIG. 19which are capable of emitting laser beams with the same wavelength.

The laser oscillating regions212A to212D are fabricated on a common mesa structure216, which is formed on a sapphire substrate214, and provided with the active region220A,220B,220C and220D respectively. A p-type common electrode218is formed on the respective laser oscillating regions212A to212D and includes stripe electrodes of the respective laser oscillating regions212A to212D while the active regions220A,220B,220C and220D are located under the p-type common electrode218. In this case, each stripe electrode is a portion of the p-type common electrode218corresponding to one of the respective laser oscillating regions212A to212D. Meanwhile, the area of the stripe electrode corresponding to each of the respective laser oscillating regions212A to212D is restricted by an SiO2film226as will be explained infra with reference to FIG.20.

Also, two n-type electrodes222A and222B are provided on an n-type GaN contact layer224and located as common electrodes opposite to the p-type common electrode218on both sides of the mesa structure216.

The distance l(a-c) between the center of the laser oscillating region212C and the edge of the n-type electrode222A just adjacent to the laser oscillating region is 250 μm while the distance l(b-c) between the center of the laser oscillating region212C and the edge of the n-type electrode222B just adjacent to the laser oscillating region is 70 μm.

Also, the distance l(b-d) between the center of the laser oscillating region212D and the edge of the n-type electrode222B just adjacent to the laser oscillating region is 60 μm while the distance l(a-d) between the center of the laser oscillating region212D and the edge of the n-type electrode222A just adjacent to the laser oscillating region is 260 μm.

The relationships of the laser oscillating regions212A and212B and the n-type electrodes222A and222B in regard to the respective distances therebetween are the same as the relationships of the laser oscillating regions212C and212D and the n-type electrodes222A and222B in regard to the respective distances therebetween.

In accordance with the present embodiment, the interval between the laser oscillating region212B and the laser oscillating region212C is larger than the interval between the laser oscillating region212A and the laser oscillating region212B and larger than the laser oscillating region212C and the laser oscillating region212D. This is only for the purpose of facilitating the test procedure of the multi-beam semiconductor laser device210while it is not requisite to make relatively wider the interval between the laser oscillating region212B and the laser oscillating region212C but it is possible to make the interval equal to the interval between the other laser oscillating regions.

Each of the laser oscillating regions212A to212D is an air-ridge type laser oscillating region in which current is confined by an SiO2film226as illustrated inFIG. 20, like the multi-beam semiconductor laser device40in accordance with the first embodiment of the first invention.

A GaN seed crystal layer228, an n-type GaN contact layer224, an n-type AlGaN cladding layer230, an n-type GaN light guide layer232, an active layer234, a p-type GaN light guide layer236, a p-type AlGaN cladding layer238and a p-type GaN contact layer240are sequentially laminated on the C-plane of the sapphire substrate214in a laminate structure. Meanwhile, not shown in the figure, a GaN buffer layer may be grown at a low temperature between the sapphire substrate214and the GaN seed crystal layer228.

The upper portion of the p-type AlGaN cladding layer238and the p-type GaN contact layer240are functioning as the laser oscillating region212A and extending in the form of a ridge stripe in one direction.

Also, the upper portion of the n-type GaN contact layer224and the n-type AlGaN cladding layer230, the n-type GaN light guide layer232, the active layer234, the p-type GaN light guide layer236and the lower portion of the p-type AlGaN cladding layer238are formed as the mesa structure216extending in the same direction as the laser oscillating region212A is extending.

Meanwhile, the mesa structure216is formed as a common mesa structure of the laser oscillating region212A to212D. In other words, the n-type GaN contact layer224, the n-type AlGaN cladding layer230, the n-type GaN light guide layer232, the active layer234, the p-type GaN light guide layer236and the p-type AlGaN cladding layer238are formed as a common laminate structure to the respective laser oscillating region212A to212D.

Furthermore, the GaN seed crystal layer228is formed as a concavo-convex structure extending in the same direction as the laser oscillating region212A and the mesa structure216are extending while the laser oscillating region212A is located between two concave portions of the concavo-convex structure.

The laser oscillating region212A to212D, the mesa structure216and the n-type GaN contact layer224adjacent to the mesa structure216are coated with the SiO2film226except for the upper surface of the laser oscillating region212A to212D and the openings provided part of the n-type GaN contact layer224.

The p-type common electrode218made of a multi-layered metallic film such as a Pd/Pt/Au electrode is formed over the respective p-type GaN contact layer240, as a common ohmic junction electrode to the respective laser oscillating region212A to212D through openings of the SiO2film226.

Also, n-type electrodes222A and222B made of a multi-layered metallic film such as Ti/Al/Pt/Au electrodes are formed on the n-type GaN contact layer224on both sides of the mesa structure216, as common ohmic junction electrodes to the respective laser oscillating region212A to212D through openings of the SiO2film226.

However, because of the respective distances between the laser oscillating regions212A to212D and the n-type electrodes222A and222B, the n-type electrode222A mainly serves as the common electrode to the laser oscillating regions212A and212B while the n-type electrode222B mainly serves as the common electrode to the laser oscillating regions212C and212D.

