JP5482682B2 - Group III nitride semiconductor electronic device, epitaxial substrate, and method of fabricating group III nitride semiconductor electronic device - Google Patents

Description

  The present invention relates to a group III nitride semiconductor electronic device, an epitaxial substrate, and a method for manufacturing a group III nitride semiconductor electronic device.

  Non-Patent Document 1 describes a high electron mobility transistor having an AlGaN channel layer. This AlGaN channel layer is grown on a GaN template. The thickness and Al composition of the AlGaN channel layer are 1.0 μm and 0.2, respectively. The thickness and Al composition of the AlGaN barrier layer are 20 nm and 0.4, respectively.

  Non-Patent Document 2 describes a high electron mobility transistor having an AlGaN buffer layer. This buffer layer is grown on an AlN template using SiC. The thickness and Al composition of the AlGaN buffer layer are 550 nm and 0.06, respectively. The thickness and Al composition of the AlGaN cap layer are 25 nm and 0.31, respectively.

  Non-Patent Document 3 describes a high electron mobility transistor having an AlGaN buffer layer. This buffer layer is grown on an AlN template using sapphire. The thickness and Al composition of the AlGaN buffer layer are 600 nm and 0.29, respectively. The thickness and Al composition of the AlGaN channel layer are 25 nm and 0.49, respectively.

  Non-Patent Document 4 discloses a mechanism of current collapse in a hetero field effect transistor (a layer called “virtual gate” is formed on the surface of an AlGaN barrier layer to suppress the flow of two-dimensional electrons) and the like. Non-Patent Document 5 discloses the critical film thickness of an AlGaN film grown on GaN.

Takuma Nanjo, Misaichi Takeuchi1, Muneyoshi Suita, Yuji Abe, Toshiyuki Oishi, Yasunori Tokuda, and Yoshinobu Aoyagi1, “First Operation of AlGaN Channel High Electron Mobility Transistors,” Applied Physics Express 1 (2008) 011101 Ajay RAMAN, Sansaptak DASGUPTA, Siddharth RAJAN, James S. SPECK, and Umesh K. MISHRA, `` AlGaN Channel High Electron Mobility Transistors: Device Performance and Power-Switching Figure of Merit, '' Japanese Journal of Applied Physics Vol. 47, No. 5, 2008, pp. 3359-3361 Hashimoto, Katsushi Akita1, Tatsuya Tanabe1, Hideaki Nakahata1, Kenichiro Takeda, and Hiroshi Amano, ”Study of two-dimensional electron gas in AlGaN channel HEMTs with high crystalline quality Shin,” Phys. Status Solidi C7, No. 7-8, 1938- 1940 (2010) Ramakrishna Vetury, Naiqain Q. Zhang, Stacia Keller, and Umesh K. Mishra, “The Impact of Surface States on the DC and RF Characteristics of AlGaN / GaN HFETs”, IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 48, NO.3, MARCH 2001, 560-566 J. A. Floro, D. M. Follstaedt, P. Provencio, S. J. Hearne, and S. R. Lee, “Misfit dislocation formation in the AlGaN / GaN heterointerface,” JOURNAL OF APPLIED PHYSICS VOLUME 96, NUMBER 12, 1 DECEMBER 2004

  As shown in Non-Patent Document 5, the thickness of an AlGaN film grown on GaN has a limit called a critical thickness. When growing an AlGaN film exceeding the critical thickness, cracks and defects are introduced into the AlGaN film. Therefore, when AlGaN is used, for example, in the barrier layer of a high electron mobility transistor, the maximum thickness possible for the barrier layer is also defined by the critical film thickness. The transistors of Non-Patent Documents 1 to 3 cannot escape from the control of the critical film thickness, and the Al composition and thickness of the barrier layer applied to the transistors in these documents are as follows. The thickness and Al composition of the AlGaN barrier layer in Non-Patent Document 1 are 20 nm and 0.4, respectively. The thickness and Al composition of the AlGaN cap layer in Non-Patent Document 2 are 25 nm and 0.31, respectively. The thickness and Al composition of the AlGaN channel layer in Non-Patent Document 3 are 25 nm and 0.49, respectively.

  According to the knowledge of the inventors, the thickness of the semiconductor layer provided between the channel layer and the gate electrode of the transistor affects its operating characteristics. As shown in Non-Patent Document 4, when a transistor using a nitride semiconductor is operated, the charge layer (virtual gate) on the AlGaN surface prevents the movement of two-dimensional electrons, so that the distance between them is increased. This makes it possible to improve the movement of two-dimensional electrons. Therefore, it is desired to make this semiconductor layer thicker to separate the charge layer on the AlGaN surface and the two-dimensional electrons. For example, in a high electron mobility transistor, this thick semiconductor layer improves resistance to current collapse. In a transistor having a gate recess structure, a thick semiconductor layer improves not only current collapse but also device breakdown voltage. These are examples of the technical contribution of a thick semiconductor layer that separates the gate electrode from the channel layer.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a group III nitride semiconductor electronic device capable of thickening a semiconductor layer separating a gate electrode from a current path in a semiconductor stack. Another object of the present invention is to provide an epitaxial substrate for a group III nitride semiconductor electronic device. It is a further object of the present invention to provide a method for fabricating a group III nitride semiconductor electronic device.

A group III nitride semiconductor electronic device according to the present invention is provided on a semiconductor surface made of (a) Al _X Ga _1-X N (0 <X ≦ 1), and is made of a first group III nitride semiconductor material. (B) a second semiconductor layer made of a second group III nitride semiconductor material having a larger band gap than the band gap of the first group III nitride semiconductor material; And a gate electrode provided on the second semiconductor layer. The second semiconductor layer is provided on the first semiconductor layer, the first group III nitride semiconductor material is different from the Al _X Ga _1-X N, and the first semiconductor layer is distorted. Enclose. The thickness of the second semiconductor layer is larger than the critical film thickness defined by the composition of the unstrained first group III nitride semiconductor material and the composition of the second group III nitride semiconductor material. It is also possible.

According to the above group III nitride semiconductor electronic device, the first semiconductor layer contains strain. Further, the second semiconductor layer has a thickness larger than a critical film thickness defined by the composition of the first group III nitride semiconductor material without distortion and the composition of the second group III nitride semiconductor material. Make it possible. At this time, the first semiconductor layer is not lattice-matched to the underlying Al _X Ga _1-X N semiconductor, and the actual lattice constant of the first semiconductor layer in the group III nitride semiconductor electronic device (for example, The lattice constant in the a-axis direction) is different from the lattice constant of the underlying Al _X Ga _1-X N semiconductor (for example, the lattice constant in the a-axis direction). In addition, since the first semiconductor layer includes strain, the actual lattice constant (for example, lattice constant in the a-axis direction) of the first semiconductor layer in the group III nitride semiconductor electronic device is not strained. It is different from the lattice constant inherent to the group nitride semiconductor material (for example, the lattice constant in the a-axis direction, a0). That is, the actual lattice constant of the first semiconductor layer in the group III nitride semiconductor electronic device has a value between these lattice constants.

Since the second semiconductor layer is provided on the first semiconductor layer including the strain in this way, the thickness of the second semiconductor is the second semiconductor layer on the first semiconductor layer in the conventional case of no strain. The thickness exceeding the critical thickness when the layer is provided can be achieved.
Further, even when the second semiconductor layer does not exceed the conventional critical thickness, the strain applied to the second semiconductor layer is reduced as compared with the conventional one, and good crystal quality can be obtained.

A group III nitride semiconductor electronic device according to the present invention is provided on a semiconductor surface made of (a) Al _X Ga _1-X N (0 <X ≦ 1), and is made of a first group III nitride semiconductor material. (B) a second semiconductor layer made of a second group III nitride semiconductor material having a larger band gap than the band gap of the first group III nitride semiconductor material; And a gate electrode provided on the second semiconductor layer. The second semiconductor layer is provided on the first semiconductor layer, the first group III nitride semiconductor material is different from the Al _X Ga _1-X N, and the first semiconductor layer is strained And lattice relaxation on Al _X Ga _1-X N on the semiconductor surface.

According to the above group III nitride semiconductor electronic device, the first semiconductor layer is lattice-relaxed on Al _X Ga _1-X N on the semiconductor surface. Therefore, the first semiconductor layer is not lattice matched to the underlying Al _X Ga _1-X N semiconductor, and the actual lattice constant of the first semiconductor layer in the group III nitride semiconductor electronic device (eg, a The lattice constant in the axial direction is different from the lattice constant of the underlying Al _X Ga _1-X N semiconductor (for example, the lattice constant in the a-axis direction). In addition, since the first semiconductor layer includes strain, it is not completely lattice-relaxed, and the actual lattice constant of the first semiconductor layer in the group III nitride semiconductor electronic device (for example, the lattice constant in the a-axis direction) Is different from the lattice constant inherent to the unstrained first group III nitride semiconductor material (for example, the lattice constant in the a-axis direction, a0). That is, the actual lattice constant of the first semiconductor layer in the group III nitride semiconductor electronic device has a value between these lattice constants.

Since the second semiconductor layer is provided on the first semiconductor layer, the critical film thickness of the second semiconductor layer is defined by the lattice constant of the first semiconductor layer and the lattice constant of the second semiconductor layer. The The critical film thickness of the second semiconductor layer is independent of the lattice constant of the underlying Al _X Ga _1-X N semiconductor.

The group III nitride semiconductor electronic device according to the present invention may further include a support base on which the first and second semiconductor layers are mounted. The support base may have the semiconductor surface, and the support base may be made of the Al _X Ga _1-X N. According to the group III nitride semiconductor electronic device, the semiconductor stack for the group III nitride semiconductor electronic device can be provided on the Al _X Ga _1-X N supporting base.

The group III nitride semiconductor electronic device according to the present invention may further include a support base on which the first and second semiconductor layers are mounted. The support base includes a group III nitride layer providing the semiconductor surface and a support made of a material different from the Al _X Ga _1-X N, and the group III nitride layer is formed on the support. Can be mounted. In the group III nitride semiconductor electronic device, Si substrate, a sapphire substrate, SiC substrate, a semiconductor for the group III nitride semiconductor electronic device on other Al X _Ga 1-X _N template provided on a substrate A stack can be provided.

