JP4069949B2 - Semiconductor element - Google Patents

Description

  The present invention is a light emitting element using a short wavelength such as a light emitting diode or a laser diode using III-V nitride, a light receiving element such as a photodiode, and a high temperature operating in a high temperature environment. The present invention relates to a semiconductor element such as a semiconductor element or a high-speed operation semiconductor element.

  III-V nitrides with a wurtzite crystal structure are direct transition type semiconductors with a wide forbidden band, so they are attracting attention as materials for short-wavelength light-emitting and light-receiving elements, as well as high-temperature and high-speed semiconductor elements. Has been. Group III-V nitrides having such a wurtzite crystal structure include gallium nitride (GaN), aluminum nitride (AlN), boron nitride (BN), indium nitride (InN), and mixed crystals thereof. The forbidden band width can be changed by changing the material difference or the composition ratio of the mixed crystal.

  In particular, gallium nitride and mixed crystals thereof are actively studied as light emitting device materials. Recently, blue and blue-green LEDs (light-emitting diodes) using gallium nitride compound semiconductors have been put into practical use, and as a next step, short-wavelength LDs (laser diodes) used in high-density optical disk readers and the like are put into practical use. Is expected.

By the way, when a semiconductor element such as an LED or LD is formed, it is necessary to grow a semiconductor single crystal film on the same type of single crystal substrate. Since single crystals could not be synthesized, conventionally, heteroepitaxial growth in which a group III-V nitride single crystal film is grown on a different substrate has been used. As a substrate for this heteroepitaxial growth, (0001) plane (C plane) or (11-20) plane (A plane) of sapphire single crystal, (111) plane of Si single crystal, 6H-SiC single crystal ( The (0001) plane, the (111) plane of MgAl ₂ O ₄ single crystal, and the like are known.

  Among these, the sapphire single crystal substrate is capable of growing a single crystal film of a gallium nitride compound semiconductor having good crystallinity through a low-temperature growth buffer layer and is relatively inexpensive. Most commonly used for blue and blue-green LEDs using a compound semiconductor.

However, in particular, LDs in the infrared region using GaAs-based compound semiconductors and InP-based compound semiconductors have been put into practical use, but blue-emitting LDs using III-V nitrides are still in the research stage. Several research reports have been made. For example, Jpn. J. Appl. Phys.,
Vol. 35 (1996) PP. L74-L76, Jpn. J. Appl. Phys., Vol. 35 (1996) PP. L217-L220, and Appl. Phys.
Lett., Vol. 68, No. 15 (1996) PP. 2105 to 2107, etc., all of which are pulse oscillations.

  Further, as continuous oscillation, there is a report in Appl. Phys. Lett., Vol. 69, No. 26 (1996) PP. 4056 to 4058, but the lifetime is short because of the temperature rise during continuous oscillation. The reason is that since the single crystal substrate used is not a III-V group nitride, the difference in lattice constant and the coefficient of thermal expansion is large between the III-V nitride single crystal film on the substrate and the crystal This is because it is difficult to synthesize a group III-V nitride single crystal film having good properties, and many defects such as dislocations are included in the single crystal film.

  Thus, although application as a light-emitting element has been realized in part, high-temperature semiconductor elements and high-speed semiconductor elements have not yet been put into practical use. This is also because many defects such as dislocations are included in the group III-V nitride single crystal film. At high temperatures, dislocations multiply and degrade performance significantly, shortening the lifespan, and these dislocations reduce carrier mobility, making it difficult to achieve high-speed operation.

  For this reason, attempts have been made to improve the film quality by introducing a low-temperature growth buffer layer, but the improvement has not been made sufficiently. Further, since it is difficult to cleave the single crystal substrate to be used, there is a problem that the flatness of the resonance surface cannot be ensured when forming the LD, and the formation process of the resonance surface is complicated.

As a method for solving the above problems, an attempt to use a gallium nitride single crystal, which is a group III-V nitride, as a single crystal substrate is described in Jpn.
J. Appl. Phys., Vol. 35 (1996) PP.L77-L79. However, the gallium nitride single crystal that can be synthesized at present is as small as about 2 mm square, and it is difficult to put it into practical use as a semiconductor element such as an LD capable of continuous oscillation.

Furthermore, light emitting elements, especially LDs, generate a large amount of heat during light emission, and high-speed semiconductor elements generate a large amount of heat during high-speed operation. Therefore, even high-temperature semiconductor elements suppress deterioration of the element, so it is necessary to improve heat dissipation. Therefore, it is desirable to use a substrate having a large thermal conductivity. However, any of the substrates such as sapphire, Si, and MgAl ₂ O ₄ that can grow a necessary single crystal film has a low thermal conductivity. For this reason, elements that require high output and temperature stability use these substrates bonded to a heat sink material. In Jpn. J. Appl. Phys., Vol. 34 (1995) PP. L1517 to L1519, an element in which a GaN layer is formed on an sapphire single crystal substrate via an AlN film is proposed. Since the single crystal is used as the substrate, the above heat dissipation problem is not solved.

  As an example in which a semiconductor material is grown on a substrate having a high thermal conductivity, a semiconductor single crystal film is formed on a diamond single crystal substrate as disclosed in JP-A No. 64-42813. is there. This relates to a thin film single crystal substrate in which at least one single crystal layer made of at least one material selected from gallium nitride, indium nitride, aluminum nitride, etc. is formed on a diamond single crystal substrate. An object of the present invention is to provide a substrate having a high rate, a low thermal expansion coefficient, and excellent heat resistance and environmental properties. However, this diamond single crystal substrate is also not sufficiently matched in lattice constant and thermal expansion coefficient with the III-V nitride single crystal.

