JP4984425B2 - Field effect transistor and epitaxial substrate - Google Patents

Description

  The present invention relates to a field effect transistor and an epitaxial substrate.

Non-Patent Document 1 describes a field effect transistor having a heterostructure. This field effect transistor has an AlGaN / GaN / AlN structure, and includes an AlN layer, an undoped GaN layer, and an AlGaN layer sequentially provided on the Al surface of the AlN substrate. The gate electrode forms a Schottky junction with the AlGaN layer. In this field effect transistor, an undoped GaN layer is located between the AlN layer and the AlGaN layer, and the band gap of the substrate material is larger than the band gap of AlGaN.
Applied PhysicsLetters, 82 (2003) pp.1299-1301

  According to the inventor's knowledge, in the field effect transistor described in Non-Patent Document 1, a two-dimensional electron gas is generated at the AlGaN / GaN interface. Furthermore, two-dimensional hole gas is generated at the AlN / GaN interface. In this field effect transistor, not only a two-dimensional electron gas but also a two-dimensional hole gas contributes to electrical conduction. Since this two-dimensional hole gas is less likely to be controlled by the gate electrode provided on the AlGaN layer than the two-dimensional electron gas, transistor characteristics are deteriorated.

  The present invention provides a field effect transistor having a structure capable of avoiding electrical conduction of a two-dimensional hole gas and comprising a nitride material having a Wruzite structure, and an epitaxial substrate for the field effect transistor. Objective.

According to one aspect of the present invention, a field effect transistor includes: (a) an Al _X Ga _1-X N supporting base (0 <X ≦ 1) having a Wruzite structure; and (b) the Al _X Ga _1-X N supporting. a _{Al X Ga 1-X} N epitaxial layer provided on the N surface of the substrate, (c) said _{Al X Ga 1-X} N _Al provided on the epitaxial layer Y _{Ga 1-Y} N epitaxial layer (0 ≦ Y <1, Y <X), (d) a gate electrode forming a Schottky junction with the Al _Y Ga _1- YN epitaxial layer, and (e) provided on the Al _Y Ga _1-YN epitaxial layer. A source electrode; and (f) a drain electrode provided on the Al _Y Ga _1-Y N epitaxial layer.

This field effect transistor includes a heterojunction of an Al _X Ga _1-X N epitaxial layer and an Al _Y Ga _1-Y N epitaxial layer provided on the N surface of the Al _X Ga _1-X N support base. Therefore, the two-dimensional electron gas at the interface of the heterojunction contributes to the conduction of the transistor without forming a two-dimensional hole gas in the field effect transistor.

In the field effect transistor according to the present invention, the Al _X Ga _1-X N epitaxial layer preferably has a thickness of 50 nm or more. If the thickness of the Al _X Ga _1-X N epitaxial layer is 50 nm or more, Al _X Ga _1-X N with good crystal quality can be formed.

In the field effect transistor of one aspect of the present invention, the thickness of the Al _Y Ga _1-Y N epitaxial layer is preferably 1 nm or more and 100 nm or less. In this field effect transistor, since the thickness of the Al _Y Ga _1-Y N epitaxial layer is 1 nm or more, a two-dimensional electron gas having a sufficient density is accumulated. Moreover, if the thickness of the Al _Y Ga _1-Y N epitaxial layer is 100 nm or less, it is possible to form Al _Y Ga _1-Y N having good crystal quality on the Al _X Ga _1-X N layer.

According to another aspect of the present invention, a field effect transistor includes: (a) an AlN support base having a Wruzite structure; (b) an AlN epitaxial layer provided on the N surface of the AlN support base; An Al _Y Ga _1-Y N epitaxial layer (0 <Y <1) provided on the AlN epitaxial layer, (d) an electrode forming a Schottky junction with the Al _Y Ga _1-Y N epitaxial layer, and (e) A source electrode provided on the Al _Y Ga _1-Y N epitaxial layer; and (f) a drain electrode provided on the Al _Y Ga _1-Y N epitaxial layer.

Since this field effect transistor includes a heterojunction of an AlN epitaxial layer and an Al _Y Ga ₁ -YN epitaxial layer provided on the N surface of the AlN support base, two-dimensional hole gas is formed in the field effect transistor. Instead, the two-dimensional electron gas at the interface of the heterojunction contributes to the conduction of the transistor.

  In the field effect transistor according to another aspect of the present invention, the thickness of the AlN epitaxial layer is preferably 50 nm or more. According to this field effect transistor, if the thickness of the AlN epitaxial layer is 50 nm or more, it is possible to form AlN with good crystal quality.