An epitaxial substrate for a group III nitride semiconductor electronic device according to the present invention comprises (a) a substrate having a semiconductor surface made of Al _X Ga _1-X N (0 <X ≦ 1), and (b) the semiconductor surface. A first semiconductor layer for the channel layer, and (c) a band gap larger than the band gap of the first group III nitride semiconductor material And a second semiconductor layer for the barrier layer. The second semiconductor layer is provided on the first semiconductor layer, the first group III nitride semiconductor material is different from the Al _X Ga _1-X N, and the first semiconductor layer is distorted. Enclose. The thickness of the second semiconductor layer is larger than a critical film thickness defined by the composition of the second group III nitride semiconductor material and the composition of the unstrained first group III nitride semiconductor material. It is also possible to do.

The epitaxial substrate includes a semiconductor stack provided on the substrate, and the semiconductor stack includes the first and second semiconductor layers. The semiconductor stack has a main surface provided so that a gate electrode can be mounted. In this semiconductor stack, the first semiconductor layer contains strain, but is defined by the composition of the unstrained first group III nitride semiconductor material and the composition of the second group III nitride semiconductor material. The second semiconductor layer can have a thickness greater than the critical thickness. In this semiconductor stack, the first semiconductor layer is not lattice-matched to the underlying Al _X Ga _1-X N semiconductor, and the actual lattice constant of the first semiconductor layer in the epitaxial substrate (for example, in the a-axis direction) Is different from the lattice constant of the underlying Al _X Ga _1-X N semiconductor (for example, the lattice constant in the a-axis direction). In addition, since the first semiconductor layer contains strain, the actual lattice constant (for example, lattice constant in the a-axis direction) of the first semiconductor layer in the epitaxial substrate is the unstrained first group III nitride semiconductor material. Is different from the inherent lattice constant (for example, the lattice constant in the a-axis direction, a0). That is, the actual lattice constant of the first semiconductor layer in the group III nitride semiconductor electronic device has a value between these lattice constants.

Since the second semiconductor layer is provided on the first semiconductor layer, the lattice constant that defines the critical film thickness of the second semiconductor layer is not the lattice constant of the underlying Al _X Ga _1-X N semiconductor. , Determined only by the actual lattice constant of the first semiconductor layer and the lattice constant of the second semiconductor layer. The critical film thickness of the second semiconductor layer is independent of the lattice constant of the underlying Al _X Ga _1-X N semiconductor.

An epitaxial substrate for a group III nitride semiconductor electronic device according to the present invention includes (a) a substrate having a semiconductor surface made of Al _X Ga _1-X N (0 <X ≦ 1), and (b) Al _X Ga. _{A first} semiconductor layer provided on a semiconductor surface of _1- XN (0 <X ≦ 1), made of a first group III nitride semiconductor material, for a channel layer; and (c) the first A second group III nitride semiconductor material having a larger band gap than that of the first group III nitride semiconductor material, and a second semiconductor layer for the barrier layer. The second semiconductor layer is provided on the first semiconductor layer, the first group III nitride semiconductor material is different from the Al _X Ga _1-X N, and the first semiconductor layer is strained And lattice relaxation on Al _X Ga _1-X N on the semiconductor surface.

  The epitaxial substrate includes a semiconductor stack provided on the substrate, and the semiconductor stack includes the first and second semiconductor layers. The semiconductor stack has a main surface provided so that a gate electrode can be mounted.

In this semiconductor stack, the first semiconductor layer is lattice-relaxed on Al _X Ga _1-X N on the semiconductor surface. Therefore, the first semiconductor layer is not lattice-matched to the underlying Al _X Ga _1-X N semiconductor, and the actual lattice constant of the first semiconductor layer in the epitaxial substrate (for example, the lattice constant in the a-axis direction) ) Is different from the lattice constant (for example, lattice constant in the a-axis direction) of the base Al _X Ga _1-X N semiconductor. In addition, since the first semiconductor layer includes strain, it is not completely lattice-relaxed and is in a lattice-relaxed state, and the actual lattice constant of the first semiconductor layer in the epitaxial substrate (for example, the a-axis direction) Is different from the lattice constant inherent to the unstrained first group III nitride semiconductor material (for example, the lattice constant in the a-axis direction, a0). That is, the actual lattice constant of the first semiconductor layer in the group III nitride semiconductor electronic device has a value between these lattice constants.

Since the second semiconductor layer is provided on the first semiconductor layer, the lattice constant that defines the critical film thickness of the second semiconductor layer is not the lattice constant of the underlying Al _X Ga _1-X N semiconductor. And the lattice constant of the first semiconductor layer. The critical film thickness of the second semiconductor layer is independent of the lattice constant of the underlying Al _X Ga _1-X N semiconductor.

The present invention relates to a method for fabricating a group III nitride semiconductor electronic device. This method includes (a) growing a first semiconductor layer made of a first group III nitride semiconductor material on a semiconductor surface made of Al _X Ga _1-X N (0 <X ≦ 1). (B) growing a second semiconductor layer on the first semiconductor layer, and (c) forming a gate electrode after growing the second semiconductor layer. The first group III nitride semiconductor material is different from the Al _X Ga _1-X N, and the second semiconductor layer has a second band gap larger than the band gap of the first group III nitride semiconductor material. And the first semiconductor layer contains strain. The thickness of the second semiconductor layer may be larger than the critical film thickness defined by the composition of the unstrained first group III nitride semiconductor material and the composition of the second group III nitride semiconductor material. Is possible.

According to the above manufacturing method, the second film thickness greater than the critical film thickness defined by the composition of the unstrained first group III nitride semiconductor material and the composition of the second group III nitride semiconductor material. And growing a first semiconductor layer including a strain and including a strain. Therefore, the first semiconductor layer is not lattice matched to the underlying Al _X Ga _1-X N semiconductor, and the actual lattice constant of the first semiconductor layer in the group III nitride semiconductor electronic device (eg, a The lattice constant in the axial direction is different from the lattice constant of the underlying Al _X Ga _1-X N semiconductor (for example, the lattice constant in the a-axis direction). In addition, since the first semiconductor layer includes strain, the actual lattice constant (for example, lattice constant in the a-axis direction) of the first semiconductor layer in the group III nitride semiconductor electronic device is not strained. It is different from a lattice constant (for example, lattice constant in the a-axis direction, a0) inherent to the group nitride semiconductor material. That is, the actual lattice constant of the first semiconductor layer in the group III nitride semiconductor electronic device has a value between these lattice constants.

Next, a second semiconductor layer is grown on the first semiconductor layer. Therefore, the lattice constant that defines the critical film thickness of the second semiconductor layer is not the lattice constant of the underlying Al _X Ga _1-X N semiconductor, but the lattice constant of the first semiconductor layer. The critical film thickness of the second semiconductor layer is independent of the lattice constant of the underlying Al _X Ga _1-X N semiconductor.

In the above embodiment according to the present invention, the first semiconductor layer contains a strain.
Said second semiconductor layer comprises _{Al Z Ga 1-Z N (} 0 <Z ≦ 1, Z ≦ X), said first semiconductor layer is _{Al Y Ga 1-Y N (} 0 ≦ Y <1, Y <Z, Y <X), and the thickness of the Al _Z Ga _1-Z N of the second semiconductor layer is more than the critical thickness defined by the Al _Y Ga _1-Y N in the case of no strain. Can be bigger. This invention can provide a thick _{Al Z Ga 1-Z} N to the second semiconductor layer for barrier layers.

In the above embodiment according to the present invention (group III nitride semiconductor electronic device, epitaxial substrate, and method of manufacturing group III nitride semiconductor electronic device), the first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X), the second semiconductor layer is made of Al _Z Ga _1-Z N (0 <Z ≦ 1, Z ≦ X), and the Al _Z Ga ₁₋ aluminum composition of _Z N is greater than the aluminum composition of the _{Al Y Ga 1-Y} N, the _{Al Y Ga 1-Y} aluminum composition of N is aluminum composition smaller than the _{Al X Ga 1-X} N.

In the present invention, the first semiconductor layer is made of GaN or AlGaN, and the second semiconductor layer is made of AlGaN larger than the Al composition of the first semiconductor layer. The actual lattice constant (lattice constant in a strained state) in the first semiconductor layer is the difference between the lattice constant of the underlying Al _X Ga _1-X N and the lattice constant of unstrained Al _Y Ga _1-Y N. Since the second semiconductor layer is provided on the first semiconductor layer having the intermediate lattice constant and the intermediate lattice constant, the critical film thickness of the second semiconductor layer is defined based on the intermediate lattice constant. The The critical film thickness of Al _Z Ga _1-Z N in the second semiconductor layer is larger than the critical film thickness based on the lattice constant inherent to Al _Y Ga _1-Y N (lattice constant in the case of no strain). Become.

In the above aspect of the present invention, the channel layer of the group III nitride semiconductor electronic device includes the first semiconductor layer, and the barrier layer of the group III nitride semiconductor electronic device includes the second semiconductor layer. The first semiconductor layer is made of ternary AlGaN, the second semiconductor layer is made of ternary AlGaN, and the AlGaN of the first semiconductor layer is bonded to Al _X Ga _1-X N of the semiconductor main surface. Can be made.

  In the present invention, an AlGaN / AlGaN heterojunction is provided for a group III nitride semiconductor electronic device. A two-dimensional electron gas layer is formed at the heterojunction. This electron gas is controlled by the electric field from the gate electrode through the AlGaN barrier layer. III-nitride semiconductor electronic devices can receive technical contributions due to thick AlGaN barrier layers.

In the above aspect of the present invention, the channel layer of the group III nitride semiconductor electronic device includes the first semiconductor layer, and the barrier layer of the group III nitride semiconductor electronic device includes the second semiconductor layer. The first semiconductor layer is made of binary GaN, the second semiconductor layer is made of ternary AlGaN, and the GaN of the first semiconductor layer is bonded to Al _X Ga _1-X N of the semiconductor main surface. Can be made.

  In the present invention, an AlGaN / GaN heterojunction is provided for a group III nitride semiconductor electronic device. A two-dimensional electron gas layer is formed at the heterojunction. This electron gas is controlled by the electric field from the gate electrode through the AlGaN barrier layer. III-nitride semiconductor electronic devices can receive technical contributions from thick AlGaN barrier layers.