Jpn. J. Appl. Phys., Vol. 35 (1996) PP. L74-L76. Jpn. J. Appl. Phys., Vol. 35 (1996) PP. L217-L220 Appl. Phys. Lett., Vol. 68, No. 15 (1996) PP. Appl. Phys. Lett., Vol. 69, No. 26 (1996) PP. 4056-4058. Jpn. J. Appl. Phys., Vol. 35 (1996) PP. L77-L79. Jpn. J. Appl. Phys., Vol. 34 (1995) PP. L1517-L1519 JP-A 64-42813

As described above, substrate materials such as sapphire, Si, SiC, and MgAl ₂ O ₄ that have been conventionally used for the growth of group III-V nitride single crystal films have lattice constants and thermal Insufficient expansion coefficient matching. For this reason, it is difficult to synthesize a group III-V nitride single crystal film having good crystallinity on these substrates, and at present, it is indispensable to form a low-temperature growth buffer layer with the substrate. .

  Further, each of the single crystal substrates other than the above-described conventionally used SiC cannot be cleaved for forming the resonance surface of the LD. There is an attempt to form a cleavage plane by etching, but there is a drawback that a sufficiently flat resonance surface cannot be obtained and the formation process is complicated. Further, when SiC is used as the substrate, the cause is not clear, but there is a problem that the light emission characteristics are poor due to the stress accompanying the difference in thermal expansion coefficient or the diffusion of the SiC component into the GaN film. . Furthermore, the sapphire substrate that has been most commonly used in the past has a very low thermal conductivity, and it has been necessary to bond it to a heat sink in order to use it for a light emitting device or the like. Moreover, since sapphire has no electrical conductivity, it has been difficult to handle the electrodes when bonding to the heat sink.

  As described in Jpn. J. Appl. Phys., Vol. 35 (1996) PP. L77-L79, if a single crystal substrate of gallium nitride is used, a high-quality III-V nitride single crystal film can be obtained. Synthesis is possible. However, the gallium nitride single crystal used for the substrate is currently difficult to increase in size, has a low thermal conductivity, and is inferior in heat dissipation. Further, the technique described in the above Japanese Patent Application Laid-Open No. 64-42813 uses a diamond single crystal substrate having a high thermal conductivity for the purpose of heat dissipation. There was a problem that the matching of the expansion coefficients was not sufficient.

  In view of such a current situation, the present invention uses a substrate having a lattice constant and a thermal expansion coefficient matching with those of III-V nitrides, and has a cleavage plane, a good thermal conductivity, and a relatively large single crystal. A short-wavelength light-emitting element capable of continuous oscillation using a group III-V nitride, by growing a group III-V nitride single crystal film having good crystallinity on the substrate, An object of the present invention is to provide a semiconductor element such as a light receiving element, a high temperature semiconductor element or a high speed semiconductor element.

  In order to achieve the above object, a semiconductor device provided by the present invention includes a group III nitride single crystal substrate containing a transition metal of 10 ppb or more and 0.1 mol% or less, and a nitride formed directly on the single crystal substrate. A semiconductor device comprising: a single crystal film of at least one group III-V nitride selected from gallium, aluminum nitride, boron nitride, indium nitride, and mixed crystals made of these materials, wherein the single crystal There is no precipitate of transition metal or nitride or oxide thereof in the substrate, or the precipitate does not affect the characteristics of the semiconductor element formed on the single crystal substrate. The group III nitride single crystal substrate is preferably an aluminum nitride substrate.

  Further, another semiconductor element provided by the present invention contains an aluminum nitride single crystal substrate containing 10 ppb or more and 0.1 mol% or less of a transition metal, and no precipitation of the transition metal or a nitride or oxide thereof, A single crystal film of at least one group III-V nitride selected from gallium nitride, aluminum nitride, boron nitride, indium nitride and a mixed crystal made of these materials formed directly on the single crystal substrate; And intentionally adding at least one of silicon, tin, oxygen, sulfur, selenium, and tellurium to a part of the single crystal film to give n-type conductivity, or zinc, beryllium, magnesium, potassium At least one of these is intentionally added to give p-type conductivity.

  Still another semiconductor element provided by the present invention includes an aluminum nitride single crystal substrate containing 10 ppb or more and 0.1 mol% or less of a transition metal, and no precipitation of the transition metal or a nitride or oxide thereof, And a single crystal film of at least one group III-V nitride selected from gallium nitride, aluminum nitride, boron nitride, indium nitride, and a mixed crystal made of these materials formed directly on a crystal substrate. The length and width of the single crystal substrate are both 10 mm or more and the thickness is 300 μm or more.

  The semiconductor element in the present invention includes a light emitting element, a light receiving element, a high temperature semiconductor element, a high speed semiconductor element, and the like. In particular, the light emitting element includes a light emitting diode (LED) and a laser diode (LD). Particularly in the case of LD, the resonance surface can be formed by cleaving an aluminum nitride single crystal substrate and a group III-V nitride single crystal film. In that case, the (10-10) plane or the (11-20) plane of the group III-V nitride single crystal film is used as the cleavage plane, and for that purpose, the (0001) plane of the aluminum nitride single crystal is used as the substrate. Alternatively, the (0001) plane of the group III-V nitride single crystal film is used as the cleavage plane, and for this purpose, the (10-10) plane or the (11-20) plane of the aluminum nitride single crystal is used as the substrate. It is advantageous.

  Further, in the present invention using an aluminum nitride single crystal as a substrate, it has been necessary to grow a group III-V nitride single crystal film having excellent crystallinity and film surface smoothness. It is also possible to eliminate the low-temperature growth buffer layer of group nitride and form a semiconductor element by directly forming a group III-V nitride single crystal film on the aluminum nitride single crystal substrate.

  According to the present invention, by using a large-sized aluminum nitride single crystal substrate having a lattice constant and a thermal expansion coefficient matching with those of III-V nitrides, having a cleavage plane, and having good heat dissipation, on top of it. Group III-V nitride single crystal film having good crystallinity can be grown, and a semiconductor device using group III-V nitride, for example, a short wavelength light emitting device, a light receiving device, and a high temperature semiconductor device capable of continuous oscillation High-speed semiconductor elements can be provided.

