Self-supported nitride semiconductor substrate and its production method, and light-emitting nitride semiconductor device using it

A self-supported nitride semiconductor substrate of 10 mm or more in diameter having an X-ray diffraction half width of 500 seconds or less in at least one of a {20-24} diffraction plane and a {11-24} diffraction plane.

FIELD OF THE INVENTION

The present invention relates to a self-supported nitride semiconductor substrate for use in light-emitting devices having large light emission with a low driving voltage, a method for producing such a self-supported nitride semiconductor substrate, and a light-emitting nitride semiconductor device formed by using such a self-supported nitride semiconductor substrate.

BACKGROUND OF THE INVENTION

Because the crystal growth of nitride semiconductors in a bulk form from its melt is generally difficult, a self-supported nitride semiconductor substrate is obtained by growing nitride semiconductor layer on a different base substrate such as sapphire and gallium arsenide, and removing layers ranging from the base substrate to leave the nitride semiconductor layer only.

The formation of a nitride semiconductor layer on a different base substrate of sapphire, etc. with large lattice mismatch is usually achieved not by the epitaxial growth of a nitride semiconductor coherent with the lattice of the base substrate, but by growing crystal nuclei in many points on the base substrate to such an extent that they are integrated to a continuous film. Accordingly, a film obtained by integrating such nitride semiconductor crystals does not have a lattice plane completely parallel to that of the substrate (not completely flat surface), resulting in slight deviations of crystal orientations therebetween. It is common to use a diffraction half width determined by an X-ray diffraction method as a method for evaluating crystal quality such as the deviations of crystal orientations, etc.

The quality of nitride semiconductor substrates is conventionally evaluated by a half width of an X-ray rocking curve in a {0002} or {0004} diffraction plane, and the smaller the half width, the higher the quality of the nitride semiconductor. For instance, Japanese patent 3,184,717 discloses a GaN single crystal as thick as 80 μm or more having a half-width of 5 to 250 seconds in a two-crystal X-ray rocking curve, which serves as a substrate, on which a GaN semiconductor crystal layer is grown. JP 10-053495 A discloses a nitride single crystal of 10 mm or more in both length and width and 300 μm or more in thickness, or 20 mm or more in length and 10 μm or more in diameter, which has a half width of 5 minutes or less in an X-ray diffraction rocking curve.

OBJECTS OF THE INVENTION

However, it has been found that even self-supported nitride semiconductor substrates having an X-ray diffraction half width in a {0002} symmetric diffraction plane are as small as, for instance, 250 seconds or less, some light-emitting devices such as LEDs formed thereon exhibit only low brightness. Namely, the conventional evaluation standards do not necessarily secure the formation of self-supported nitride semiconductor substrates for producing light-emitting devices capable of providing high emission power at low driving voltage.

Accordingly, an object of the present invention is to provide a self-supported nitride semiconductor substrate for producing light-emitting devices capable of providing high emission power at low driving voltage.

Another object of the present invention is to provide a method for producing such a self-supported nitride semiconductor substrate.

A further object of the present invention is to provide a light-emitting device using such a self-supported nitride semiconductor substrate.

SUMMARY OF THE INVENTION

As a result of intense research in view of the above objects, the inventor has paid attention to the fact that X-ray diffraction half widths of {20-24} and {11-24} diffraction planes are proper as an evaluation standard replacing the half width of X-ray rocking curves of {0002} and {0004} symmetric diffraction planes, finding that when any one of them is 500 seconds or less, it is possible to obtain a self-supported nitride semiconductor substrate for producing light-emitting devices capable of providing high emission power at low driving voltage. The present invention has been achieved based on this finding.

Thus, the self-supported nitride semiconductor substrate of the present invention has an X-ray diffraction half width of 500 seconds or less in at least one of a {20-24} diffraction plane and a {11-24} diffraction plane, and a diameter of 10 mm or more. In this self-supported nitride semiconductor substrate, the nitride semiconductor is preferably undoped, or n- or p-type, and preferably has a carrier density of 1×1020cm−3or less.

The method of the present invention for producing the above self-supported nitride semiconductor substrate comprises (1) forming a first nitride semiconductor layer having a dislocation density of 10n/cm2(0<n≦10) on a base substrate; (2) forming a mask layer made of another material than the nitride semiconductor on the first nitride semiconductor layer; (3) providing the mask layer with openings having an area of 10−ncm2or less, which penetrate the mask layer in a thickness direction, at a density of 10−2/cm2or less; (4) forming a second nitride semiconductor layer having a thickness of 50 μm or more on the mask layer; and (5) removing layers ranging from the base substrate to the mask layer. The openings of the mask layer preferably has a density of 10n−4/cm2or less.