  In the above aspect of the invention, the first semiconductor layer forms a heterojunction with the second semiconductor layer, and the second semiconductor layer is provided coherently on the first semiconductor layer. It is preferable that

  According to the present invention, since the second semiconductor layer is provided on the first semiconductor layer coherently, the second semiconductor layer is not relaxed (relative to the first semiconductor layer). The lattice constant of the second semiconductor layer (for example, the lattice constant in the a-axis direction) is substantially equal to the lattice constant of the first semiconductor layer (for example, the lattice constant in the a-axis direction). Dislocations are not introduced into the above heterojunction.

In the above aspect of the invention, the first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X), and the first semiconductor layer is lattice-relaxed. has a rate R, the lattice relaxation rate R _{(d (Al Y Ga 1-} Y N) -d (Al X Ga 1-X N)) / (d0 (Al Y Ga 1-Y N) - defined by _{d0 (Al X Ga 1-X} N)). The lattice relaxation rate R is preferably greater than zero and not greater than 0.9. The first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X), and the lattice relaxation rate R is larger than zero and 0.8 or less. It is preferable.
Note that, _d0 (Al _{Y Ga 1-Y} N) are the a-axis lattice constant of the _Al Y _{Ga 1-Y} N when _{unstrained, d0 (Al X Ga 1-} X N) is unstrained Is the a-axis lattice constant of Al _X Ga _1-X N.
d (Al _Y Ga _1-Y N) is the lattice constant of Al _Y Ga _1-Y N in the case of having actual strain or the like. Note that d (Al _X Ga _1-X N) is an a-axis lattice constant of actual Al _X Ga _1-X N, but since it is usually used for the underlying layer, d0 (Al _X It becomes almost the same value as Ga _1−X N).

In the embodiment according to the present invention, it is preferable that the Al _X Ga _1-X N is AlN. In the present invention, low dislocation AlN can be used as a support substrate. For example, AlN that can lower the threading dislocation density can be used as the underlying semiconductor region.

In the above aspect of the present invention, it is preferable that the semiconductor surface of the Al _X Ga _1-X N has a c-plane. The present invention utilizes c-plane sliding in the first semiconductor layer to release internal strain. When the c-plane is a smooth surface, defects based on lattice mismatch do not propagate in the direction of the surface of the first semiconductor layer. Therefore, the heterojunction between the first semiconductor layer and the second semiconductor layer is not directly affected by defects due to the release of internal strain.

In the above aspect of the invention, the first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X), and the second semiconductor layer is made of Al 2 _{Z 3.} Ga ₁ -ZN (0 <Z ≦ 1, Z ≦ X), and the difference in aluminum composition between the second semiconductor layer and the first semiconductor layer is 0.17 or more, and the second The thickness of the semiconductor layer is preferably larger than 140 nm. In the above aspect of the invention, the first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X), and the second semiconductor layer is Al _Z Ga _1-Z N (0 <Z ≦ 1, Z ≦ X), a difference in aluminum composition between the second semiconductor layer and the first semiconductor layer is 0.22 or more, and the first The thickness of the semiconductor layer 2 is preferably larger than 92 nm. Furthermore, in the above aspect of the present invention, the first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X), and the second semiconductor layer is Al _Z Ga _1-Z N (0 <Z ≦ 1, Z ≦ X), a difference in aluminum composition between the second semiconductor layer and the first semiconductor layer is 0.37 or more, The thickness of the semiconductor layer 2 is preferably larger than 30 nm.

In the manufacturing method according to the present invention, the first group III nitride semiconductor material is different from the Al _X Ga _1-X N, and the second semiconductor layer is a band gap of the first group III nitride semiconductor material. It is made of a second group III nitride semiconductor material having a larger band gap, and the first semiconductor layer contains strain. The thickness of the second semiconductor layer is larger than the critical film thickness defined by the composition of the unstrained first group III nitride semiconductor material and the composition of the second group III nitride semiconductor material. Is possible.

In the manufacturing method according to the present invention, the first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X), and the second semiconductor layer is made of Al _Z Ga. _1-ZN (0 <Z ≦ 1, Z ≦ X), and the aluminum composition of the Al _Z Ga _1-Z N is larger than the aluminum composition of the Al _Y Ga _1-Y N, and the Al _Y Ga ₁₋ aluminum composition of _Y N is smaller than the aluminum composition of the _{Al X Ga 1-X} N.

According to this manufacturing method, the first semiconductor layer is made of GaN or AlGaN, and the second semiconductor layer is made of AlGaN larger than the Al composition of the first semiconductor layer. The actual lattice constant (lattice constant in a strained state) in the first semiconductor layer is the difference between the lattice constant of the underlying Al _X Ga _1-X N and the lattice constant of unstrained Al _Y Ga _1-Y N. Since the second semiconductor layer is provided on the first semiconductor layer having the intermediate value and the intermediate lattice constant, the critical film thickness of the second semiconductor layer is defined based on the intermediate lattice constant. . The critical film thickness of Al _Z Ga _1-Z N in the second semiconductor layer is larger than the critical film thickness based on the lattice constant inherent to Al _Y Ga _1-Y N.

  As described above, according to the present invention, there is provided a group III nitride semiconductor electronic device capable of increasing the thickness of the semiconductor layer separating the gate electrode from the current path in the semiconductor stack. The present invention also provides an epitaxial substrate for a group III nitride semiconductor electronic device. Furthermore, according to the present invention, a method for fabricating a group III nitride semiconductor electronic device is provided.

FIG. 1 is a drawing schematically showing a group III nitride semiconductor electronic device and an epitaxial substrate according to the present embodiment. FIG. 2 is a drawing showing the relationship between the lattice constants of the first semiconductor layer, the second semiconductor layer, and the support substrate. FIG. 3 is a drawing showing an example of a reciprocal lattice mapping image of an epitaxial substrate created in an experiment. FIG. 4 is a diagram showing a list of results of experiments in the examples. FIG. 5 is a drawing showing the relationship between the Al composition difference between the channel layer and the barrier layer and the critical film thickness of the barrier layer. FIG. 6 is a drawing showing a main process flow in the method of manufacturing a group III nitride semiconductor electronic device according to the present embodiment.

  Subsequently, an embodiment relating to a group III nitride semiconductor electronic device, an epitaxial substrate, and an epitaxial substrate and a group III nitride semiconductor electronic device of the present invention will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

FIG. 1 is a drawing schematically showing a group III nitride semiconductor electronic device and an epitaxial substrate according to the present embodiment. The group III nitride semiconductor electronic device 11 includes a first semiconductor layer 13, a second semiconductor layer 15, and a gate electrode 17. The semiconductor stack 19 includes a first semiconductor layer 13 and a second semiconductor layer 15. The semiconductor stacked layer 19 can have a main surface 19a provided so that the gate electrode 17 can be bonded. The second semiconductor layer 15 is provided on the first semiconductor layer 13. The gate electrode 17 is provided on the second semiconductor layer 15. The first semiconductor layer 13 is made of a first group III nitride semiconductor material, and the first group III nitride semiconductor material can be, for example, AlGaN, GaN, or the like. The first semiconductor layer 13 is provided on the semiconductor surface 21 a made of Al _X Ga _1-X N (0 <X ≦ 1). The second semiconductor layer 15 is made of a second group III nitride semiconductor material, and the second group III nitride semiconductor material can be, for example, AlGaN. As shown in part (b) of FIG. 1, the band gap E15 of the second group III nitride semiconductor material is larger than the band gap E13 of the first group III nitride semiconductor material. The first group III nitride semiconductor material of the first semiconductor layer 13 is different from Al _X Ga _1-X N, and the first semiconductor layer 13 contains strain. Further, the thickness T15 of the second semiconductor layer 15 can be larger than the critical film thickness defined by the composition of the unstrained first group III nitride semiconductor material.

In this group III nitride semiconductor electronic device 11, since the first semiconductor layer 13 includes strain, the strained first group III nitride semiconductor of the first semiconductor layer 13 in the group III nitride semiconductor electronic device 11. The lattice constant d (13) of the material (for example, the lattice constant in the a-axis direction) is different from the lattice constant d0 (13) (for example, the lattice constant in the a-axis direction) of the unstrained first group III nitride semiconductor material. The second semiconductor layer 15 has a thickness larger than the critical film thickness defined by the composition of the unstrained first group III nitride semiconductor material. Therefore, the first semiconductor layer 13 is not lattice-matched to the underlying Al _X Ga _1-X N semiconductor, and the first semiconductor layer 13 has a distorted first group III nitride semiconductor material lattice. The constant d (13) (for example, the lattice constant in the a-axis direction) is different from the lattice constant d (21) (for example, the lattice constant in the a-axis direction) of the base Al _X Ga _1-X N semiconductor.

  That is, the lattice constant d (13) of the distorted first group III nitride semiconductor material of the first semiconductor layer 13 in the group III nitride semiconductor electronic device 11 is the lattice constant d (21) and the lattice constant d0 (13). ) Between.

Since the second semiconductor layer 15 is provided on the first semiconductor layer 13, the lattice constant that defines the critical film thickness of the second semiconductor layer 15 is the lattice constant of the Al _X Ga _1-X N semiconductor. Instead, the lattice constant d (13) of the first semiconductor layer 13 is obtained. The critical film thickness of the second semiconductor layer 15 is independent of the lattice constant of the underlying Al _X Ga _1-X N semiconductor.

Further, in the group III nitride semiconductor electronic device 11, the first semiconductor layer 13 includes strain and is lattice-relaxed on Al _X Ga _1-X N on the semiconductor surface 21a.