  In addition, according to the present invention, a low-temperature growth buffer layer, which has been conventionally required, can be dispensed with, and a semiconductor device with excellent heat dissipation that does not require a heat sink can be provided. It becomes possible to realize a light emitting element such as a light emitting diode or a laser diode using a laser, and in a laser diode, a resonator can be made by using cleavage of a substrate.

  The present invention uses aluminum nitride (AlN) as a substrate, which has a lattice constant and a thermal expansion coefficient close to those of III-V nitrides, has a good thermal conductivity, and provides a relatively large single crystal. A single crystal film having excellent crystallinity is formed by growing a group III-V nitride on a single crystal substrate to realize a semiconductor device such as a light emitting device suitable for light emission at a short wavelength.

  In general, in order to realize a semiconductor element such as a light emitting element, it is necessary to use a large single crystal substrate so that the manufacturing cost can be reduced. Group III-V nitride single crystals do not naturally occur and must be artificially synthesized. Conventionally, single crystals of boron nitride, gallium nitride, and aluminum nitride have been artificially synthesized. Among these, a relatively large aluminum nitride single crystal can be synthesized stably and inexpensively, so that it is suitable as a substrate for forming a semiconductor element.

  In addition, the present inventors proposed a method for producing a larger and higher quality nitride single crystal as Japanese Patent Application No. 8-141236. In this method, a powder of nitride such as AlN is mixed with an oxide powder that reacts with the nitride under heating to decompose and vaporize the powder, and the mixed powder is mixed in a nitrogen atmosphere or with hydrogen and / or carbon. Heating at a temperature lower than the sublimation temperature or melting temperature of the nitride in a nitrogen atmosphere, the nitride powder is decomposed and vaporized by reaction with the oxide powder, and this decomposed and vaporized component is crystal-grown on the substrate from the gas phase Thus, a nitride such as AlN is obtained.

By this method, an aluminum nitride single crystal having a size that can be practically used as a bulk material, specifically, a length and width of both 10 mm or more and a thickness of 300 μm or more can be manufactured. The aluminum nitride single crystal is optimal as a substrate for the semiconductor device of the present invention. In particular, it is preferable to use an oxide of an IVa group or a Va group element, especially TiO ₂ powder, as the oxide powder mixed with the AlN powder. In this case, 90 mol% or more of the components other than nitrogen obtained is Al. A high-quality aluminum nitride single crystal having an oxygen content of 500 ppm or less is particularly preferable as the substrate of the semiconductor element of the present invention.

  The crystallinity of such an aluminum nitride single crystal is preferably 1.5 minutes or less as the full width at half maximum of the rocking curve in X-ray diffraction. If a single crystal substrate having a full width at half maximum exceeding 1.5 minutes is used, the lifetime of the semiconductor element There is a tendency to reduce the performance. Further, the thickness of the aluminum nitride single crystal as the substrate is preferably 300 μm or more, and if it is less than 300 μm, the crystallinity tends to be lowered.

  The aluminum nitride single crystal preferably contains 10 ppb or more and 0.1 mol% or less of a transition metal, and the transition metal is particularly preferably titanium. The transition metal easily binds to oxygen that degrades the performance of the semiconductor element, captures a small amount of oxygen impurities in the single crystal, and makes it difficult for oxygen to diffuse from the single crystal substrate to the semiconductor element. Suppress performance degradation. However, when the transition metal content is less than 10 ppb, this effect is not observed. When the transition metal content exceeds 0.1 mol%, the transition metal and its nitrides and oxides precipitate as foreign substances in the single crystal. The crystallinity of the crystal is impaired.

Light-emitting elements using III-V nitrides, especially LEDs and LDs, are required to have good crystallinity in order to improve the characteristics (emission intensity, lifetime, etc.) of the light-emitting elements. It is known that the crystallinity of a single crystal film formed on a single crystal substrate is improved as the lattice constant and the thermal expansion coefficient of the single crystal substrate and the single crystal film are closer. Since the aluminum nitride used as the substrate in the present invention is a group III-V nitride itself, it constitutes a single crystal film compared to sapphire, Si, SiC, and MgAl ₂ O ₄ conventionally used as substrates. Lattice constants and thermal expansion coefficients are close to those of III-V nitrides.

  Therefore, the group III-V nitride film formed on the aluminum nitride single crystal substrate has good crystallinity, and the characteristics of the light-emitting element of the present invention using this film are improved compared to those of the conventional structure. For this reason, in the prior art, in order to obtain a single crystal film of group III-V nitride with good crystallinity on a heterogeneous substrate, it was indispensable to form a low temperature growth buffer layer. There is no need to provide.

  Further, among the light emitting elements, the LD needs to form a resonance surface in its structure. Since the resonance surface is required to have high flatness, formation by cleavage is preferable. In the present invention, since the group III-V nitride single crystal film is formed on the aluminum nitride single crystal substrate, the crystal plane orientations of both are aligned, and the cleavage planes also coincide. Therefore, unlike the case of a conventional sapphire substrate or the like, the resonance surface can be easily formed by cleaving the single crystal substrate and the single crystal film.

  In this case, it is particularly preferable to use (0001), (10-10), or (11-20) plane substrates as the aluminum nitride single crystal substrate. In the case of a (0001) plane substrate, element formation is facilitated by forming a resonant surface using the (10-10) plane or the (11-20) plane as a cleavage plane perpendicular to the substrate plane. In the case of the (10-10) plane substrate, the (0001) plane or the (1-210) plane is cleaved, and in the case of the (11-20) plane substrate, the (0001) plane or the (1-100) plane is cleaved. By forming the resonance surface used as a surface perpendicular to the substrate surface, element formation is facilitated. When a substrate having a plane orientation other than that is used, the cleavage plane is inclined with respect to the substrate, so that it is difficult to handle the device when forming the element.