The growing of the nitride semiconductor is preferably carried out by a sublimation method, a metal-organic vapor phase epitaxy method, a hydride vapor-phase epitaxy method, liquid-phase epitaxy method or a combination thereof. The base substrate may be made of a different material from that of the self-supported substrate.

In the production of the self-supported nitride semiconductor substrate, the first nitride semiconductor layer may be formed on the base substrate via a buffer layer.

The light-emitting nitride semiconductor device of the present invention comprises an epitaxial nitride layer with a light-emitting device structure formed on the above self-supported nitride semiconductor substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The self-supported nitride semiconductor substrate of the present invention has an X-ray diffraction half width of 500 seconds or less in at least one of a {20-24} diffraction plane and a {11-24} diffraction plane. The term “self-supported substrate” used herein means a substrate having such strength that is not only enough to maintain its shape but also suitable for handling. To have such strength, the self-supported substrate may have a thickness of 50 μm, preferably 200 μm or more. To make the cleavage easy after the formation of devices, the self-supported substrate preferably has a thickness of 1 mm or less. When the self-supported substrate is too thick, the cleavage is difficult, resulting in a rough cleavage surface. If the self-supported substrate with a rough cleavage surface were used to produce semiconductor lasers, etc., they would have deteriorated characteristics due to reflection loss.

The nitride semiconductor in the self-supported nitride semiconductor substrate of the present invention may be grown by various methods such as a sublimation method, a metal-organic vapor phase epitaxy (MOVPE) method, a hydride vapor-phase epitaxy (HVPE) method, a liquid-phase epitaxy method, an epitaxial lateral overgrowth (ELO) method, or a combination thereof, and the ELO method is particularly preferable. In the ELO method, as shown inFIG. 1, a first nitride semiconductor layer2and a mask layer3are formed on a base substrate1in this order, and after providing the mask layer3with pluralities of openings31of desired size penetrating the mask layer3in a thickness direction, a second nitride semiconductor layer4is formed on the mask layer3. Finally, the base substrate1, the first nitride semiconductor layer2and the mask layer3are removed. Each step will be explained in detail below.

Materials usable for the base substrate1for growing the nitride semiconductor layers2,4are sapphire, silicon carbide, silicon, gallium arsenide, etc. However, the base substrate1made of these materials does not have good matching in a lattice constant with the nitride semiconductors2,4. Accordingly, it is preferable to form a buffer layer10on the base substrate1, and then epitaxially grow the nitride semiconductor layers2,4on the buffer layer. The buffer layer10may be a layer of GaN or AlN formed at about 500° C.

It is preferable that the first nitride semiconductor layer2formed on the buffer layer10is undoped with impurities, or n- or p-type, and has a carrier density of 1×1020cm−3or less. When the carrier density exceeds 1×1020cm−3, the concentration of n- or p-type impurities becomes too high, resulting in the deteriorated quality of the nitride semiconductor crystal.

The first nitride semiconductor layer2may be the same as the second nitride semiconductor layer4, which is used as a self-supported nitride semiconductor substrate. These nitride semiconductor layers2,4may be formed by a sublimation method, a metal-organic vapor phase epitaxy method, a hydride vapor-phase epitaxy method, a liquid-phase epitaxy method or a combination thereof. The first nitride semiconductor layer2preferably has a thickness of about 0.1 to 500 μm. The dislocation density of the first nitride semiconductor layer2is represented by 10nper cm2(0<n≦10), for the convenience of explanation.

The mask layer3formed on the first nitride semiconductor layer2is preferably made of materials such as high-melting point metals bearable at the growth temperature of a nitride semiconductor, or those having low wettability to the nitride semiconductor, such as SiN, TiN, SiO2, etc. The growth of a nitride semiconductor on the low-wettability mask layer3makes it possible to suppress the generation of crystal nuclei in other areas than the openings31in a thickness direction, thereby minimizing the deviation of crystal orientation, which would occur when crystal nuclei merge.