In the group III nitride semiconductor electronic device 11, when the first semiconductor layer 13 is lattice-relaxed on the Al _X Ga _1-X N of the semiconductor surface 21 a, the first semiconductor layer 13 is the underlying Al The lattice constant d (13) of the distorted first group III nitride semiconductor material of the first semiconductor layer 13 in the group III nitride semiconductor electronic device 11 is not lattice matched to the _X Ga _1-X N semiconductor. ) (For example, the lattice constant in the a-axis direction) is different from the lattice constant d (21) (for example, the lattice constant in the a-axis direction) of the base Al _X Ga _1-X N semiconductor. In addition, since the first semiconductor layer 13 includes strain, it is not completely lattice-relaxed and is in a lattice-relaxed state, and the first semiconductor layer 13 in the group III nitride semiconductor electronic device 11 is strained. However, the lattice constant d (13) of the first group III nitride semiconductor material (for example, the lattice constant in the a-axis direction) is the lattice constant d0 (13) (inherent to the unstrained first group III nitride semiconductor material). For example, it is different from the lattice constant in the a-axis direction). That is, the lattice constant d (13) has a value between the lattice constant d (21) and the lattice constant d0 (13).

Since the second semiconductor layer 15 is provided on the lattice-relaxed first semiconductor layer 13, the lattice constant that defines the critical film thickness of the second semiconductor layer 15 is the lattice constant d of the first semiconductor layer 13. (13) The critical film thickness of the second semiconductor layer 15 is independent of the lattice constant of the underlying Al _X Ga _1-X N semiconductor.

The group III nitride semiconductor electronic device 11 can thicken the semiconductor layer 15 that separates the gate electrode 17 from the current path in the semiconductor stack 19 in two cases as follows: the first semiconductor layer 13 contains strain At the same time, the second semiconductor layer 15 has a thickness T15 larger than the critical film thickness defined by the composition of the unstrained first group III nitride semiconductor material; the first semiconductor layer 13 contains the strain. At the same time, the lattice is relaxed with respect to Al _X Ga _1-X N on the semiconductor surface 21a.

  The second semiconductor layer 15 is provided on the first semiconductor layer 13 in a coherent manner. Therefore, the second semiconductor layer 15 is not relaxed. The lattice constant d (15) of the second semiconductor layer 15 (for example, the lattice constant in the a-axis direction) is substantially equal to the lattice constant d (13) of the first semiconductor layer 13 (for example, the lattice constant in the a-axis direction). . The first semiconductor layer 13 forms a heterojunction 27a with the second semiconductor layer 15, and no dislocation is introduced into the heterojunction 27a.

The group III nitride semiconductor electronic device 11 can further include a support base 21 on which the first and second semiconductor layers 13 and 15 are mounted. The support base 21 has a semiconductor surface 21a, and the semiconductor surface 21a extends in the X-axis direction and the Y-axis direction of the coordinate system S. The first and second semiconductor layers 13 and 15 are arranged in the normal direction (Z-axis direction) of the semiconductor surface 21 a of the support base 21. In the present embodiment, the first semiconductor layer 13 forms a junction 27b with Al _X Ga _1-X N on the semiconductor surface 21a. Substrate 21, as shown in (c) portion of FIG. _1, may consist of Al _{X Ga 1-X} N. A semiconductor stack 19 for the group III nitride semiconductor electronic device 11 can be provided on the Al _X Ga _1-X N support base. Alternatively, as shown in FIG. 1 (d), the support base 21 includes a group III nitride layer 31a that provides the semiconductor surface 21a and a support 31b made of a different material from Al _X Ga _1-X N. Can be included. The group III nitride layer 31a is mounted on the support 31b. A semiconductor stack 19 for the group III nitride semiconductor electronic device 11 can be provided on the Al _X Ga _1-X N template. The group III nitride layer 31a is made of Al _X Ga _1-X N. As the support 31b, for example, a sapphire substrate, a SiC substrate, a Si substrate, or the like can be used. As a matter of course, a nitride semiconductor substrate such as an AlN substrate or an AlGaN substrate can be used as the support base 21.

If necessary, a buffer layer made of a group III nitride semiconductor can be provided between the support base 21 and the first and second semiconductor layers 13 and 15, and this buffer layer is made of Al _X Ga _1. It preferably consists of _-XN . This buffer layer can be provided in the semiconductor stack 19.

  The channel layer and the barrier layer of the group III nitride semiconductor electronic device 11 include a first semiconductor layer 13 and a second semiconductor layer 15, respectively. The first semiconductor layer 13 forms a heterojunction 27a with the second semiconductor layer 15. A two-dimensional electron gas 29 is generated at the heterojunction 27a. The two-dimensional electron gas 29 is controlled by the electric field from the gate electrode 17. Further, when a voltage is applied to the source electrode 23 and the drain electrode 25, a current flows in the channel from the two-dimensional electron gas 29 in the direction from the drain electrode 25 to the source electrode 23. The source electrode 23 and the drain electrode 25 are electrically connected to the channel layer, and the source electrode 23 and the drain electrode 25 make ohmic contacts J 1 and J 2 with the semiconductor stack 19. The gate electrode 17 forms a Schottky junction JS in the semiconductor stack 19.

  As shown in part (a) of FIG. 1, the gate electrode 17, the source electrode 23, and the drain electrode 25 extend in a predetermined direction (the Y-axis direction of the coordinate system S) on the main surface 19 a of the semiconductor stack 19. The source electrode 23, the gate electrode 17, and the drain electrode 25 are arranged along the main surface 19 a of the semiconductor stack 19 in a direction orthogonal to the predetermined direction (the X-axis direction of the coordinate system S).

  Referring to FIG. 1 (e), an epitaxial substrate EP is shown. The epitaxial substrate EP includes an epitaxial stack 20 and a substrate 22. Epitaxial laminate 20 is provided on main surface 22 a of substrate 22. Epitaxial stack 20 includes a plurality of group III nitride semiconductor layers that can provide substantially the same structure as semiconductor stack 19 including semiconductor layers 13 and 15. The substrate 22 has substantially the same structure and material as the support base 21. In an exemplary embodiment, the epitaxial stack 20 of the epitaxial substrate EP includes a first semiconductor layer 14 for the channel layer (corresponding to the first semiconductor layer 13) and a second semiconductor for the barrier layer. A layer 16 (corresponding to the second semiconductor layer 15) is provided.

In the following two cases, the epitaxial substrate EP for the group III nitride semiconductor electronic device 11 can be provided with a thick semiconductor layer 16 that separates the gate electrode from the current path in the semiconductor stack: first semiconductor layer 14 Has a thickness larger than the critical film thickness defined by the composition of the first group III nitride semiconductor material that contains strain and is unstrained, and the composition of the second group III nitride semiconductor material. Group nitride semiconductor has; first semiconductor layer 14 contains strain and is lattice relaxed with respect to Al _X Ga _1-X N on semiconductor surface 22a.

In a preferred embodiment, the first semiconductor layer 13 is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X) containing strain, and the second semiconductor layer 15 is made of al _Z Ga _1-Z N consists (0 <Z ≦ 1, Z ≦ X). The thickness of the _{Al Z Ga 1-Z} N of the second semiconductor layer 15 can be increased than the critical thickness as defined by the unstrained of _{Al Y Ga 1-Y} N. It can provide a thick _{Al Z Ga 1-Z} N to the second semiconductor layer 15 for the barrier. Aluminum composition of Al _Z Ga _1-Z N is greater than the aluminum mole fraction of _{Al Y Ga 1-Y N,} Al Y Ga 1-Y aluminum composition of N is less than the aluminum composition of _{Al X Ga 1-X} N. In this embodiment, the first semiconductor layer 13 is made of GaN or AlGaN, and the second semiconductor layer 15 is made of AlGaN larger than the aluminum composition of the first semiconductor layer 13. The lattice constant (strained lattice constant) of Al _Y Ga _1-Y N of the first semiconductor layer 13 is the same as that of the underlying Al _X Ga _1-X N and unstrained Al _Y Ga _1- It is between the lattice constant of the _{Y N.} Since the second semiconductor layer 15 is provided on the first semiconductor layer 13 having the intermediate lattice constant, the critical film thickness of the second semiconductor layer 15 is defined based on the intermediate lattice constant. The critical film thickness of Al _Z Ga ₁ -ZN of the second semiconductor layer 15 is larger than the critical film thickness defined by the unstrained lattice constant inherent to Al _Y Ga ₁ -YN.

In practically important embodiments, it is preferred that Al _X Ga _1-X N is AlN. At this time, low dislocation AlN can be used as the support substrate. For example, AlN can have a threading dislocation density of 1 × 10 ⁸ cm ⁻² or less.

The relationship between the lattice constants of the first semiconductor layer 13, the second semiconductor layer 15, and the support base 21 will be described with reference to FIG. 2 (a) and 2 (b), the horizontal axis represents the lattice constant of the a-axis of hexagonal group III nitride changing with an increase in Al composition from GaN to AlN. A vertical axis | shaft shows the Z axis | shaft of the coordinate system shown by the (a) part of FIG. The horizontal axis shows the lattice constant d0 (X) specific to Al _X Ga _1-X N, the lattice constant d0 (Y) specific to Al _Y Ga _1-Y N, and the characteristic specific to Al _Z Ga _1-Z N. The lattice constant d0 (Z) is shown. These inherent lattice constants mean that each material is unstrained. Referring to FIGS. 2A and 2B, a one-dot chain line representing inherent lattice constants d0 (X), d0 (Y), and d0 (Z) is drawn along the vertical axis.

FIG. 2A shows an epitaxial structure ES1 for the group III nitride semiconductor electronic device 11. FIG. In the epitaxial structure ES1, the first semiconductor layer 13 contains strain and is lattice-relaxed on Al _X Ga _1-X N on the semiconductor surface 21a. The second semiconductor layer 15 is provided on the first semiconductor layer 13 in a coherent manner.

Part (b) of FIG. 2 shows an epitaxial structure ESC for a group III nitride semiconductor electronic device different from the group III nitride semiconductor electronic device 11. The epitaxial structure ESC is a third semiconductor layer 33 (associated with the first semiconductor layer 13) for the channel layer and a fourth semiconductor layer 35 (associated with the first semiconductor layer 15) for the barrier layer. Is provided. The third semiconductor layer 33 is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X), and Al _X Ga _1-X N semiconductor surface 21a does not contain distortion. Above, the lattice is completely relaxed. The second semiconductor layer 35 is provided coherently on the _{Al Z Ga 1-Z N (} 0 <Z ≦ 1, Z ≦ X) consists, also the first semiconductor layer 33.