  Among these, it is preferable to use a (10-10) plane substrate or a (11-20) plane substrate. In the case of a (0001) plane substrate, a cleavage plane exists every 30 ° rotation, so that the cleavage plane is not clean and it is difficult to form a flat resonance surface, whereas the (10-10) plane This is because the cleavage plane is rotated by 90 ° between the substrate and the (11-20) plane substrate, and a clean resonance surface can be formed relatively easily.

Furthermore, light emitting elements using III-V nitrides, especially LEDs and LDs, and high-speed operating semiconductor elements are expected to have high driving power, and high-temperature semiconductor elements are also particularly effective in reducing heat damage. A good structure is required. Aluminum nitride has an extremely large thermal conductivity compared to sapphire, MgAl ₂ O _{4 and the} like that have been used as conventional substrates. Therefore, when the semiconductor element is formed, heat dissipation is good, and a heat sink is used separately from the substrate. There is no need. Therefore, the cost can be reduced as compared with the case where these conventional substrate materials are used. In particular, an LD using a III-V compound has a large oscillation threshold current and driving voltage, and is expected to generate a very large amount of heat, so that the structure of the present invention is extremely effective.

  In the aluminum nitride substrate used in the present invention, a group III-V nitride single crystal film is used to grow a group III-V nitride single crystal film having excellent crystallinity and film surface smoothness. The surface roughness of the surface to be formed is preferably 0.1 μm or less.

A group III-V nitride single crystal film grown on an aluminum nitride single crystal substrate is a group III-V nitride having a wurtzite crystal structure, such as GaN, AlN, BN and InN, and Al _x Ga _{(1- x)} N, In _x Ga _(1-x) N, B _x Ga _(1-x) N, B _x Al _(1-x) N, In _x Al _(1-x) N, B _x In _{(1- x)} A mixed crystal such as N. In the case of a mixed crystal, in addition to the ternary mixed crystal given as an example, a quaternary or even multi-element mixed crystal may be used.

As a method for growing these III-V nitride single crystal films on an aluminum nitride single crystal substrate, an MBE method (Molecular
Used to form a single crystal film on a substrate such as Beam Epitaxy method (MOB), MOCVD (Metal Organic Chemical Vapor Deposition method), sputtering method, vacuum deposition method, etc. A known method can be used. In order to grow a single crystal film by these methods, it is necessary to heat the substrate to a high temperature, and the substrate temperature at which the single crystal film can be grown varies depending on the type of film to be grown and the film formation method, but III-V In the group nitride single crystal film, the temperature is preferably between 500 ° C. and 1300 ° C.

  As described above, the group III-V nitride single crystal film can be grown on the aluminum nitride substrate without the intervention of the low temperature growth buffer layer. However, in order to grow a group III-V nitride single crystal film excellent in crystallinity and film surface smoothness, a low temperature growth buffer layer of group III-V nitride is formed on the substrate, and on this, It is desirable to form a single crystal film. When a low temperature growth buffer layer is used, a III-V nitride having a wurtzite crystal structure can be used as the buffer layer, and in particular, a lattice-matched one is preferable, but it is not necessarily the same as the single crystal film grown on it. The material is not limited.

  As a method for forming the low temperature growth buffer layer, the same method as that for forming the group III-V nitride single crystal film described above may be used, but the substrate temperature is set lower than that for growing the single crystal film. It is necessary to grow an amorphous or polycrystalline film. The substrate temperature for forming the low-temperature growth buffer layer varies depending on the type of film to be grown and the film forming method, but is generally between 20 ° C. and 900 ° C. The low-temperature growth buffer layer is amorphous or polycrystalline when formed, but often changes to a single crystal when the substrate temperature is increased to form a single crystal film thereon.

  A group III-V nitride single crystal film in a semiconductor element is usually used with conductivity controlled by addition of impurities. That is, in the group III-V nitride single crystal film of the present invention, n-type conductivity can be obtained by adding at least one selected from silicon, tin, oxygen, sulfur, selenium, tellurium, etc. as impurities, or It is possible to impart p-type conductivity by adding at least one selected from zinc, beryllium, magnesium, potassium and the like. Similarly to the III-V nitride single crystal film, the low temperature growth buffer layer can also be used with its conductivity controlled by adding impurities.

  As described above, the group III-V nitride single crystal film 2 is formed on the aluminum nitride single crystal substrate 1 as shown in FIG. 1, and the band gap is further changed by changing the composition ratio of materials and mixed crystals. A semiconductor element of the present invention such as a light emitting diode or a laser diode can be formed by forming a structure in which single crystal films of group III-V nitrides having different thicknesses are stacked and providing predetermined electrodes.

[Example 1]
First, an aluminum nitride single crystal as a substrate was manufactured as follows. Mix 99% purity AlN powder and 99% purity TiO ₂ powder so that the molar ratio of TiO ₂ to AlN is 0.75, perform ultrasonic mixing in ethanol, and then remove ethanol by drying. To obtain a mixed powder. Meanwhile, a 10 mm square c-plane cut β-type SiC single crystal plate was prepared as a substrate for crystal growth.

  The mixed powder and the SiC single crystal substrate were placed in a heating furnace as shown in FIG. That is, the heating furnace 3 includes an induction heating coil 4 and a heat insulating material muffle 5, a container-shaped graphite crucible 6 having a lid is disposed inside the heat insulating material muffle 5, and a BN crucible without a lid is disposed inside the container. 7 is provided. In addition, an atmosphere gas inlet 8 a and an outlet 8 b are provided in the upper part of the heating furnace 3. In the BN crucible 7 of the heating furnace 3, the compressed mixed powder 9 was placed, and the substrate 10 of the SiC single crystal plate was set to face the upper side.