Though not particularly restrictive, the mask layer3is effectively provided with openings31by photolithography or selective etching, etc. The shapes of the openings31are not restrictive. Each opening31preferably has an area corresponding to a reciprocal (10−ncm2) of the dislocation density of an underlying crystal layer (first nitride semiconductor layer2) or less, more preferably 10−n−2cm2or less. In a case where the first nitride semiconductor layer2has a high dislocation density (n is large), the number of dislocations penetrating through the openings31from the first nitride semiconductor layer2can be suppressed by narrowing the openings31. The lower limit of the area of the opening31is preferably about 10−10cm2, taking into consideration the growth speed of nitride semiconductor crystal nuclei, the deviation of crystal orientation, the difficulty of forming openings, etc.

The number (density) of the openings31formed per a unit area of the mask layer3corresponds to the density of nitride semiconductor crystal nuclei generating thereon. When the crystal nuclei grow and merge with each other to form a continuous film, a slight deviation of crystal orientation tends to generate defects such as new dislocation, etc. Accordingly, the density of the openings31is preferably as small as possible. Also, taking into consideration the resistance to failure of the mask layer3, etc., the total area of the openings31should be sufficiently smaller than the total area of the mask layer3. Accordingly, the density of the openings31is preferably 10n−2/cm2or less, more preferably 10n−4/cm2or less. It should be noted, however, that when the density of the openings31is too low, the merger of crystal nuclei growing through the openings31takes too much time, so that the second nitride semiconductor layer4needs too much thickness for obtaining a nitride semiconductor layer with a low dislocation density. Accordingly, the lower limit of the density of the openings31is preferably about 102of openings per cm2.

The thickness of the mask layer3having such a structure is preferably about 0.01 to 10 μm. When the thickness of the mask layer3is less than 0.01 μm, the ELO method fails to provide sufficient effects. On the other hand, when the mask layer3is thicker than 10 μm, it takes too much time to for nitride semiconductor crystal nuclei to pass through the openings31.

The second nitride semiconductor layer4grown on the mask layer3may have a different composition from that of the first nitride semiconductor layer2. The carrier density of the second nitride semiconductor layer4is preferably in a range of 1×1020cm−3or less. When the carrier density of the second nitride semiconductor layer4is more than 1×1020cm−3, the concentration of n- or p-impurities is too high, resulting in a self-supported nitride semiconductor substrate with deteriorated quality.

The second nitride semiconductor layer4may be formed by a sublimation method, a metal-organic vapor phase epitaxy method, a hydride vapor-phase epitaxy method, a liquid-phase epitaxy method, or a combination thereof. The second nitride semiconductor layer4is turned to a self-supported substrate by mirror-polishing after removing layers ranging from the base substrate1to the mask layer3(for instance, the base substrate1, the buffer layer10, the first nitride semiconductor layer2and the mask layer3inFIG. 1). Thus, the second nitride semiconductor layer4is designed to have such a thickness as to be 50 μm or more, preferably 200 μm or more after polishing. Also, taking into consideration the easiness of cleavage, etc. after the formation of devices, the thickness of the second nitride semiconductor layer4after polishing is preferably 1 mm or less.

After the formation of the second nitride semiconductor layer4, layers ranging from the base substrate1to the mask layer3are removed by grinding, dissolving (wet etching), dry etching, etc. The resultant self-supported nitride semiconductor substrate is preferably mirror-polished on both surfaces. This is because if a crystal substrate had a rough surface, a crystal epitaxially grown thereon would also have a rough surface despite that the substrate is an ideal crystal with a low dislocation density, resulting in drastic decrease in the yield of devices in their production process, particularly at a photolithography step.

The nitride semiconductor usable in the present invention is not restricted, and it may be represented, for instance, by the general formula: InxGayAl1−x−yN, wherein 0≦x≦1, 0≦y≦1, and 0≦x+y≦1. A p-type GaN properly doped with Mg, etc. may also be used.

Because a nitride semiconductor layer having less lattice defects can be grown on the self-supported nitride semiconductor substrate of the present invention, epitaxial wafers for high-performance devices such as LEDs, LDs, light-receiving devices can be formed. Particularly, light-emitting devices such as LEDs and LDs formed by using the self-supported nitride semiconductor substrate of the present invention provide high emission power at a low driving voltage.

The present invention will be described in detail referring to Examples below without intention of limiting the present invention thereto.

REFERENCE EXAMPLE 1

To prove that even a light-emitting diode (LED) formed by using a GaN substrate having a small X-ray diffraction half width of a {0002} symmetric diffraction plane often has low brightness, each self-supported GaN substrate of Samples 1 to 9 was produced to form an LED shown inFIG. 2.