Referring to part (a) of FIG. 2, the lattice constant d (13) of the first semiconductor layer 13 has a value between the inherent lattice constant d0 (Y) and the inherent lattice constant d0 (X). . This indicates that the first semiconductor layer 13 has a so-called intermediate relaxation (or partial relaxation) state in which the lattice matching with Al _X Ga _1-X N is not performed and the lattice is not completely relaxed. (The first semiconductor layer 13 is in a state of being subjected to compressive strain.) The second semiconductor layer 15 is provided coherently on the first semiconductor layer 13 and has a slight amount as indicated by an arrow ST1. It has strain (tensile strain) and has a lattice constant d (15) equal to the lattice constant d (13) of the first semiconductor layer 13.

Referring to FIG. 2B, the semiconductor stack 39 includes a third semiconductor layer 33 and a fourth semiconductor layer 35. The lattice constant d (33) of the third semiconductor layer 33 has a value equal to the inherent lattice constant d0 (Y). This indicates that the third semiconductor layer 33 does not lattice match with Al _X Ga _1-X N and is completely lattice relaxed. The fourth semiconductor layer 35 is provided on the third semiconductor layer 33 coherently, and has a lattice constant d (35) equal to the lattice constant d (33) of the first semiconductor layer 33. The semiconductor layer 35 contains distortion.

The second semiconductor layer 15 contains a small strain as shown by an arrow ST1, while the fourth semiconductor layer 35 contains a large strain as shown by an arrow ST2. Accordingly, although the second semiconductor layer 15 and the fourth semiconductor layer 35 is made of both Al Z _Ga 1-Z _N, due to the difference of the distortion, the critical thickness of the second semiconductor layer 15 is first 4 is larger than the critical film thickness of the semiconductor layer 35.

  The degree of relaxation of the first semiconductor layer 13 shown in part (a) of FIG. 2 is an example, and the electronic device and epitaxial substrate of this embodiment are shown in part (a) of FIG. It is not limited to a specific example.

The semiconductor surface of Al _X Ga _1-X N preferably has a c-plane. At this time, in the first semiconductor layer 13, sliding in the c-plane direction is used to release internal strain. In the case of a c-plane smooth surface, defects based on lattice mismatch do not propagate in the direction of the surface 13 a of the first semiconductor layer 13. Therefore, the heterojunction 27a between the first semiconductor layer 13 and the second semiconductor layer 15 is not directly affected by defects due to the release of internal strain. Further, the heterojunction 27a extends along a plane parallel to the c-plane, and the junction 27b extends along a plane parallel to the c-plane.

In one embodiment, the first semiconductor layer 13 is made of ternary AlGaN, and the second semiconductor layer 15 is made of ternary AlGaN. The ternary AlGaN of the first semiconductor layer 13 forms a junction with Al _X Ga _1-X N of the semiconductor main surface 21a. The group III nitride semiconductor electronic device 11 is provided with an AlGaN / AlGaN heterojunction 27a. A two-dimensional electron gas 29 is formed at the heterojunction 27a. This electron gas is controlled by the electric field from the gate electrode 17 through the second semiconductor layer 15 (AlGaN barrier of this embodiment). This thick AlGaN barrier can provide the group III nitride semiconductor electronic device 11 with a technical contribution that will be described later. The thickness of the AlGaN barrier can be, for example, 20 nm or more, and preferably 30 nm or more. Further, the thickness of the AlGaN barrier can be, for example, 300 nm or less. When the thickness of the AlGaN barrier layer is considerably thick (for example, 40 nm or more), it is preferable to form a recess directly under the electrode in order to reduce the ohmic resistance when forming the ohmic electrode.

In another embodiment, the first semiconductor layer 13 is made of binary GaN, and the second semiconductor layer 15 is made of ternary AlGaN. The binary GaN of the first semiconductor layer 13 forms a junction with Al _X Ga _1-X N of the semiconductor main surface 21a. The group III nitride semiconductor electronic device 11 is provided with an AlGaN / GaN heterojunction 27a. A two-dimensional electron gas is formed at the heterojunction 27a. This electron gas is controlled by the electric field from the gate electrode 17 through the second semiconductor layer 15 (AlGaN barrier of this embodiment). This thick AlGaN barrier can provide the group III nitride semiconductor electronic device 11 with a technical contribution that will be described later. The thickness of the AlGaN barrier can be 20 nm, for example, and is preferably 30 nm or more. Further, the thickness of the AlGaN barrier can be, for example, 300 nm or less. When the thickness of the AlGaN barrier layer is considerably thick (for example, 40 nm or more), it is preferable to form a recess directly under the electrode in order to reduce the ohmic resistance when forming the ohmic electrode.

When the first semiconductor layer 13 is made of Al _Y Ga _1-Y N, the lattice relaxation rate R of the first semiconductor layer 13 is, for example, (d (Al _Y Ga _1-Y N) -d (Al _X Ga _{1- X N))} is defined by _{/ (d0 (Al Y Ga 1} -Y N) -d0 (Al X Ga 1-X N)). The lattice relaxation rate R is preferably greater than zero and 0.9 or less. Further, preferably, the lattice relaxation rate R is larger than zero and 0.8 or less.
_{Here, d0 (Al Y Ga 1-} Y N) represents the lattice constant of the unstrained of _{Al Y Ga 1-Y} N, said _{d0 (Al X Ga 1-X} N) is the unstrained _Al X _{Ga 1-} shows the lattice constants of the _X N, _also, d (Al _{Y Ga 1-Y} N) represents the lattice constant of _Al Y _{Ga 1-Y} N in the III nitride semiconductor electronic device 11, the d (Al _X Ga _1-X N) represents a lattice constant in the group III nitride semiconductor electronic device 11.
According to this embodiment, the thickness of the second semiconductor layer 15 can be made larger than the conventional critical thickness. Further, it is possible to reduce the influence of current collapse or the like by the virtual gate by separating the distance between the epi surface and the two-dimensional electron gas.

When the first semiconductor layer 13 and the second semiconductor layer 15 are made of Al _Y Ga _1-Y N and Al _Z Ga _1-Z N, respectively, the second semiconductor layer 15 and the first semiconductor layer 13 The difference in aluminum composition is preferably 0.17 or more, and the thickness of the second semiconductor layer 15 is preferably larger than 140 nm. The thickness is thicker than the critical thickness of the conventional AlGaN barrier layer _{(Al Z Ga 1-Z N} ), becomes thereby possible to reduce the influence of such current collapse than conventional. In addition, the difference in aluminum composition between the second semiconductor layer 15 and the first semiconductor layer 13 is preferably 0.22 or more, and the thickness of the second semiconductor layer 15 is preferably greater than 92 nm. The thickness is thicker than the critical thickness of the conventional AlGaN barrier layer _{(Al Z Ga 1-Z N} ), becomes thereby possible to reduce the influence of such current collapse than conventional. Furthermore, the difference in aluminum composition between the second semiconductor layer 15 and the first semiconductor layer 13 is preferably 0.37 or more, and the thickness of the second semiconductor layer 15 is preferably greater than 30 nm. The thickness is thicker than the critical thickness of the conventional AlGaN barrier layer _{(Al Z Ga 1-Z N} ), becomes thereby possible to reduce the influence of such current collapse than conventional.

  It will be explained that the critical film thickness of the semiconductor layer for the barrier can be increased by adjusting the lattice relaxation rate of the channel layer. In the experiments of the inventors, for example, the lattice relaxation rate of a channel layer made of GaN or AlGaN is changed. That is, it is grown on the channel layer by creating an intermediate lattice relaxation of 90% or less (for example, 90% relaxation or 80% relaxation) in the channel layer, instead of being completely relaxed (100% relaxation). The critical film thickness of the AlGaN barrier layer can be increased several times.

  Next, an experiment showing that the lattice relaxation rate can be adjusted will be described. In these experiments, the resulting increase in critical film thickness in the AlGaN barrier layer is also described. As far as the inventors know, in AlGaN channel HEMT and GaN channel HEMT, the thickness of the barrier layer depends on its Al composition, but is generally about 15 nm to 30 nm, for example.

(Experiment 1-1)
In an AlGaN / GaN HEMT, an GaN channel layer is relaxed at a lattice relaxation rate of 100%.
A (0001) plane sapphire substrate is prepared. After setting the sapphire substrate in the growth furnace, heat treatment of the sapphire substrate is performed in a hydrogen (H ₂ ) atmosphere at 1100 degrees Celsius. Thereafter, an AlN film having a thickness of 100 nm is grown on the sapphire substrate at a temperature of 1100 degrees Celsius by metal organic vapor phase epitaxy. A 3 μm thick GaN channel film is grown on the AlN film at a temperature of 1050 degrees Celsius. An AlGaN barrier film is grown on the GaN film at a temperature of 1050 degrees Celsius. AlGaN barrier films having Al compositions of 0.17, 0.22, and 0.37 are grown, and the critical film thicknesses of these AlGaN films are examined. When X-ray reciprocal lattice mapping of the GaN channel film is measured, the measurement result shows that the GaN channel film is relaxed at a lattice relaxation rate of 100% with respect to the underlying AlN. From the film formation and measurement results as described above, the relationship between the Al composition of the AlGaN barrier layer and its critical film thickness can be obtained.

(Experiment 1-2)
In an AlGaN / GaN HEMT, an GaN channel layer is relaxed at a lattice relaxation rate of 90%.
A sapphire substrate is prepared as in Experiment 1-1. After setting the sapphire substrate in the growth furnace, heat treatment is performed on the sapphire substrate in a hydrogen (H ₂ ) atmosphere at 1200 degrees Celsius. Thereafter, an AlN film having a thickness of 1000 nm is grown on the sapphire substrate at a temperature of 1200 degrees Celsius by metal organic vapor phase epitaxy. A GaN channel film having a thickness of 0.5 μm is grown on the AlN film at a temperature of 1050 degrees Celsius. An AlGaN barrier film is grown on the GaN film at a temperature of 1050 degrees Celsius. AlGaN barrier films having Al compositions of 0.17, 0.22, and 0.37 are grown, and the critical film thicknesses of these AlGaN films are examined. When the X-ray reciprocal lattice mapping of the GaN channel film is measured, the measurement result shows that the GaN channel film is relaxed at a lattice relaxation rate of 90% with respect to the underlying AlN. From the above film formation and measurement, the relationship between the Al composition of the AlGaN barrier layer and its critical film thickness can be obtained.