  After the inside of the heating furnace 3 is once evacuated, nitrogen gas is introduced from the inlet 8a to set the inside of the furnace to 1 atm (760 Torr), and the periphery of the mixed powder 9 is lower than the decomposition temperature of AlN (2200 ° C.) by induction heating While heating to 1800 ° C., the periphery of the substrate 10 was heated to 1700 ° C. and maintained for 24 hours by controlling the heating unit. As a result of spectral analysis of the gas phase components in the heating furnace 3 at this time, the oxygen partial pressure was 0.05 Torr, and the ratio Pr / Po of the carbon partial pressure (Pr) and the oxygen partial pressure (Po) was 2.0. .

  As a result, a transparent amber aluminum nitride of 10 mm square and a thickness of 8200 μm grows on the lower surface of the substrate 10 made of a SiC single crystal plate, and is a single crystal of aluminum nitride by crystallinity evaluation by X-ray diffraction. It could be confirmed. As a result of the composition analysis, the Al content was 92 mol%, the oxygen content was 350 ppm, carbon was 8 mol%, and Ti was 0.02 mol%.

The surface of the aluminum nitride single crystal obtained as described above is polished flat, washed with an organic solvent, and its (0001) plane is used as a substrate, and In _0.1 G _{0. 5} having the structure shown in FIG _. A light emitting diode (LED) having ₉ N as an active layer was formed. That is, the above-described aluminum nitride substrate 11 is used, an n-type GaN single crystal film 12 is formed on the surface of the aluminum nitride substrate 11 via an n-type GaN low-temperature growth buffer layer 13, and n-type In _0.1 G _{0 is} further formed. _.9 N single crystal film 14 and p-type GaN single crystal film 15 are sequentially formed, and electrodes 16 and 17 are formed, whereby a light emitting diode (LED) having In _0.1 G _0.9 N as an active layer. Formed.

The growth of each group III-V nitride single crystal film was performed as follows under atmospheric pressure using MOCVD. The first n-type GaN low-temperature growth buffer layer 13 has H ₂ as a carrier gas at a flow rate of 10 l / min and NH ₃ , trimethyl gallium, and SiH ₄ (H ₂ diluted, concentration 10 ppm) as source gases at 4.0 l / min. Introduced into the reaction chamber at a flow rate of min, 30 μmol / min, 4 nmol / min, held at a substrate temperature of 500 ° C. for 1 minute, and formed an n-type GaN low-temperature growth buffer layer 13 on the aluminum nitride single crystal substrate 11 with a film thickness of 25 nm. Only grown. Next, the substrate temperature was raised to 1000 ° C. while maintaining the introduced gas, and the n-type GaN single crystal film 12 was grown on the low temperature growth buffer layer 13 to a thickness of 4 μm in 60 minutes.

Subsequently, the substrate temperature is set to 800 ° C., N ₂ gas is used as a carrier gas at a flow rate of 10 l / min, and NH ₃ , trimethylindium, trimethylgallium, and SiH ₄ (H ₂ diluted, concentration 10 ppm) are each 4.0 l as source gases. / Min, 24 μmol / min, 2 μmol / min, and 1 nmol / min at a flow rate, the n-type In _0.1 G _0.9 N single crystal film 14 is placed on the n-type GaN single crystal film 12 for 7 minutes. The film was grown to a thickness of 20 nm. Further, the substrate temperature was set again to 1000 ° C., and the p-type GaN single crystal film 15 was grown on the n-type In _0.1 G _0.9 N single crystal film 14 to a thickness of 0.8 μm in 15 minutes. At this time, the gas used for the growth was the same as that used for the growth of the n-type GaN single crystal film 12 except that biscyclopentadiethyl magnesium was used at a flow rate of 3.6 μmol / min instead of SiH ₄ .

After each single crystal film was grown as described above, the entire substrate after the film growth was annealed at 700 ° C. in an N ₂ atmosphere. Thereafter, each nitride single crystal film was partially processed by reactive dry etching to expose part of the n-type GaN single crystal layer 12 on the surface. Finally, aluminum electrodes 16 and 17 were formed on the uppermost p-type GaN single crystal film 15 and the exposed n-type GaN single crystal film 12, respectively, by sputtering to form an LED.

Samples in the middle of each process were prepared and their crystal structures were evaluated using RHEED (high-speed reflected electron diffraction). As a result, the n-type GaN single crystal film 12, n-type In _0.1 G _0.9 Both the N single crystal film 14 and the p-type GaN single crystal film 15 are single crystal films having a wurtzite crystal structure, and each (0001) plane is parallel to the (0001) plane of the aluminum nitride single crystal substrate 11. Turned out to be growing.

  When the characteristics of the LED thus obtained were evaluated at room temperature, blue light emission having a peak wavelength at 440 nm was confirmed. Further, when this LED was allowed to emit light continuously for 1 hour, the temperature of the element did not increase so as to affect the element performance, and performance degradation such as a decrease in luminance did not occur.

[Example 2]
Using the (0001) plane of the same aluminum nitride single crystal as in Example 1 as a substrate, an In _0.2 Ga _0.8 N / In _0.05 Ga _0.95 N quantum well structure 27 having the structure shown in FIG. A laser diode (LD) having an active layer was formed.

That is, as shown in FIG. 4, an n-type GaN low-temperature growth buffer layer 23 is formed on the surface of the aluminum nitride substrate 21, followed by an n-type GaN single crystal film 22 and an n-type In _0.1 Ga _{0. 9} N single crystal film 24, n-type Al _0.15 Ga _0.85 N single crystal film 25, n-type GaN single crystal film 26, In _0.2 Ga _0.8 N / In _0.05 Ga _0.95 N Quantum well structure 27, p-type Al _0.2 Ga _0.8 N single crystal film 28, p-type GaN single crystal film 29, p-type Al _0.15 Ga _0.85 N single crystal film 30, p-type GaN single crystal A film 31 was formed, and electrodes 32 and 33 were formed to constitute an LD.