Each Sample of the self-supported GaN substrate was produced as follows. After forming a GaN buffer layer and a GaN layer on a 2-inch-diameter sapphire substrate, the sapphire substrate and the GaN buffer layer were removed. The resultant GaN substrate was polished on both surfaces to provide a 270-μm-thick self-supported GaN substrate. The formation of a GaN buffer layer and a GaN layer was conducted for each Sample with different production conditions of a heating temperature, etc.

The structure of LED formed on each self-supported GaN substrate was the same as in Example 8 below. Table 1 shows the relation between an X-ray diffraction half width of a (0002) plane of each self-supported GaN substrates of Samples 1 to 9 and the emission power of LED produced by using each self-supported GaN substrate. It is clear from Table 1 that even LEDs produced by using GaN substrates with a small X-ray diffraction half width of a (0002) plane do not necessarily provide high emission power.

A tubular reaction vessel made of quartz comprising a halogen gas supply tube and an N source supply tube was provided with a quartz boat containing a Ga metal at a position close to the halogen gas supply tube, and a 2-inch-diameter sapphire base substrate1fixing to a holder perpendicular to the reaction tube at a position separate from the quartz boat and close to the N source supply tube.

With the quartz boat containing a Ga metal heated at 900° C. and the sapphire base substrate1heated at 510° C., introduced into the tubular reaction vessel was an HCl gas together with a hydrogen carrier gas via the halogen gas tube, and an ammonia gas together with a nitrogen carrier gas via the N source supply tube. The HCl gas was reacted with Ga to form GaCl. Using the reaction of GaCl and NH3, a GaN buffer layer was grown to a thickness of 30 nm.

With the base substrate1having the GaN buffer layer formed thereon heated to 1050° C., a GaN crystal was grown from GaCl and ammonia as source gases at a rate of 24 μm/hr for 10 minutes, to form a first undoped GaN layer2having a thickness of 4 μm. The dislocation density of the first GaN layer2was about 109per cm2. A wafer was then taken out of the tubular reaction vessel. An SiO2film was formed as a mask layer3on the first GaN layer2, and provided with openings31having an area of 0.1 μm2at a density of 107per cm2by photolithography.

The resultant wafer was fixed to a holder in an HVPE apparatus. With the quartz boat containing a Ga metal heated at 900° C. and the wafer heated at 1050° C., supplied to the HVPE apparatus was an HCl gas together with a hydrogen carrier gas via the halogen gas tube, and an ammonia gas together with a nitrogen carrier gas via the N source supply tube. An HCl gas was react with Ga to generate GaCl. By the reaction of GaCl and NH3, GaN was grown on the SiO2film3at a rate of 100 μm/hr for 3 hours to form a second GaN layer4having a thickness of 300 μm. The wafer thus obtained had a structure shown inFIG. 1.

The wafer having the second GaN layer4formed thereon was taken out of the tubular reaction vessel, and the sapphire base substrate1to the SiO2film3were removed by lapping and polishing using a diamond polishing agent to provide a 300-μm-thick, self-supported GaN substrate. The self-supported GaN substrate thus obtained was free from cracks, etc. after any of growing and grinding.

X-ray was generated at 40 kV and 45 mA using a CuKα1as an X-ray source, to measure X-ray diffraction half widths of a (20-24) plane and a (11-24) plane of the self-supported GaN substrate. As a result, they were 278 seconds and 286 seconds, respectively. It is clear from these results that the self-supported GaN substrate of this Example has excellent crystallinity.

It was found by secondary ion mass spectrometry (SIMS) that this self-supported GaN substrate contained about 5×1017of Si per cm3as impurity, and that the content of Mg was less than the detection limit. It is presumed that Si was introduced from HCl as a source gas and from the tubular reaction quartz vessel.

COMPARATIVE EXAMPLE 1

A self-supported GaN substrate was produced in the same manner as in Example 1 except for growing a second GaN layer4doped with Si in a proportion of 2×1020per cm3. The X-ray diffraction half widths of a (20-24) plane and a (11-24) plane of GaN were 550 and 568 seconds, respectively, proving that this self-supported GaN substrate had extremely poorer crystallinity than that of the self-supported GaN substrate of Example 1.

COMPARATIVE EXAMPLE 2

A self-supported GaN substrate was produced in the same manner as in Example 1 except for growing a second GaN layer4doped with Mg in a proportion of 2×1020per cm3. The X-ray diffraction half widths of a (20-24) plane and a (11-24) plane of GaN were 820 and 845 seconds, respectively, proving that this self-supported GaN substrate had extremely poorer crystallinity than that of the self-supported GaN substrate of Example 1.

