Abstract: An epitaxial substrate, in which a group of group-III nitride layers is formed on a single-crystal silicon substrate so that a crystal plane is approximately parallel to a substrate surface, comprises: a first group-III nitride layer formed of AlN on the base substrate; a second group-III nitride layer formed of InxxAlyyGazzN (xx+yy+zz=1, 0?xx?1, 0<yy?1 and 0<zz?1) on the first group-III nitride layer; and at least one third group-III nitride layer epitaxially-formed on the second group-III nitride layer, wherein: the first group-III nitride layer is a layer containing multiple defects including at least one type of a columnar crystal, a granular crystal, a columnar domain and a granular domain; and an interface between the first group-III nitride layer and the second group-III nitride layer is a three-dimensional asperity surface.

Abstract: A buffer layer formed of Inx1Aly1Gaz1N formed on a base, with an upper part of the buffer layer containing columnar polycrystalline including a grain boundary existing in a direction substantially perpendicular to a surface of the base. The number of grain boundaries in the lower part of the buffer layer is greater than that in the upper part, and a full width at half maximum of an X-ray rocking curve of the upper part is 300-3000 seconds, RMS of the surface of the buffer layer is 0.2 nm-6 nm, and the ratio of the grain boundary width of the crystal grain of the upper part in a direction parallel to the base surface to the formation thickness of the buffer layer is 0.5-1.5.

Abstract: Provided is an epitaxial substrate for semiconductor device that is capable of achieving a semiconductor device having high reliability in reverse characteristics of schottky junction. An epitaxial substrate for semiconductor device obtained by forming, on a base substrate, a group of group III nitride layers by lamination such that a (0001) crystal plane of each layer is approximately parallel to a substrate surface includes: a channel layer formed of a first group III nitride having a composition of Inx1Aly1Gaz1N (x1+y1+z1=1, z1>0); and a barrier layer formed of a second group III nitride having a composition of Inx2Aly2N (x2+y2=1, x2>0, y2>0), wherein the second group III nitride is a short-range-ordered mixed crystal having a short-range order parameter ? satisfying a range where 0???1.

Abstract: Provided is an epitaxial substrate capable of achieving a semiconductor device that has excellent ohmic contact characteristics as well as satisfactory device characteristics. On a base substrate, a channel layer formed of a first group III nitride that contains at least Al and Ga and has a composition of Inx1Aly1Gaz1N (x1+y1+z1=1) is formed. On the channel layer, a barrier layer formed of a second group III nitride that contains at least In and Al and has a composition of Inx2Aly2Gaz2N (x2+y2+z2=1) is formed such that an In composition ratio of a near-surface portion is larger than an In composition ratio of a portion other than the near-surface portion.

Abstract: Provided is an epitaxial substrate capable of achieving a semiconductor device that has excellent schottky contact characteristics as well as satisfactory device characteristics. On a base substrate, a channel layer formed of a first group III nitride that contains at least Al and Ga and has a composition of Inx1Aly1Gaz1N (x1+y1+z1=1) is formed. On the channel layer, a barrier layer formed of a second group III nitride that contains at least In and Al and has a composition of Inx2Aly2Gaz2N (x2+y2+z2=1) is formed such that an In composition ratio of a near-surface portion is smaller than an In composition ratio of a portion other than the near-surface portion.

Abstract: Provided is an epitaxial substrate capable of manufacturing a HEMT device that has excellent two-dimensional electron gas characteristics and is capable of performing normally-off operation. A channel layer is formed of a first group III nitride represented by Inx1Aly1Gaz1N (x1+y1+z1=1) so as to have a composition in a range determined by x1=0 and 0?y1?0.3. A barrier layer is formed of a second group III nitride represented by Inx2Aly2Gaz2N (x2+y2+z2=1) so as to have a composition, in a ternary phase diagram with InN, AlN and GaN being vertices, in a range surrounded by four straight lines determined in accordance with the composition (AlN molar fraction) of the first group III nitride and to have a thickness of 5 nm or less.