In the case of the multi-beam semiconductor laser device210in accordance with the present embodiment as operated at 30 mW or thereabout, ρv·d/L is 30 Ωμm and rsh/L is 150 Ωμm. However, ρv is the effective specific resistance in the longitudinal direction from the p-type common electrode218through the active layer234; d is the effective thickness in the longitudinal direction from the p-type common electrode218to the active layer234through the active layer234, i.e., the thickness of the mesa structure216; rsh is the sheet resistance from the p-type common electrode218to the n-type electrodes222A and222B; and L is the resonator length.

The outer laser oscillating region212D is the first oscillating area (1) from the common n-type electrode222B while the inner laser oscillating region212C is the second laser oscillating region (2) from the common n-type electrode222B.

Uniform current injection becomes possible in accordance with the above described equation 2 if the area S(1) of the stripe electrode of the laser oscillating region (1) and the area S(2) of the stripe electrode of the laser oscillating region (2) satisfy
(ρv·d)/(S(1))+A1=(ρv·d)/(S(2))+A2
A1=rsh·(lN(1)·1F(1))/(lN(1)+1F(1))·1/L
A2=rsh·(lN(2)·1F(2))/(lN(2)+1F(2))·1/L
where lN(1) is the distance in the lateral direction between the laser oscillating region (1) and the common electrode near to the laser oscillating region (1), i.e., the n-type electrode222B; 1F(1) is the distance in the lateral direction between the laser oscillating region (1) and the common electrode remote from the laser oscillating region (1), i.e., the n-type electrode222A, lN(2) is the distance in the lateral direction between the laser oscillating region (2) and the common electrode near to the laser oscillating region (2), i.e., the n-type electrode222B, 1F(2) is the distance in the lateral direction between the laser oscillating region (2) and the common electrode remote from the laser oscillating region (2), i.e., the n-type electrode222A, and L is the resonator length.

Also, in the case where the respective widths of the laser oscillating region (1) and the laser oscillating region (2), more exactly speaking, the widths of the stripe electrodes (the width W as illustrated inFIG. 20) are W(1) and W(2), then
S(1)=W(1)·L
S(2)=W(2)·L

and therefore, when W(1) is set to be 1.5 μm in designing the p-type common electrode218, it is possible by setting W(2) to be 1.53 μm to make uniform the luminescence intensities of the respective laser oscillating regions212A to212D as illustrated in FIG.21. Meanwhile, the widths of the laser oscillating regions212A and212B are the same as the widths of the laser oscillating regions212C and212D respectively.

Second Embodiment of the Sixth Invention

The present embodiment is related to another example of a multi-beam semiconductor laser device in accordance with the sixth invention.FIG. 22is a schematic cross section view showing the configuration of the multi-beam semiconductor laser device. InFIG. 22, like references indicate similar elements as illustrated in FIG.19andFIG. 20, and therefore redundant explanation is not repeated.

The multi-beam semiconductor laser device in accordance with the present embodiment is provided with two laser oscillating region212C and212D on the common mesa structure216as illustrated in FIG.22and has the same configuration as the multi-beam semiconductor laser device210in accordance with the first embodiment of the sixth invention except that one common n-type electrode222is located aside of the laser oscillating region212D.

Namely, the distance l(1) between the edge of the n-type electrode222just adjacent to the laser oscillating region and the center of the laser oscillating region212D (the first oscillating area (1) from the common n-type electrode222) is 60 μm while the distance l(2) between the edge of the n-type electrode222just adjacent to the laser oscillating region and the center of the laser oscillating region212C (the first oscillating area (2) from the common n-type electrode222) is 70 μm.

In the case where the multi-beam semiconductor laser device is operated at 30 mW or thereabout, ρv·d/L is 30 Ωμm and rsh/L is 150 Ωμm. It is possible to uniformly inject electric current in accordance with the above described equation 1 if satisfying
(ρv·d)/(W1·L)+B1=(ρv·d)/(W2·L)+B2
B1=rsh·l(1)·1/L
B2=rsh·l(2)·1/L
where W1 and W2 are the respective widths of the laser oscillating region (1) and the laser oscillating region (2), more exactly speaking, the widths of the stripe electrodes.

Accordingly, if W1 is set to be 1.5 μm when designing the p-type electrode, it is possible by setting W2 to be 1.55 μm to make uniform the luminescence intensities of the respective laser oscillating regions212C and212D.

Third Embodiment of the Sixth Invention

The present embodiment is related to a further example of a multi-beam semiconductor laser device in accordance with the sixth invention.FIG. 23is a plan view showing the configuration of the multi-beam semiconductor laser device in accordance with the present embodiment. InFIG. 23, like references indicate similar elements as illustrated in FIG.19andFIG. 20, and therefore redundant explanation is not repeated.

The multi-beam semiconductor laser device in accordance with the present embodiment has the same configuration as the multi-beam semiconductor laser device210in accordance with the first embodiment of the sixth invention except that the laser oscillating regions212B and212C are tapered laser oscillating regions.