A self-supported GaN substrate was produced in the same manner as in Example 1 except for using a GaAs base substrate in place of the sapphire base substrate. The X-ray diffraction half widths of a (20-24) plane and a (11-24) plane of GaN were 322 and 336 seconds, respectively, proving that this self-supported GaN substrate had relatively good crystallinity, though slightly poorer than that of Example 1.

A 2-inch-diameter sapphire (C plane) base substrate1was set in a tubular reaction vessel of an MOVPE apparatus. After the inside of the vessel was substituted with hydrogen, the temperature of the base substrate1was elevated to 1050° C. while flowing hydrogen, to conduct the cleaning of the base substrate1. The temperature of the base substrate1was then lowered to 510° C., and a 30-nm-thick GaN buffer layer was formed on the base substrate1using hydrogen as a carrier gas and TMG and ammonia as source gases.

Elevating the substrate temperature to 1050° C., and using TMG and ammonia as source gases, a GaN crystal was grown at a speed of 4 μm/hr for 1 hour to form a first non-doped GaN layer2having a thickness of 4 μm. The first GaN layer2had a dislocation density of about 1×108/cm2.

After the formation of the first GaN layer, the wafer was taken out of the tubular reaction vessel, and an SiO2film was formed on the first GaN layer, and provided with openings having an area of 1 μm2at a density of 1×106/cm2by photolithography.

The resultant wafer was introduced into an HVPE apparatus, and fixed to a holder. With a quartz boat containing a Ga metal heated at 900° C. and the wafer heated at 1050° C., supplied to the HVPE apparatus were an HCl gas together with a hydrogen carrier gas via a halogen gas tube, and an ammonia gas together with a nitrogen carrier gas via an N source supply tube near the sapphire base substrate1. The HCl gas was reacted with Ga to form GaCl, and a GaN crystal was grown by the reaction of GaCl and ammonia at a speed of 100 μm/hr for 3 hours, to form a second GaN layer4having a thickness of 300 μm.

The sapphire base substrate1to the SiO2film3were removed by lapping and polishing in the same manner as in Example 1 to obtain a 300-μm-thick, self-supported GaN substrate. The X-ray diffraction half widths of a (20-24) plane and a (11-24) plane of this self-supported GaN substrate were 120 and 136 seconds, respectively. This proves that a self-supported GaN substrate with good crystallinity was obtained.

A self-supported GaN substrate was produced in the same manner as in Example 3 except that the second GaN layer4was grown using a TiN film in place of an SiO2film. The X-ray diffraction half widths of a (20-24) plane and a (11-24) plane of this self-supported GaN substrate were 102 and 104 seconds, respectively, proving that a self-supported GaN substrate having better crystallinity than that of Example 3 was obtained.

A self-supported GaN substrate was produced in the same manner as in Example 3 except that the second GaN layer4was grown using a Mo film in place of the SiO2film. The X-ray diffraction half widths of a (20-24) plane and a (11-24) plane of this self-supported GaN substrate were 203 and 211 seconds, respectively, proving that a self-supported GaN substrate having better crystallinity than that of Example 1 was obtained.

A quartz boat containing a Ga metal was disposed in a tubular reaction vessel made of quartz comprising a halogen gas supply tube and an N source supply tube, at a position close to the halogen gas supply tube, and a 2-inch-diameter sapphire base substrate1perpendicular to the reaction tube was fixed to a holder at a position separate from the quartz boat and close to the N source supply tube.

With the quartz boat containing a Ga metal heated at 900° C. and the sapphire base substrate1heated at 510° C., supplied to the reaction vessel were an HCl gas together with a hydrogen carrier gas via the halogen gas tube, and an ammonia gas together with a nitrogen carrier gas via the N source supply tube. The HCl gas was reacted with Ga to form GaCl. A GaN buffer layer was grown by the reaction of GaCl and NH3to a thickness of 30 μnm on the sapphire base substrate1.

With the temperature of the base substrate1having the buffer layer formed thereon elevated to 1050° C., a GaN crystal was grown at a speed of 100 μm/hr for 2 hours using the formed GaCl and ammonia as source gases, to form a first non-doped GaN layer2having a thickness of 200 μm. The first GaN layer2had a dislocation density of about 1×106/cm2.