Abstract: Provided is an epitaxial substrate having excellent two-dimensional electron gas characteristics and reduced internal stress due to strains. A channel layer is formed of a first group III nitride represented by Inx1Aly1Gaz1N (x1+y1+z1=1) so as to have a composition in a range determined by x1=0 and 0?y1?0.3. A barrier layer is formed of a second group III nitride represented by Inx2Aly2Gaz2N (x2+y2+z2=1) so as to have a composition, in a ternary phase diagram with InN, AlN and GaN being vertices, in a range surrounded by five straight lines determined in accordance with the composition (AlN molar fraction) of the first group III nitride.

Abstract: An epitaxial substrate including a single-crystal base material and an upper layer of a group III nitride crystal film which is epitaxially formed on a main surface of the base material undergoes heating treatment in a nitrogen atmosphere at 1950° C. or higher for one minute. The result showed that, while a ?-ALON layer was formed only at the interface between the base material and the upper layer, the dislocation density in the group III nitride crystal was reduced to one tenth or less of the dislocation density before the heating treatment. The result also showed that the surface of the epitaxial substrate after the heating treatment had a reduced number of pits, which confirmed that high-temperature and short-time heating treatment was effective at improving the crystal quality and surface flatness of the group III nitride crystal.

Abstract: A method for preparing an AlGaN crystal layer with good surface flatness is provided. A surface layer of AlN is epitaxially formed on a c-plane sapphire single crystal base material by MOCVD method, and the resulting laminated body is then heated at a temperature of 1300° C. or higher so that a template substrate applying in-plane compressive stress and having a surface layer flat at a substantially atomic level is obtained. An AlGaN layer is formed on the template substrate at a deposition temperature higher than 1000° C. by an MOCVD method that includes depositing alternating layers of a first unit layer including a Group III nitride represented by the composition formula AlxGa1-xN (0?x?1) and a second unit layer including a Group III nitride represented by the composition formula AlyGa1-yN (0?y?1 and y?x) such that the AlGaN layer has a superlattice structure.

Abstract: An underlying film 2 of a group III nitride is formed on a substrate 1 by vapor phase deposition. The substrate 1 and the underlying film 2 are subjected to heat treatment in the present of hydrogen to remove the underlying film 2 so that the surface of the substrate 1 is roughened. A seed crystal film 4 of a group III nitride single crystal is formed on a surface of a substrate 1A by vapor phase deposition. A group III nitride single crystal 5 is grown on the seed crystal film 4 by flux method.

Abstract: A heating process is performed in a nitrogen atmosphere at a temperature of not less than 1650° C. upon an epitaxial substrate including a single crystal base and an upper layer made of a group-III nitride crystal and epitaxially formed on a main surface of the single crystal base. The result shows that the heating process reduces the number of pits in a top surface to produce the effect of improving the surface flatness of the group-III nitride crystal. The result also shows that the dislocation density in the group-III nitride crystal is reduced to not more than one-half the dislocation density obtained before the heat treatment.

Abstract: A buffer layer formed of Inx1Aly1Gaz1N formed on a base, with an upper part of the buffer layer containing columnar polycrystalline including a grain boundary existing in a direction substantially perpendicular to a surface of the base. The number of grain boundaries in the lower part of the buffer layer is greater than that in the upper part, and a full width at half maximum of an X-ray rocking curve of the upper part is 300-3000 seconds, RMS of the surface of the buffer layer is 0.2 nm-6 nm, and the ratio of the grain boundary width of the crystal grain of the upper part in a direction parallel to the base surface to the formation thickness of the buffer layer is 0.5-1.5.

Abstract: There is provided a method for preparing an AlGaN crystal layer having an excellent surface flatness. A buffer layer effective in stress relaxation is formed on a template substrate having a surface layer that is flat at a substantially atomic level and to which in-plane compressive stress is applied, and an AlGaN layer is formed on the buffer layer, so that an AlGaN layer can be formed that is flat at a substantially atomic level. Particularly when the surface layer of the template substrate includes a first AlN layer, a second AlN layer may be formed thereon at a temperature of 600° C. or lower, while a mixed gas of TMA and TMG is supplied in a TMG/TMA mixing ratio of 3/17 or more to 6/17 or less, so that a buffer layer effective in stress relaxation the can be formed in a preferred manner.