According to another aspect of the present invention, in the field effect transistor, the Al _Y Ga _1-Y N epitaxial layer preferably has a thickness of 1 nm or more and 100 nm or less. In this field effect transistor, since the thickness of the Al _Y Ga _1-Y N epitaxial layer is 1 nm or more, a two-dimensional electron gas having a sufficient density is accumulated. Moreover, if the thickness of the Al _Y Ga _1-Y N epitaxial layer is 100 nm or less, AlGaN with good crystal quality can be formed on the AlN layer.

  According to another aspect of the present invention, a field effect transistor includes: (a) an AlN support base having a Wruzite structure; (b) an AlN epitaxial layer provided on the N surface of the AlN support base; A GaN epitaxial layer provided on the AlN epitaxial layer; (d) a gate electrode forming a Schottky junction with the GaN epitaxial layer; (e) a source electrode provided on the AlN epitaxial layer; and (f) the AlN. And a drain electrode provided on the epitaxial layer.

  Since the heterojunction of the AlN epitaxial layer and the GaN epitaxial layer provided on the N surface of the AlN support base is included, two-dimensional hole gas is not formed in the field effect transistor, and the interface between the heterojunction two layers is formed. The dimensional electron gas contributes to the conduction of the transistor.

  In the field effect transistor according to another aspect of the present invention, the thickness of the AlN epitaxial layer is preferably 50 nm or more. According to this field effect transistor, if the thickness of the AlN epitaxial layer is 50 nm or more, it is possible to form AlN with good crystal quality.

  In the field effect transistor according to another aspect of the present invention, the thickness of the GaN epitaxial layer is preferably 1 nm or more and 100 nm or less. According to this field effect transistor, since the thickness of the GaN epitaxial layer is 1 nm or more, a two-dimensional electron gas having a sufficient density is accumulated. Moreover, if the thickness of the GaN epitaxial layer is 100 nm or less, GaN with good crystal quality can be formed on the AlN layer.

  In the field effect transistor according to some aspects of the present invention, the source electrode material preferably includes at least one of Ti, Al, Au, Pt, Pd, and Mo, and the drain electrode material is , Ti, Al, Au, Pt, Pd, and Mo are preferably included. According to the field effect transistor, a suitable source electrode and drain electrode are provided.

  In the field effect transistor according to some aspects of the present invention, the material of the gate electrode preferably includes at least one of Ni, Au, Pt, and Pd. According to the field effect transistor, a Schottky junction suitable for the gate electrode is provided.

According to still another aspect of the present invention, an epitaxial substrate includes: (a) an Al _X Ga _1-X N substrate (0 <X ≦ 1) having a Wruzite structure; and (b) the Al _X Ga _1-X N a _{Al X Ga 1-X} N epitaxial film provided on the N surface of the substrate, (c) said _{Al X Ga 1-X} N _Al provided on the epitaxial film Y _{Ga 1-Y} N epitaxial layer (0 ≦ Y <1, Y <X).

Because this epitaxial _substrate, comprising a heterojunction between Al _{X Ga 1-X} N is provided on the N surface of the substrate _{Al X Ga 1-X} N epitaxial layer and _Al Y _{Ga 1-Y} N epitaxial film, the hetero The two-dimensional electron gas contributes to conduction without the formation of the two-dimensional hole gas at the junction interface. Therefore, this epitaxial substrate is suitable for a transistor that operates using a two-dimensional electron gas instead of a two-dimensional hole gas.

In the epitaxial substrate according to still another aspect of the present invention, the thickness of the Al _X Ga _1-X N epitaxial layer is preferably 50 nm or more. According to this epitaxial substrate, if the thickness of the Al _X Ga _1-X N epitaxial layer is 50 nm or more, Al _X Ga _1-X N with good crystal quality can be formed.

In the epitaxial substrate according to still another aspect of the present invention, the thickness of the Al _Y Ga _1-Y N epitaxial layer is preferably 1 nm or more and 100 nm or less. According to this epitaxial substrate, since the thickness of the Al _Y Ga _1-Y N epitaxial layer is 1 nm or more, a two-dimensional electron gas having a sufficient density for the field effect transistor is accumulated. Moreover, if the thickness of the Al _Y Ga _1-Y N epitaxial layer is 100 nm or less, Al _Y Ga _1-Y N having good crystal quality can be formed on the Al _X Ga _1-X N for the field effect transistor. .