After the growth of the first GaN layer2, the wafer was taken out of the reaction vessel. After the formation of an SiO2film3on the first GaN layer2, the SiO2film3was provided with openings31having an area of 10 μm2at a density of 1×104/cm2by photolithography.

The resultant wafer was fixed to a holder in the HVPE apparatus. With the quartz boat containing a Ga metal heated at 900° C. and the wafer heated at 1050° C., supplied to the HVPE apparatus were an HCl gas together with a hydrogen carrier gas via the halogen gas tube, and an ammonia gas together with a nitrogen carrier gas via the N source supply tube. The HCl gas was reacted with Ga to form GaCl. GaN was grown on the SiO2film3by the reaction of GaCl and NH3at a speed of 100 μm/hr for 3 hours, to form a second GaN layer4having a thickness of 300 μm.

The sapphire base substrate1to the SiO2film3were removed by lapping and polishing in the same manner as in Example 1, to obtain a self-supported GaN substrate having a thickness of 300 μm. The X-ray diffraction half widths of a (20-24) plane and a (11-24) plane of this self-supported GaN substrate were 50 and 67 seconds, respectively. This proves that a self-supported GaN substrate with good crystallinity was obtained.

A self-supported GaN substrate was produced in the same manner as in Example 6 except that a second GaN layer4was formed with the density of the openings31of the SiO2film3changed from 1×104/cm2to 1×103/cm2. The X-ray diffraction half widths of a (20-24) plane and a (11-24) plane of this self-supported GaN substrate were 26 and 32 seconds, respectively. This proves that a self-supported GaN substrate with good crystallinity was obtained.

Table 2 shows the measurement results of the X-ray diffraction half widths of the self-supported GaN substrates in a (20-24) plane and a (11-24) plane in Examples 1 to 7 and Comparative Examples 1, 2.

As shown inFIG. 2, an epitaxial layer having a light-emitting nitride device structure was formed on each self-supported GaN substrate101obtained in Examples 1 to 7 and Comparative Examples 1 to 2 by a metal-organic chemical vapor deposition (MOCVD) method, to produce an LED device. Trimethyl gallium (TMG), trimethyl aluminum (TMA), trimethyl indium (TMI), and bis(cyclopentadienyl) magnesium (Cp2Mg) were used as organometallic materials, and ammonia (NH3) and silane (SiH4) were used as gas materials. Hydrogen and nitrogen were used as a carrier gas.

First, a 4-μm-thick n-GaN contact layer102doped with 1×1019of Si per cm3was grown on the self-supported GaN substrate101at 1050° C. An InGaN active layer110having a multiquantum well (MQW) structure constituted by an alternate laminate of three 3-nm-thick quantum well layers111each made of In0.1Ga0.9N and four 10-nm-thick GaN barrier layers112was then grown on the contact layer102at 800° C. A 30-nm-thick p-Al0.1Ga0.9N clad layer121and a 200-nm-thick p-GaN contact layer122were formed in this order on the active layer.

After the wafer having the above layers was taken out of the MOVPE apparatus, a positive electrode125containing Ni and Au was formed on the p-GaN contact layer122, and a negative electrode124of Ti and Al was formed on a rear surface of the GaN substrate101. Finally, the wafer was cut to chips of 350 μm each to provide LED devices. 20 mA of a forward current was supplied to each LED device sample to emit a blue-purple laser beam of 405 nm. The emission power and the driving voltage of each LED device sample are shown in Table 3.

With respect to each LED device sample of 1 to 9, the relations between the X-ray diffraction half widths of a (20-24) plane and a (11-24) plane and the emission power are shown inFIGS. 3 and 4. It is clear fromFIGS. 3 and 4that the LED devices of Samples 1 to 7, in which the X-ray diffraction half widths of a (20-24) plane and a (11-24) plane of the self-supported GaN substrate had 500 seconds or less, had emission power more than two times that of the LED devices of Samples 8, 9, in which the corresponding X-ray diffraction half widths had more than 500 seconds. The driving voltage of the LED device was high when the self-supported GaN substrate had an X-ray diffraction width of more than 500 seconds in a (20-24) plane and a (11-24) plane.

Using the self-supported nitride semiconductor substrate of the present invention, nitride semiconductor layers with little lattice defects can be grown for devices such as LEDs, LDs, light-receiving devices, etc. with drastically improved characteristics. Light-emitting devices formed by using such self-supported nitride semiconductor substrates can provide high emission power with low driving voltage.