(Experiment 2-1)
In an AlGaN / AlGaN (Al composition 0.20) HEMT, an AlGaN channel layer is relaxed at a lattice relaxation rate of 100%.
A sapphire substrate is prepared as in Experiment 1. After setting the sapphire substrate in the growth furnace, heat treatment of the sapphire substrate is performed in a hydrogen (H ₂ ) atmosphere at 1100 degrees Celsius. Thereafter, an AlN film having a thickness of 100 nm is grown on the sapphire substrate at a temperature of 1100 degrees Celsius by metal organic vapor phase epitaxy. An AlGaN channel film (Al composition = 0.20) having a thickness of 3 μm is grown on the AlN film at a temperature of 1050 degrees Celsius. An AlGaN barrier film is grown on the AlGaN film at a temperature of 1050 degrees Celsius. An AlGaN barrier film having an Al composition of 0.37, 0.42, and 0.57 is grown, and the AlGaN film of the heterojunction in which the composition difference between the channel layer and the barrier layer is 0.17, 0.22, and 0.37. Examine the critical film thickness. When the X-ray reciprocal lattice mapping of the AlGaN channel film is measured, the measurement result shows that the AlGaN channel film is relaxed at a lattice relaxation rate of 100% with respect to the underlying AlN. From the above film formation and measurement, the relationship between the Al composition of the AlGaN barrier layer and its critical film thickness can be obtained.

(Experiment 2-2)
In an AlGaN / AlGaN (Al composition 0.20) HEMT, an AlGaN channel layer is relaxed at a lattice relaxation rate of 90%.
A sapphire substrate is prepared as in Experiment 1-1. After setting the sapphire substrate in the growth furnace, heat treatment is performed on the sapphire substrate in a hydrogen (H ₂ ) atmosphere at 1200 degrees Celsius. Thereafter, an AlN film having a thickness of 1000 nm is grown on the sapphire substrate at a temperature of 1200 degrees Celsius by metal organic vapor phase epitaxy. An AlGaN channel film (Al composition = 0.20) having a thickness of 1 μm is grown on the AlN film at a temperature of 1050 degrees Celsius. An AlGaN barrier film is grown on the AlGaN film at a temperature of 1050 degrees Celsius. An AlGaN barrier film having an Al composition of 0.37, 0.42, and 0.57 is grown, and the AlGaN film of the heterojunction in which the composition difference between the channel layer and the barrier layer is 0.17, 0.22, and 0.37. Examine the critical film thickness. When the X-ray reciprocal lattice mapping of the AlGaN channel film is measured, the measurement result shows that the AlGaN channel film is relaxed at a lattice relaxation rate of 90% with respect to the underlying AlN. From the above film formation and measurement, the relationship between the Al composition of the AlGaN barrier layer and its critical film thickness can be obtained.

(Experiment 2-3)
In an AlGaN / AlGaN (Al composition 0.20) HEMT, an AlGaN channel layer is relaxed at a lattice relaxation rate of 80%.
A sapphire substrate is prepared as in Experiment 1-1. After setting the sapphire substrate in the growth furnace, heat treatment is performed on the sapphire substrate in a hydrogen (H ₂ ) atmosphere at 1250 degrees Celsius. Thereafter, an AlN film having a thickness of 1500 nm is grown on the sapphire substrate at a temperature of 1250 degrees Celsius by metal organic vapor phase epitaxy. An AlGaN channel film (Al composition = 0.20) having a thickness of 0.5 μm is grown on the AlN film at a temperature of 1050 degrees Celsius. An AlGaN barrier film is grown on the AlGaN film at a temperature of 1050 degrees Celsius. An AlGaN barrier film having an Al composition of 0.37, 0.42, and 0.57 is grown, and the AlGaN film of the heterojunction in which the composition difference between the channel layer and the barrier layer is 0.17, 0.22, and 0.37. Examine the critical film thickness. When the X-ray reciprocal lattice mapping of the AlGaN channel film is measured, the measurement result shows that the AlGaN channel film is relaxed at a lattice relaxation rate of 80% with respect to the underlying AlN. From the above film formation and measurement, the relationship between the Al composition of the AlGaN barrier layer and its critical film thickness can be obtained.
Since the crystallinity of AlN is better as the growth temperature of AlN is higher and the thickness of AlN is thicker, the relaxation of the channel layer on AlN is more difficult to relax as the crystallinity is better. It can be seen that there is a tendency (less than 100% relaxation). For example, the crystallinity of AlN was about 1500 arcsec in Example 2-1, about 800 arcsec in Example 2-2, and about 600 arcsec in Example 2-2.

(Experiment 3-1)
An epitaxial substrate in which an AlGaN channel layer is relaxed at a lattice relaxation rate of 100% in an AlGaN / AlGaN (Al composition 0.50) HEMT.
A sapphire substrate is prepared as in Experiment 1-1. After setting the sapphire substrate in the growth furnace, heat treatment of the sapphire substrate is performed in a hydrogen (H ₂ ) atmosphere at 1100 degrees Celsius. Thereafter, an AlN film having a thickness of 100 nm is grown on the sapphire substrate at a temperature of 1100 degrees Celsius by metal organic vapor phase epitaxy. An AlGaN channel film (Al composition = 0.50) having a thickness of 3 μm is grown on the AlN film at a temperature of 1100 degrees Celsius. An AlGaN barrier film is grown on the AlGaN film at a temperature of 1100 degrees Celsius. An AlGaN barrier film having an Al composition of 0.67, 0.72, and 0.87 is grown, and the AlGaN film in the heterojunction in which the composition difference between the channel layer and the barrier layer is 0.17, 0.22, and 0.37. Examine the critical film thickness. When the X-ray reciprocal lattice mapping of the AlGaN channel film is measured, the measurement result shows that the AlGaN channel film is relaxed at a lattice relaxation rate of 100% with respect to the underlying AlN. From the above film formation and measurement, the relationship between the Al composition of the AlGaN barrier layer and its critical film thickness can be obtained.

(Experiment 3-2)
An epitaxial substrate in which an AlGaN channel layer is relaxed at a lattice relaxation rate of 90% in an AlGaN / AlGaN (Al composition 0.50) HEMT.
A sapphire substrate is prepared as in Experiment 1-1. After setting the sapphire substrate in the growth furnace, heat treatment is performed on the sapphire substrate in a hydrogen (H ₂ ) atmosphere at 1200 degrees Celsius. Thereafter, an AlN film having a thickness of 1000 nm is grown on the sapphire substrate at a temperature of 1200 degrees Celsius by metal organic vapor phase epitaxy. An AlGaN channel film (Al composition = 0.50) having a thickness of 2 μm is grown on the AlN film at a temperature of 1100 degrees Celsius. An AlGaN barrier film is grown on the AlGaN film at a temperature of 1100 degrees Celsius. An AlGaN barrier film having an Al composition of 0.67, 0.72, and 0.87 is grown, and the AlGaN film in the heterojunction in which the composition difference between the channel layer and the barrier layer is 0.17, 0.22, and 0.37. Examine the critical film thickness. When the X-ray reciprocal lattice mapping of the AlGaN channel film is measured, the measurement result shows that the AlGaN channel film is relaxed at a lattice relaxation rate of 90% with respect to the underlying AlN. From the above film formation and measurement, the relationship between the Al composition of the AlGaN barrier layer and its critical film thickness can be obtained.

(Experiment 3-3)
In an AlGaN / AlGaN (Al composition 0.50) HEMT, an AlGaN channel layer is relaxed at a lattice relaxation rate of 80%.
A sapphire substrate is prepared as in Experiment 1-1. After setting the sapphire substrate in the growth furnace, heat treatment is performed on the sapphire substrate in a hydrogen (H ₂ ) atmosphere at 1250 degrees Celsius. Thereafter, an AlN film having a thickness of 1500 nm is grown on the sapphire substrate at a temperature of 1200 degrees Celsius by metal organic vapor phase epitaxy. An AlGaN channel film (Al composition = 0.50) having a thickness of 1 μm is grown on the AlN film at a temperature of 1100 degrees Celsius. An AlGaN barrier film is grown on the AlGaN film at a temperature of 1100 degrees Celsius. An AlGaN barrier film having an Al composition of 0.67, 0.72, and 0.87 is grown, and the AlGaN film in the heterojunction in which the composition difference between the channel layer and the barrier layer is 0.17, 0.22, and 0.37. Examine the critical film thickness. When the X-ray reciprocal lattice mapping of the AlGaN channel film is measured, the measurement result shows that the AlGaN channel film is relaxed at a lattice relaxation rate of 80% with respect to the underlying AlN. From the above film formation and measurement, the relationship between the Al composition of the AlGaN barrier layer and its critical film thickness can be obtained.

  These experiments and their results are exemplary, and together with the results of the experiments not shown here, the lattice relaxation rate of the channel layer is the channel layer AlGaN film thickness, such as the channel layer GaN film thickness and growth temperature, It can be controlled not only by composition and growth temperature, but also by the growth temperature and film thickness of the underlying AlN. In the above experiment, although an AlN template was used, an experiment using a bulk AlN substrate is an AlGaN epitaxial layer (almost the same as the result in an epitaxial substrate in which an AlN film having a thickness of 1.0 μm is stacked on a sapphire substrate ( An AlGaN layer having a lattice relaxation rate of 80% is obtained. In the experimental example, a sapphire substrate is used, but the same result is obtained even when a different substrate such as a SiC substrate or a Si substrate is used.

According to the experiments by the inventors, the following matters are indicated when the lattice relaxation uses an AlN layer as the base semiconductor layer and AlGaN as the channel layer in the relationship between the base semiconductor layer and the channel semiconductor layer.
(1) The larger the difference in Al composition between the underlying semiconductor layer and the channel semiconductor layer, the greater the relaxation.
(2) The thicker the channel layer, the easier it is to relax.
(3) The thinner the underlying semiconductor layer, the thinner the channel layer grown thereon.
(4) When the crystal quality of the underlying semiconductor layer is not good, the channel layer grown thereon is relaxed with a thin film thickness. A channel layer grown on a high-quality underlying semiconductor layer is likely to obtain a lattice relaxation with an incomplete value of less than 100%.
The AlN layer having a sufficient thickness is almost completely relaxed with respect to the sapphire substrate serving as the base. Also, it can be considered that the AlN substrate is almost completely relaxed in that it has a lattice constant inherent to AlN.