The growth of each group III-V nitride single crystal film was carried out using the MOCVD method under atmospheric pressure as follows. First, an n-type GaN low-temperature growth buffer layer 23 was grown on the aluminum nitride single crystal substrate 21 at a substrate temperature of 500 ° C. At that time, H ₂ was used as a carrier gas at a flow rate of 10 l / min, and NH ₃ , trimethyl gallium, and SiH ₄ (H ₂ diluted, concentration 10 ppm) were used as source gases at 4.0 l / min, 30 μmol / min, and 4 nmol / min, respectively. Was introduced into the reaction chamber at a flow rate of 25 nm and grown to a thickness of 25 nm.

Next, the substrate temperature was raised to 1000 ° C. while maintaining the introduced gas, and the n-type GaN single crystal film 22 was grown on the n-type GaN low-temperature growth buffer layer 23 to a thickness of 4 μm in 60 minutes. Thereafter, H ₂ gas as a carrier gas at a flow rate of 10 l / min, and NH ₃ , trimethylindium, trimethylgallium, SiH ₄ (diluted with H ₂ , concentration 10 ppm) as source gases are 4.0 l / min, 24 μmol / min, Introduced into the reaction chamber at a flow rate of 2 μmol / min and 1 nmol / min, an n-type In _0.1 Ga _0.9 N single crystal film 24 is grown on the n-type GaN single crystal film 22 to a thickness of 100 nm in 35 minutes. I let you.

Next, the substrate temperature was again set to 1000 ° C., and an n-type Al _0.15 Ga _0.85 N single crystal film was grown. That is, NH ₃ , trimethylaluminum, trimethylgallium, and SiH ₄ (H ₂ dilution, concentration 10 ppm) were used as source gases at a flow rate of 4.0 l / min, 6 μmol / min, 24 μmol / min, and 4 nmol / min, respectively, for 5 minutes. To a film thickness of 400 nm. Subsequently, an n-type GaN single crystal film 26 was grown on the n-type Al _0.15 Ga _0.85 N single crystal film 25. The growth conditions such as the source gas were the same as those of the previous n-type GaN single crystal film 22, and the film was grown to a thickness of 100 nm in 2 minutes.

Further, on the n-type GaN single crystal film 26, In _0.2 Ga _0.8 N / In _0.05 Ga _0.95 N was laminated to a thickness of 2.5 nm / 5.0 nm, respectively. A 26-period quantum well structure 27 was formed. At that time, the In _0.2 Ga _0.8 N layer is formed by using H ₂ gas as a carrier gas at a flow rate of 10 l / min and using NH ₃ , trimethyl gallium, and trimethyl indium as source gases at 4.0 l / min, respectively. 1 μmol / min and 24 μmol / min were used. The In _0.05 Ga _0.95 N layer has a flow rate of 10 L / min of H ₂ gas as a carrier gas, and 4.0 l / min and 1 μmol / min of NH ₃ , trimethyl gallium, and trimethyl indium as source gases, respectively. Growth was performed using a flow rate of 1.2 μmol / min.

Subsequently, a p-type Al _0.2 Ga _0.8 N single crystal film 28 was grown. The source gas used was NH ₃ , trimethylaluminum, trimethylgallium, and biscyclopentadiethylmagnesium at a flow rate of 4.0 l / min, 10 μmol / min, 24 μmol / min, 3.6 μmol / min, respectively, and a film thickness of 200 nm over 4 minutes. Grown up to. A p-type GaN single crystal film 29 was grown on the p-type Al _0.2 Ga _0.8 N single crystal film 28. The source gas used for the growth is the same as that of the previous n-type GaN single crystal film 22, but instead of SiH ₄ (H ₂ dilution, concentration 10 ppm), biscyclopentadiethyl magnesium is used at a flow rate of 3.6 μmol / min. Used to grow to a film thickness of 100 nm.

Further, a p-type Al _0.15 Ga _0.85 N single crystal film 30 was grown on the p-type GaN single crystal film 29. The source gas used for the growth was n-type Al _0.15 Ga _0.85 N, except that 3.6 μmol / min of biscyclopentadiethyl magnesium was used instead of SiH ₄ (H ₂ dilution, concentration 10 ppm). It was the same as the growth of the crystal film 25, and was grown to a film thickness of 400 nm in 8 minutes. Next, as in the case of the previous p-type GaN single crystal film 29, the p-type GaN single crystal film 31 was grown to a thickness of 500 nm.

After the growth of each single crystal film as described above, the whole was annealed at 700 ° C. in an N ₂ atmosphere. Next, each nitride single crystal film was partially processed by reactive dry etching to expose a part of the lower n-type GaN single crystal layer 22 on the surface. Thereafter, the (10-10) plane of the aluminum nitride single crystal substrate 21 is cleaved to form a resonator, and then on the uppermost p-type GaN single crystal film 31 and the exposed n-type GaN single crystal film 22. Aluminum electrodes 32 and 33 were formed by sputtering to form an LD.

  Samples in the middle of each process were prepared and evaluated using RHEED. All layers were single crystal films having a wurtzite crystal structure, and the (0001) plane of each single crystal film was aluminum nitride. It was found that the single crystal substrate 21 grew parallel to the (0001) plane.

  When the characteristics of the obtained LED were evaluated at room temperature, it was confirmed that laser light having a peak wavelength at 420 nm and a half width of 0.9 nm was emitted. Further, when light was emitted continuously for 1 hour, the temperature of the device did not increase so as to affect the device performance, and performance degradation such as a decrease in luminance did not occur.

[Example 3]
An LD having the structure shown in FIG. 5 was manufactured in the same manner as in Example 2 except that the low-temperature growth buffer layer 23 shown in FIG. 4 was not formed. The LD shown in FIG. 5 has the same structure as that of FIG. 4 in Example 2 except that the low-temperature growth buffer layer 23 does not exist.