Abstract: An epitaxial substrate 10 including a single-crystal base material 1 and an upper layer 2 of a group III nitride crystal film which is epitaxially formed on a main surface of the base material undergoes heating treatment in a nitrogen atmosphere at 1950° C. or higher for one minute. The result showed that, while a ?-ALON layer was formed only at the interface between the base material 1 and the upper layer 2, the dislocation density in the group III nitride crystal was reduced to one tenth or less of the dislocation density before the heating treatment. The result also showed that the surface of the epitaxial substrate 10 after the heating treatment had a reduced number of pits, which confirmed that high-temperature and short-time heating treatment was effective at improving the crystal quality and surface flatness of the group III nitride crystal.

Abstract: A method for preparing an AlGaN crystal layer with good surface flatness is provided. A surface layer of AlN is epitaxially formed on a c-plane sapphire single crystal base material by MOCVD method, and the resulting laminated body is then heated at a temperature of 1300° C. or higher so that a template substrate applying in-plane compressive stress and having a surface layer flat at a substantially atomic level is obtained. An AlGaN layer is formed on the template substrate at a deposition temperature higher than 1000° C. by an MOCVD method that includes depositing alternating layers of a first unit layer including a Group III nitride represented by the composition formula AlxGa1-xN (0?x?1) and a second unit layer including a Group III nitride represented by the composition formula AlyGa1-yN (0?y?1 and y?x) such that the AlGaN layer has a superlattice structure.

Abstract: There is provided a method for preparing an AlGaN crystal layer having an excellent surface flatness. A buffer layer effective in stress relaxation is formed on a template substrate having a surface layer that is flat at a substantially atomic level and to which in-plane compressive stress is applied, and an AlGaN layer is formed on the buffer layer, so that an AlGaN layer can be formed that is flat at a substantially atomic level. Particularly when the surface layer of the template substrate includes a first AlN layer, a second AlN layer may be formed thereon at a temperature of 600° C. or lower, while a mixed gas of TMA and TMG is supplied in a TMG/TMA mixing ratio of 3/17 or more to 6/17 or less, so that a buffer layer effective in stress relaxation the can be formed in a preferred manner.

Abstract: A substrate for film growth of group III nitride, a method of manufacturing the same, and a semiconductor device using the same are provided which can make an AlN thin film relatively thin without cloudiness, as well as cracks and pits are reduced in a group III nitride thin film layer constituting the device grown thereon. A substrate 10 for film growth of group III nitride is constituted which includes a substrate material 11 and an AlN thin film 12 formed on said substrate as a buffer layer, and a semiconductor device comprising group III nitride thin film is formed thereon, and the AlN thin film is formed at plural steps at least one of which changes film growth conditions during the film growth.

Abstract: A heating process is performed in a nitrogen atmosphere at a temperature of not less than 1650° C. upon an epitaxial substrate including a single crystal base and an upper layer made of a group-III nitride crystal and epitaxially formed on a main surface of the single crystal base. The result shows that the heating process reduces the number of pits in a top surface to produce the effect of improving the surface flatness of the group-III nitride crystal. The result also shows that the dislocation density in the group-III nitride crystal is reduced to not more than one-half the dislocation density obtained before the heat treatment.

Abstract: A substrate for epitaxial growth allowing formation of an Al-containing group III nitride film having high crystal quality is provided. A nitride film containing at least Al is formed on a 6H—SiC base by CVD at a temperature of at least 1100° C., for example. The substrate for epitaxial growth allowing formation of an Al-containing group III nitride film having high crystal quality is obtained by setting the dislocation density of the nitride film to not more than 1×1011/cm2, the full width at half maximum of an X-ray rocking curve for (002) plane to not more than 200 seconds and the full width at the half maximum of the X-ray rocking curve for (102) plane to not more than 1500 seconds.

Abstract: The crystal orientation of the main surface of a sapphire single crystal base material to constitute an epitaxial substrate is inclined from the <0001> orientation (c-axis) preferably for the <1-100> orientation (m-axis) by a range within 0.02-0.3 degrees. Then, a surface nitride layer is formed at the main surface of the base material. Then, a III nitride underfilm is formed on the main surface of the base material via the surface nitride layer. The III nitride underfilm includes at least Al element, and the full width at half maximum at (101-2) reflection in X-ray rocking curve of the III nitride underfilm is 2000 seconds. The surface roughness Ra within 5 ?m area is 3.5 ?.