  FIG. 3 shows an example of a reciprocal lattice mapping image of the epitaxial substrate created in the experiment. When AlGaN is deposited on AlN so that it is completely coherent (in this case, the a-axis lattice constant of AlGaN is the same as the a-axis lattice constant of AlN), it is grown. The peak of the AlGaN signal is on a broken line drawn parallel to the vertical axis.

  When the AlGaN layer over AlN grows completely relaxed (that is, the channel layer has the same value as the a-axis lattice constant of unstrained AlGaN), the signal peak of the grown AlGaN is vertical. It lies on a solid line drawn with an inclination to the axis. When the peak of the grown AlGaN signal is located between the solid and dashed lines, intermediate relaxed AlGaN is obtained. A lattice relaxation rate of zero indicates that AlGaN is grown coherently with respect to the underlying layer. When the lattice relaxation rate is 100% (or 1), it is completely relaxed, indicating that there is no distortion due to the difference in lattice constant. The intermediate lattice relaxation rate is expressed as a percentage using the ratio of the lattice constant of the a axis when completely relaxed to the lattice constant of the a axis when completely coherent. Note that AlGaN shown in FIG. 3 corresponds to approximately 80% relaxation.

  FIG. 4 shows a list of the results of the above experiments. FIG. 5 is a drawing showing the relationship between the difference in Al composition between the channel layer and the barrier layer and the critical film thickness of the barrier layer. As the result of FIG. 4 shows, a barrier layer (for example, an AlGaN layer) grown on the channel layer by using a lattice layer having a lattice relaxation rate equal to or less than 90% instead of the usual 100%. The critical film thickness can be increased. Further, by using a channel layer having a lattice relaxation rate equal to or less than 80%, the critical film thickness of a barrier layer (for example, an AlGaN layer) grown on the channel layer can be further increased.

The reason for this will be explained. When comparing an AlGaN channel layer A having an Al composition of 0.2 and a lattice relaxation of 80% with an AlGaN channel layer B having an Al composition of 0.2 and a lattice relaxation of 100%, the lattice constant of the AlGaN channel layer A is that of the AlGaN channel layer B. It is closer to the lattice constant of unstrained AlN than the lattice constant. The strained lattice constant of the AlGaN channel layer A is smaller than the unstrained lattice constant of the AlGaN channel layer B. According to the inventors' estimation, the strained lattice constant of the AlGaN channel layer A is equal to the lattice constant of AlGaN having an Al composition of 0.36 and a lattice relaxation rate of 100%. Therefore, when an AlGaN barrier layer having an Al composition of 0.57 is coherently grown on the AlGaN channel layer A, the Al composition difference of these AlGaN layers is 0.37, but the lattice constant difference of these AlGaN layers is It is substantially 0.21. Therefore, even when a thick barrier layer is grown, lattice relaxation and generation of cracks / defects are unlikely to occur, so that the critical film thickness increases.
In addition, since the AlGaN channel layer having a low aluminum composition, such as the Al composition 0.20, can reduce the influence of alloy scattering compared to the AlGaN channel layer having an Al composition of 0.37, the mobility of electrons in the channel layer can be increased. In addition, the epitaxial growth is also easier as compared with the deposition of AlGaN having a higher Al composition.

As shown in FIG. 4, when the channel layer and the barrier layer are made of Al _Y Ga _1-Y N and Al _Z Ga _1-Z N, respectively, the difference in aluminum composition between the channel layer and the barrier layer is 0. When it is 17 or more, the thickness of the Al _Z Ga _1-Z N of the barrier layer can be larger than 140 nm. When the difference in aluminum composition between the channel layer and the barrier layer is 0.22 or more, the thickness of the barrier layer can be greater than 92 nm. When the difference in aluminum composition between the channel layer and the barrier layer is 0.37 or more, the thickness of the barrier layer can be made larger than 30 nm.

The technical contribution that the critical thickness of the barrier layer can be made larger than the original value will be described. FIG. 6 is a drawing showing a main process flow 100 in the method of manufacturing a group III nitride semiconductor electronic device according to the present embodiment. A high electron mobility transistor, which is an example of a group III nitride semiconductor electronic device, is manufactured according to the process flow 100 as follows. In step S101, a substrate is prepared. This substrate includes, for example, a sapphire substrate and an AlN template produced on the sapphire substrate. Alternatively, a nitride substrate such as an AlN substrate or an AlGaN substrate may be used. In step S102, a channel layer and a barrier layer are grown on this substrate to produce an epitaxial substrate for the HEMT structure. Here, in step S103, a channel surface layer made of a group III nitride semiconductor material different from Al _X Ga _1-X N is formed on a semiconductor surface made of Al _X Ga _1-X N (0 <X ≦ 1). A first semiconductor layer is grown. Next, in step S104, a second semiconductor layer for the barrier layer is grown on the first semiconductor layer. The first semiconductor layer for the channel layer contains strain, and the thickness of the second semiconductor layer is greater than the critical thickness defined by the composition of the unstrained first group III nitride semiconductor material. As an example, this epitaxial substrate includes an AlGaN / AlGaN-based HEMT structure including, for example, an AlGaN channel layer having an Al composition of 0.2 and a lattice relaxation of 80% and an AlGaN barrier layer having an Al composition of 0.57. In these HEMT structures, the thickness of the AlGaN barrier layer is 15 nm, 30 nm, 60 nm and 120 nm. In any HEMT structure, the compositional difference between the barrier layer and the channel layer is 0.37.

  In step S105, an electrode is formed on the epitaxial substrate to produce a HEMT device. Specifically, in step S106, after the channel layer is grown, a gate electrode (for example, Ni / Au) is formed. In step S107, source / drain electrodes (for example, Zr / Al electrodes) are formed on the epitaxial substrate. If necessary, an element isolation region can be formed on the epitaxial substrate, and the transistor on the epitaxial substrate has a mesa structure for element isolation, and this mesa structure is etched using an inductively coupled plasma method. It is processed by. When the source / drain electrode is manufactured, a recess is formed on the surface of the epitaxial substrate, and a part or all of the barrier layer is removed in the depth direction in the area where the source / drain electrode is manufactured, so that an ohmic contact can be easily obtained. I am doing so. The HEMT device has a gate length of 1 μm, a gate-drain distance of 5 μm, and a source-drain distance of 1 μm.

The current collapse of these HEMT devices is evaluated. As the evaluation method, the following procedure is used: (1) First, the maximum drain current (Id-1) is measured at the gate voltage at +1 volt; Apply a voltage of -200 volts. After 1 millisecond from the start of this voltage application, the maximum drain current (Id-2) is measured at the gate voltage at +1 volt; the drain current ratio (Id-1) / (Id-2) is determined. The closer the drain current ratio is to 1, the greater the influence of current collapse.
Barrier layer thickness, current ratio (Id-1) / (Id-2).
15 nm, 0.13.
30 nm, 0.43.
60 nm, 0.68.
120 nm, 0.81.
Thus, using a thick barrier layer is effective in suppressing current collapse.
As a possible reason for this, the influence of the surface of the epitaxial AlGaN barrier layer (for example, the influence of a virtual gate, etc.) can be obtained by providing thick AlGaN to the barrier layer, thereby increasing the main surface of the AlGaN barrier layer. It is thought that the influence of carrier traps on the epi surface could be reduced because the distance to the dimensional electron gas was increased.

Similarly, a gate recess is formed in the HEMT structure, and a gate field plate is formed. The current collapse suppression effect and dielectric strength of this HEMT device are measured. The measurement results are shown below.
Barrier layer thickness, dielectric strength, current ratio (Id-1) / (Id-2).
15 nm, 820 V, 0.13.
30 nm, 1120 V, 0.43.
60 nm, 1420 V, 0.68.
120 nm, 1620 V, 0.81.
These measurements show that when a gate field plate is fabricated, it is effective not only for current collapse but also for improving the breakdown voltage. As described above, in addition to the above two technical contributions, various effects can be obtained by growing a thick barrier layer. Note that these effects can provide an electronic device with a thicker barrier layer by using a distorted channel layer.

  The present invention is not limited to the specific configuration disclosed in the present embodiment.

  As described above, according to the present embodiment, there is provided a group III nitride semiconductor electronic device capable of increasing the thickness of the semiconductor layer separating the gate electrode from the current path in the semiconductor stack. In addition, according to the present embodiment, an epitaxial substrate for a group III nitride semiconductor electronic device is provided. Furthermore, according to the present embodiment, a method for producing a group III nitride semiconductor electronic device is provided.

DESCRIPTION OF SYMBOLS 11 ... III nitride semiconductor electronic device, 13 ... 1st semiconductor layer, 14 ... 1st semiconductor layer, 15 ... 2nd semiconductor layer, 16 ... 2nd semiconductor layer, 17 ... Gate electrode, 19 ... Semiconductor Laminated, 20 ... epitaxial laminated body, 21a ... semiconductor surface, 21 ... supporting base, 22 ... substrate, 22 ... semiconductor laminated, 22a ... semiconductor surface, 27a ... heterojunction, 23 ... source electrode, 25 ... drain electrode, 29 ... two Dimensional electron gas, 31a ... group III nitride layer, 31b ... support, J1, J2 ... ohmic contact, JS ... Schottky junction, EP ... epitaxial substrate.