  When the characteristics of the LD having the structure of FIG. 5 were evaluated at room temperature, it was confirmed that laser light having a peak wavelength at 420 nm and a half width of 1.0 nm was emitted. Further, although light was emitted continuously for 1 hour, the temperature of the element did not increase so as to affect the element performance, and performance degradation such as a decrease in luminance did not occur. From this result, it was found that even if the low-temperature growth buffer layer was not formed, there was no significant difference in practical performance as compared with the LD of Example 2 in which it was formed.

[Comparative Example 1]
As shown in FIG. 6, the LD was formed in the same manner as in Example 2 except that the sapphire single crystal substrate 41 made of the (0001) plane of sapphire single crystal was used and the resonator was formed by dry etching. went. That is, the LD shown in FIG. 6 has the same structure as the LD of FIG. 4 in Example 2 except that the material of the substrate and the method of forming the resonance surface are different.

  When the characteristics of the LD were evaluated at room temperature, it was confirmed that laser light having a peak wavelength at 420 nm and a half-value width of 1.8 nm was emitted. It was.

[Example 4]
When synthesizing the aluminum nitride single crystal used as the substrate, the same procedure as in Example 1 was conducted except that the SiC single crystal substrate used was a (10-10) plane of 6H—SiC. -10) The surface was synthesized. Using this aluminum nitride (10-10) surface as a substrate and cleaving at the (0001) surface, an LD having the structure shown in FIG. 4 was produced in the same manner as in Example 2.

  When the characteristics of the LD were evaluated at room temperature, light emission of a laser beam having a peak wavelength at 420 nm and a half width of 0.6 nm was obtained. From this result, by using the (10-10) plane on the aluminum nitride single crystal substrate and forming the resonator by cleaving the (0001) plane, it is possible to form an LD with a narrower half-value width of the emission spectrum, and to resonate. It has been found that it is preferable to use the (0001) plane for forming the plane.

[Example 5]
When synthesizing an aluminum nitride single crystal used as a substrate, the SiC single crystal substrate used is a (0001) plane of 6H-SiC, and the growth time of the aluminum nitride single crystal is 50 minutes and 1 hour. In the same manner as in Example 1, (0001) planes of aluminum nitride single crystals were synthesized. Each of the obtained aluminum nitride single crystals has a thickness of 290 μm and 340 μm, respectively, and the half-value width measured by a four-crystal method using a gallium (110) surface by Cu—Kα rays with a rocking curve of the (0002) surface is respectively 1.7 minutes and 1.2 minutes.

  Using the (0001) planes of the aluminum nitride single crystals having different thicknesses as substrates, LDs having the structure shown in FIG. When the characteristics of the obtained LDs were evaluated at room temperature, emission of laser light having a peak wavelength at 420 nm and half-widths of 1.6 nm and 1.5 nm, respectively, was obtained. Further, after emitting light for 24 hours, the half width was measured again to be 1.8 nm and 1.5 nm, respectively.

  From these results, the LD using a substrate (thickness of 290 μm) whose half-width of the rocking curve of the aluminum nitride single crystal substrate exceeds 1.5 minutes has a wide half-width of the emission spectrum and changes with time in the emission characteristics. It was found that the rocking curve half-width of the single crystal substrate is preferably 1.5 minutes or less. It was also found that a single crystal with good crystallinity can be obtained by setting the thickness of the aluminum nitride single crystal substrate to 300 μm or more.

[Example 6]
When synthesizing an aluminum nitride single crystal as a substrate, a mixed powder in which the molar ratio of TiO _{2 to} AlN was changed to 0.001, 0.2, and 10 was used. A (0001) plane of aluminum nitride single crystal was synthesized in the same manner as in Example 1 except that the (0001) plane of 6H—SiC was used and the temperature around the mixed powder was set to 1900 ° C. The content of Ti contained in each obtained single crystal was 8 ppb, 0.06 mol%, and 0.15 mol% of components other than nitrogen, respectively.

  Using the (0001) plane of each aluminum nitride single crystal having a different Ti content as a substrate, LDs having the structure shown in FIG. When the characteristics of each of the obtained LDs were evaluated at room temperature, it was confirmed that each of them had a peak wavelength at 420 nm and had a half-value width of 0.8 nm, 1.0 nm, and 1.9 nm, respectively. Further, after emitting light for 24 hours, the half width was measured again to be 1.5 nm, 1.0 nm, and 1.9 nm, respectively.

  From these results, the LD formed on the aluminum nitride single crystal substrate having a transition metal Ti content of less than 10 ppb shows a change in light emission characteristics over time, and the LD content formed on the substrate exceeds 0.1 mol%. It was found that the formed LD had a tendency that the half width of light emission was widened. From this, it was found that the content of titanium, which is a transition metal in the aluminum nitride single crystal substrate, is preferably 10 ppb or more and 0.1 mol% or less.

[Example 7]
Using the (0001) plane of the same aluminum nitride single crystal as in Example 1 as a substrate, an Al _0.5 Ga _0.5 N pn junction diode having the structure shown in FIG. 7 was formed. That is, as shown in FIG. 7, an n-type Al _0.5 Ga _0.5 N single crystal film 34 is formed on the surface of the aluminum nitride single crystal substrate 21, and then a p-type Al _0.5 is formed thereon. After the Ga _0.5 N single crystal film 35 was formed, electrodes 36 and 37 were provided to constitute a diode.

The growth of each group III-V nitride single crystal film was carried out using the MOCVD method under atmospheric pressure as follows. First, an n-type Al _0.5 Ga _0.5 N single crystal film 34 was grown on the aluminum nitride single crystal substrate 21 at a substrate temperature of 1000 ° C. At that time, H ₂ was used as a carrier gas at a flow rate of 10 l / min, and NH ₃ , trimethylaluminum, trimethylgallium, and SiH ₄ (diluted with H ₂ , concentration 10 ppm) were used as source gases at 4.0 l / min, 10 μmol / min, It was introduced into the reaction chamber at a flow rate of 16 μmol / min and 4 nmol / min, and was grown to a film thickness of 300 nm in 3 minutes.