In the case of the present embodiment, as illustrated inFIG. 23, while the resonator length L is 600 μm, the laser oscillating regions212B and212C includes center portions whose stripe width Wc is constant at 1.66 μM and side portions which are extending from the center portions and become narrower toward the light emitting end surfaces where the stripe width We is 1.5 μm. The laser oscillating regions212B and212C are tapered by making broken lines the edges of the side portions near the laser oscillating region212A and the laser oscillating region212D.

The lengths Lc of the center portions are 400 μm while the lengths Le of the side portions as tapered are 100 μm.

The distance lN(1) between the center of the laser oscillating region212D (the laser oscillating region (1)) and the edge of the n-type electrode222B just adjacent to the laser oscillating region is 60 μm while the distance lF(1) between the center of the laser oscillating region212D and the edge of the n-type electrode222A just adjacent to the laser oscillating region is 260 μm.

Also, the distance 1N(2) between the center of the laser oscillating region212C (the laser oscillating region (2)) and the edge of the n-type electrode222B just adjacent to the laser oscillating region is 70 μM while the distance lF(2) between the center of the laser oscillating region212C and the edge of the n-type electrode222A just adjacent to the laser oscillating region is 250 μm.

In the case where the multi-beam semiconductor laser device is operated at 30 mW or thereabout, ρv·d/L is 30 Ωμm and rsh/L is 150 Ωμm. Uniform current injection becomes possible in accordance with the above described equation 2 if satisfying
(ρv·d)/S(1)+A1=(ρv·d)/S(2)+A2
A1=rsh·(lN(1)·1F(1))/(lN(1)+1F(1))·1/L
A2=rsh·(lN(2)·1F(2))/(lN(2)+1F(2))·1/L
where S(1) and S(2) are the area of the laser oscillating region212D near to the n-type electrode222B and the area of the laser oscillating region212C remote from the n-type electrode222B.

Accordingly, if S(1) is set to be 900 μm2when designing the p-type electrode, it is possible by setting S(2) to be 916 μm2to make uniform the luminescence intensities of the respective laser oscillating regions212A to212D. Meanwhile, the stripe areas of the laser oscillating regions212A and212B are the same as the areas of the laser oscillating regions212C and212D respectively.

The multi-beam semiconductor laser device in accordance with the first invention has a common substrate provided with a mesa structure on which a plurality of laser oscillating regions are fabricated in the form of stripes, and comprises: a first electrode provided for each of the plurality of laser oscillating regions for functioning as one of a p-type electrode and an n-type electrode of each laser oscillating region; and a second electrode located aside of the mesa structure on the common substrate as a common electrode to at least two of the plurality of the laser oscillating regions for functioning as the other of the p-type electrode and the n-type electrode of each of the two laser oscillating regions and as an opposite electrode to the first electrode, and therefore it is easy to adjust the alignment of electrodes when mounting on a sub mount, and particularly the invention is suitably applied to GaN base devices.

Also, the equations of A≦100 μm and B≦150 μm are satisfied where A is a distance between one of the laser oscillating regions closest to an edge of the common electrode aside of the laser oscillating regions and another of the laser oscillating regions farthest from the edge of the common electrode; and B is a distance between another of the oscillating regions farthest from the edge of the common electrode and the edge of the common electrode aside of the laser oscillating regions, and therefore it is possible to increase and make equal the optical output levels of the respective laser oscillating regions.

Furthermore, in the case of the multi-beam semiconductor laser devices in accordance with the second to fifth inventions, the equations of X1≧0.5 μm and X2≧0.5 μm are satisfied where X1is a distance between each of the laser oscillating regions and one of the seed crystal areas, and X2is a distance between each of the laser oscillating regions and one of the meeting locations, and therefore it is possible to arrange a plurality of laser oscillating regions in low density defective regions. By this configuration, a high reliability semiconductor laser device having good laser characteristics, a high optical output level and a long device life cycle can be realized.

Furthermore, the multi-beam semiconductor laser device in accordance with the sixth invention comprises a first electrode comprising stripe electrodes provided for each of a plurality of laser oscillating regions for functioning as one of a p-type electrode and an n-type electrode of the laser oscillating region; and a second electrode located aside of the mesa structure on the common substrate as a common electrode to at least two of the plurality of the laser oscillating regions for functioning as the other of the p-type electrode and the n-type electrode of each of the two laser oscillating regions and as an opposite electrode to the first electrode, wherein the plurality of the stripe electrodes of the first electrode have different areas corresponding to the distances thereof from the common electrode in order to flow a substantially same current from the stripe electrodes of the first electrode, and therefore it is possible to make uniform the luminescence intensities of the respective laser oscillating regions. Accordingly, it is possible to make uniform the degradation of the active regions of the respective laser oscillating regions and to significantly improve the device life cycle as compared with that of a multi-beam semiconductor laser device emitting laser beams at dispersed luminescence intensities. Also, since there is no dispersion in the luminescence intensities of the respective laser oscillating regions, it is possible to expand the range of applications of the multi-beam semiconductor laser.

It is obvious that various implementations and modifications of the present invention are possible with reference to the explanation as described above. Accordingly, it is possible to implement the present invention in other embodiments than those explained in the above detailed description within the scope as equivalently recited in the following claims.