Claims (25)

A group III nitride semiconductor electronic device comprising:
A _first semiconductor layer provided on a semiconductor surface made of Al _X Ga _1-X N (0 <X ≦ 1) and made of a first group III nitride semiconductor material;
A second semiconductor layer comprising a second group III nitride semiconductor material having a bandgap greater than that of the first group III nitride semiconductor material;
A gate electrode provided on the second semiconductor layer;
With
The second semiconductor layer is provided on the first semiconductor layer;
The first group III nitride semiconductor material is different from the Al _X Ga _1-X N,
The first semiconductor layer contains strain and is lattice-relaxed on Al _X Ga _1-X N on the semiconductor surface ,
The thickness of the second semiconductor layer is larger than the critical film thickness defined by the composition of the unstrained first group III nitride semiconductor material and the composition of the second group III nitride semiconductor material. Nitride semiconductor electronic devices. The first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X),
Said second semiconductor layer comprises _{Al Z Ga 1-Z N (} 0 <Z ≦ 1, Z ≦ X),
The aluminum composition of the Al _Z Ga _1-Z N is larger than the aluminum composition of the Al _Y Ga _1-Y N,
The group III nitride semiconductor electronic device according to claim 1, wherein an aluminum composition of the Al _Y Ga _1-Y N is smaller than an aluminum composition of the Al _X Ga _1-X N. The channel layer of the group III nitride semiconductor electronic device includes the first semiconductor layer;
The barrier layer of the group III nitride semiconductor electronic device includes the second semiconductor layer,
The first semiconductor layer is made of ternary AlGaN,
The second semiconductor layer is made of ternary AlGaN;
3. The group III nitride semiconductor electronic device according to claim 1 , wherein AlGaN of the first semiconductor layer forms a junction with Al _X Ga _1-X N of the semiconductor surface . The channel layer of the group III nitride semiconductor electronic device includes the first semiconductor layer;
The barrier layer of the group III nitride semiconductor electronic device includes the second semiconductor layer,
The first semiconductor layer is made of binary GaN;
The second semiconductor layer is made of ternary AlGaN;
3. The group III nitride semiconductor electronic device according to claim 1 , wherein GaN of the first semiconductor layer forms a junction with Al _X Ga _1-X N on the semiconductor surface . The first semiconductor layer forms a heterojunction with the second semiconductor layer;
5. The group III nitride semiconductor electronic device according to claim 1 , wherein the second semiconductor layer is provided coherently on the first semiconductor layer. 6. The first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X),
The first semiconductor layer has a lattice relaxation rate R;
The lattice relaxation rate R _{(d (Al Y Ga 1-} Y N) -d (Al X Ga 1-X N)) / (d0 (Al Y Ga 1-Y N) -d0 (Al X Ga 1-X N)), where d0 (Al _Y Ga _1-Y N) represents the lattice constant of unstrained Al _Y Ga _1-Y N, and d 0 (Al _X Ga _1-X N) is The lattice constant of unstrained Al _X Ga _1-X N is shown, and the d (Al _Y Ga _1-Y N) is the lattice constant of Al _Y Ga _1-Y N in the group III nitride semiconductor electronic device. , D (Al _X Ga _1-X N) represents the lattice constant of Al _X Ga _1-X N in the group III nitride semiconductor electronic device,
The group III nitride semiconductor electronic device according to any one of claims 1 to 5 , wherein the lattice relaxation rate R is greater than zero and equal to or less than 0.9. The first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X),
The first semiconductor layer has a lattice relaxation rate R;
The lattice relaxation rate R _{(d (Al Y Ga 1-} Y N) -d (Al X Ga 1-X N)) / (d0 (Al Y Ga 1-Y N) -d0 (Al X Ga 1-X N)), where d0 (Al _Y Ga _1-Y N) represents the lattice constant of unstrained Al _Y Ga _1-Y N, and d 0 (Al _X Ga _1-X N) is The lattice constant of unstrained Al _X Ga _1-X N is shown, and the d (Al _Y Ga _1-Y N) is the lattice constant of Al _Y Ga _1-Y N in the group III nitride semiconductor electronic device. , D (Al _X Ga _1-X N) represents the lattice constant of Al _X Ga _1-X N in the group III nitride semiconductor electronic device,
The group III nitride semiconductor electronic device according to any one of claims 1 to 6 , wherein the lattice relaxation rate R is greater than zero and equal to or less than 0.8. A support base on which the first and second semiconductor layers are mounted;
The support substrate has the semiconductor surface;
The group III nitride semiconductor electronic device according to any one of claims 1 to 7 , wherein the support base is made of a substrate made of the Al _X Ga _1-X N. A support base on which the first and second semiconductor layers are mounted;
The support base includes a group III nitride layer that provides the semiconductor surface, and a support made of a material different from the Al _X Ga _1-X N,
The group III nitride semiconductor electronic device according to any one of claims 1 to 7 , wherein the group III nitride layer is mounted on the support. The group III nitride semiconductor electronic device according to claim 1 , wherein the Al _X Ga _1-X N is AlN. The group III nitride semiconductor electronic device according to claim 1 , wherein the semiconductor surface of the Al _X Ga _1-X N has a c-plane. The first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X),
Said second semiconductor layer comprises _{Al Z Ga 1-Z N (} 0 <Z ≦ 1, Z ≦ X),
A difference in aluminum composition between the second semiconductor layer and the first semiconductor layer is 0.17 or more;
The thickness of the second semiconductor layer is rather larger than 140 nm, is 300nm or less, III nitride semiconductor electronic device according to any one of claims 1 to 11. The first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X),
Said second semiconductor layer comprises _{Al Z Ga 1-Z N (} 0 <Z ≦ 1, Z ≦ X),
A difference in aluminum composition between the second semiconductor layer and the first semiconductor layer is 0.22 or more;
The thickness of the second semiconductor layer is rather larger than 92 nm, is 300nm or less, III nitride semiconductor electronic device according to any one of claims 1 to 11. The first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X),
Said second semiconductor layer comprises _{Al Z Ga 1-Z N (} 0 <Z ≦ 1, Z ≦ X),
A difference in aluminum composition between the second semiconductor layer and the first semiconductor layer is 0.37 or more;
The thickness of the second semiconductor layer is rather larger than 30 nm, is 300nm or less, III nitride semiconductor electronic device according to any one of claims 1 to 11. An epitaxial substrate for a group III nitride semiconductor electronic device comprising:
A substrate having a semiconductor surface made of Al _X Ga _1-X N (0 <X ≦ 1);
A first semiconductor layer provided on the semiconductor surface, made of a first group III nitride semiconductor material, for a channel layer;
A second semiconductor layer provided on the first semiconductor layer for the barrier layer;
With
The second semiconductor layer is made of a second group III nitride semiconductor material having a band gap larger than that of the first group III nitride semiconductor material;
The first group III nitride semiconductor material is different from the Al _X Ga _1-X N,
The first semiconductor layer contains strain and is lattice-relaxed on Al _X Ga _1-X N on the semiconductor surface ,
The thickness of the second semiconductor layer is larger than the critical film thickness defined by the composition of the unstrained first group III nitride semiconductor material and the composition of the second group III nitride semiconductor material. . The epitaxial substrate according to claim 15, wherein the substrate is made of the Al _X Ga _1-X N. The substrate includes a group III nitride layer that provides the semiconductor surface, and a support made of a material different from the Al _X Ga _1-X N,
The epitaxial substrate according to claim 15, wherein the group III nitride layer is mounted on the support. The epitaxial substrate according to claim 15 , wherein the Al _X Ga _1-X N is AlN. The first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X),
The first semiconductor layer has a lattice relaxation rate R;
The lattice relaxation rate R _{(d (Al Y Ga 1-} Y N) -d (Al X Ga 1-X N)) / (d0 (Al Y Ga 1-Y N) -d0 (Al X Ga 1-X N)),
The epitaxial substrate according to any one of claims 15 to 18, wherein the lattice relaxation rate R is greater than zero and equal to or less than 0.9. The first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X),
The first semiconductor layer has a lattice relaxation rate R;
The lattice relaxation rate R _{(d (Al Y Ga 1-} Y N) -d (Al X Ga 1-X N)) / (d0 (Al Y Ga 1-Y N) -d0 (Al X Ga 1-X N)),
The epitaxial substrate according to any one of claims 15 to 19 , wherein the lattice relaxation rate R is greater than zero and equal to or less than 0.8. The first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X),
Said second semiconductor layer comprises _{Al Z Ga 1-Z N (} 0 <Z ≦ 1, Z ≦ X),
A difference in aluminum composition between the second semiconductor layer and the first semiconductor layer is 0.17 or more;
The thickness of the second semiconductor layer is rather larger than 140 nm, is 300nm or less, an epitaxial substrate according to any one of claims 15 to claim 20. The first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X),
Said second semiconductor layer comprises _{Al Z Ga 1-Z N (} 0 <Z ≦ 1, Z ≦ X),
A difference in aluminum composition between the second semiconductor layer and the first semiconductor layer is 0.22 or more;
The thickness of the second semiconductor layer is rather larger than 92 nm, is 300nm or less, an epitaxial substrate according to any one of claims 15 to claim 20. The first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X),
Said second semiconductor layer comprises _{Al Z Ga 1-Z N (} 0 <Z ≦ 1, Z ≦ X),
A difference in aluminum composition between the second semiconductor layer and the first semiconductor layer is 0.37 or more;
The thickness of the second semiconductor layer is rather larger than 30 nm, is 300nm or less, an epitaxial substrate according to any one of claims 15 to claim 20. A method of fabricating a group III nitride semiconductor electronic device comprising:
Growing a first semiconductor layer made of a first group III nitride semiconductor material on a semiconductor surface made of Al _X Ga _1-X N (0 <X ≦ 1);
Growing a second semiconductor layer on the first semiconductor layer;
Forming a gate electrode after growing the second semiconductor layer;
With
The first group III nitride semiconductor material is different from the Al _X Ga _1-X N,
The second semiconductor layer is made of a second group III nitride semiconductor material having a band gap larger than that of the first group III nitride semiconductor material;
The first semiconductor layer contains strain and is lattice-relaxed on Al _X Ga _1-X N on the semiconductor surface , and the thickness of the second semiconductor layer is the unstrained first A method for producing a group III nitride semiconductor electronic device having a thickness larger than the critical film thickness defined by the composition of the group III nitride semiconductor material. The first semiconductor layer is made of Al _Y Ga _1-Y N (0 ≦ Y <1, Y <Z, Y <X),
Said second semiconductor layer comprises _{Al Z Ga 1-Z N (} 0 <Z ≦ 1, Z ≦ X),
The aluminum composition of the Al _Z Ga _1-Z N is larger than the aluminum composition of the Al _Y Ga _1-Y N,
The _{Al Y Ga 1-Y} aluminum composition of N is aluminum composition smaller than the _{Al X Ga 1-X} N, a method of fabricating a group III nitride semiconductor electronic device according to claim 24.