Next, a p-type Al _0.5 Ga _0.5 N single crystal film 35 was grown while maintaining the substrate temperature at 1000 ° C. At that time, NH ₃ , trimethylaluminum, trimethylgallium, and biscyclopentadiethylmagnesium were used as source gases at a flow rate of 4.0 l / min, 10 μmol / min, 15 μmol / min, and 3.6 nmol / min, respectively, in 4 minutes. The film was grown to a thickness of 320 nm.

After the growth of the single crystal films 34 and 35 as described above, the single crystal films 34 and 35 are partially processed by reactive dry etching to form a lower n-type Al _0.5 Ga _0.5 N. A part of the single crystal film 34 was exposed on the surface. Thereafter, a titanium electrode is formed on the exposed n-type Al _0.5 Ga _0.5 N single crystal film 34 and the uppermost p-type Al _0.5 Ga _0.5 N single crystal film 35 by sputtering. A diode was configured by forming 36 and 37, respectively.

  When the electrical characteristics of the obtained diode were evaluated, good rectification characteristics were obtained at room temperature, and it was confirmed that the diode was operating. Furthermore, as a result of performing a similar operation test with the temperature raised to 200 ° C., rectification characteristics were confirmed, and it was found that the device operates as a diode even at high temperatures. From this, it was found that the aluminum nitride single crystal substrate is also suitable for constituting a diode.

[Comparative Example 2]
As shown in FIG. 8, a diode was fabricated in the same manner as in Example 7 except that a sapphire single crystal substrate 41 made of a (0001) plane of sapphire single crystal was used. That is, the diode shown in FIG. 8 has the same structure as the diode of FIG. 7 in Example 7 except that the material of the substrate is different.

  As a result of evaluating the electrical characteristics of this diode, it was confirmed that the same rectification characteristics were obtained at room temperature, but the same rectification characteristics were confirmed. could not.

It is a schematic sectional drawing which shows the principal part of the semiconductor element of this invention. 1 is a schematic cross-sectional view showing a heating furnace used for manufacturing an aluminum nitride single crystal substrate in Example 1. FIG. 1 is a schematic cross-sectional view showing the structure of a light-emitting diode of Example 1. FIG. 6 is a schematic cross-sectional view showing the structure of a laser diode of Example 2. FIG. 6 is a schematic cross-sectional view showing the structure of a laser diode of Example 3. FIG. 6 is a schematic cross-sectional view showing the structure of a laser diode of Comparative Example 1. FIG. 10 is a schematic cross-sectional view showing the structure of a diode of Example 7. FIG. 6 is a schematic cross-sectional view showing a structure of a diode of Comparative Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aluminum nitride single crystal substrate 2 III-V nitride single crystal film 3 Heating furnace 4 Induction heating coil 5 Heat insulation material muffle 6 Graphite crucible 7 BN crucible 9 Mixed powder 10 Substrate 11 Aluminum nitride single crystal substrate 12 n-type GaN single crystal Film 13 n-type GaN low-temperature growth buffer layer 14 n-type In _0.1 Ga _0.9 N single crystal film 15 p-type GaN single crystal film 16, 17 electrode 21 aluminum nitride single crystal substrate 22 n-type GaN single crystal film 23 n N-type In _0.1 Ga _0.9 N single crystal film 25 n-type Al _0.15 Ga _0.85 N single crystal film 26 n-type GaN single crystal film 27 In _0.2 Ga _{0 .8} N / In _0.05 Ga _0.95 N quantum well structure 28 p-type Al _0.2 Ga _0.8 N single crystal film 29 p-type GaN single crystal film 30 p-type Al _0.15 Ga _0.8 N single crystal film 31 p-type GaN single crystal films 32 and 33 electrode 34 n-type Al _0.5 Ga _0.5 N single crystal film 35 p-type Al _0.5 Ga _0.5 N single crystal film 36, 36 electrode 41 Sapphire single crystal substrate

Claims (4)

  A group III nitride single crystal substrate containing a transition metal of 10 ppb or more and 0.1 mol% or less, and gallium nitride, aluminum nitride, boron nitride, indium nitride, and these materials directly formed on the single crystal substrate A semiconductor device comprising at least one group III-V nitride single crystal film selected from mixed crystals, wherein a transition metal or a precipitate of the nitride or oxide thereof is present in the single crystal substrate. A semiconductor element characterized in that there is no or a precipitate thereof does not affect the characteristics of the semiconductor element formed on the single crystal substrate.   The semiconductor device according to claim 1, wherein an aluminum nitride substrate is used as the group III nitride single crystal substrate.   An aluminum nitride single crystal substrate containing 10 ppb or more and 0.1 mol% or less of a transition metal and having no precipitation of the transition metal or its nitride or oxide, and gallium nitride and nitride formed directly on the single crystal substrate A single crystal film of at least one group III-V nitride selected from aluminum, boron nitride, indium nitride, and mixed crystals made of these materials, and silicon, tin in part of the single crystal film At least one of oxygen, sulfur, selenium and tellurium is intentionally added to give n-type conductivity, or at least one of zinc, beryllium, magnesium and potassium is intentionally added to form p-type A semiconductor element characterized by having conductivity. An aluminum nitride single crystal substrate containing 10 ppb or more and 0.1 mol% or less of a transition metal and having no precipitation of the transition metal or its nitride or oxide, and gallium nitride and nitride formed directly on the single crystal substrate A single crystal film of at least one group III-V nitride selected from aluminum, boron nitride, indium nitride, and mixed crystals made of these materials, and the length and width of the single crystal substrate are both A semiconductor element having a thickness of 10 mm or more and a thickness of 300 μm or more.

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