In the epitaxial substrate according to still another aspect of the present invention, the Al _X Ga _1-X N substrate may be an AlN substrate, and the Al _X Ga _1-X N epitaxial film may be an AlN epitaxial film. Since the epitaxial substrate includes a heterojunction of an AlN film and an Al _Y Ga _1-Y N film provided on an AlN substrate having an N surface on the main surface, the epitaxial substrate operates using only the conduction of a two-dimensional electron gas. An epitaxial substrate suitable for a transistor is provided.

In the epitaxial substrate according to still another aspect of the present invention, the Al _Y Ga _1-Y N epitaxial film is preferably a GaN epitaxial film. Since this epitaxial substrate includes a heterojunction between an AlN film and a GaN film provided on the N surface of the AlN substrate, it is suitable for a transistor that operates using a two-dimensional electron gas instead of a two-dimensional hole gas. .

  In the epitaxial substrate according to still another aspect of the present invention, the thickness of the AlN epitaxial film is preferably 50 nm or more. According to this epitaxial substrate, if the thickness of the AlN epitaxial layer is 50 nm or more, it is possible to form AlN with good crystal quality.

  In the epitaxial substrate according to still another aspect of the present invention, the GaN epitaxial film preferably has a thickness of 1 nm or more and 100 nm or less. According to this epitaxial substrate, since the thickness of the GaN epitaxial layer is 1 nm or more, a two-dimensional electron gas having a sufficient density for the field effect transistor is accumulated. Moreover, if the thickness of the GaN epitaxial layer is 100 nm or less, GaN having good crystal quality can be formed on the AlN layer for the field effect transistor.

In the epitaxial substrate according to still another aspect of the present invention, the main surface of the Al _X Ga _1-X N substrate has one or a plurality of areas, and at least one of the areas includes the Al _X The N face of the Ga _1-X N substrate may appear.

  The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

  As described above, according to the present invention, a field effect transistor having a structure capable of avoiding electrical conduction of a two-dimensional hole gas and made of a nitride material of a Wruzite structure, and the field effect transistor. An epitaxial substrate is provided.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown as examples. Subsequently, embodiments of the field effect transistor and the epitaxial substrate according to the present invention will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

(First embodiment)
FIG. 1 is a drawing showing a field effect transistor according to the present embodiment. The field effect transistor 11 includes an AlN support base 13, an AlN epitaxial layer 15, a GaN epitaxial layer 17, and a gate electrode 19. The AlN support base 13 is made of a crystal having a Wruzite structure and is a conductive or insulating support. The AlN epitaxial layer 15 is provided on the N-plane area of the AlN support base 13. The GaN epitaxial layer 17 is provided on the AlN epitaxial layer 15.

  Since the heterojunction 21 of the AlN epitaxial layer 15 and the GaN epitaxial layer 17 provided on the N surface of the AlN support base 13 is included, a two-dimensional hole gas is not formed at the interface of the heterojunction 21, and the transistor Eleven conduction is provided through the two-dimensional electron gas 23.

  The gate electrode 19 is provided on the GaN epitaxial layer 17 and is Schottky bonded to the GaN epitaxial layer 17. The gate electrode 19 controls the conduction of the two-dimensional electron gas 23. A current controlled by the gate electrode 19 flows through the source electrode 25 and the drain electrode 27. As already described, the AlN epitaxial layer 15 is provided on the N-plane area of the main surface 13a of the AlN support base 13, and therefore, the surface 15a of the AlN epitaxial layer 15 has an N-face on the AlN support base 13. The N plane appears corresponding to the area. The GaN epitaxial layer 17 is provided on the AlN epitaxial layer 15, and therefore, an N plane appears on the surface 17 a of the GaN epitaxial layer 17 corresponding to the N plane area of the AlN epitaxial layer 15.

  Since AlN has high thermal conductivity, the transistor 11 is excellent in heat dissipation. The GaN epitaxial layer 17 is, for example, undoped. The AlN epitaxial layer 15 is preferably undoped, for example, but may contain an n-type dopant. The band gap of gallium nitride in the GaN epitaxial layer 17 is smaller than the band gap of aluminum nitride in the AlN epitaxial layer 15. The two-dimensional electron gas 23 is accumulated on the GaN epitaxial layer side at the interface between the GaN epitaxial layer 17 and the AlN epitaxial layer 15 and travels in the GaN epitaxial layer 17. Since the band gap of gallium nitride is smaller than that of aluminum nitride, the source electrode 25 and the drain electrode 27 are preferably joined to the GaN epitaxial layer 17.

In the field effect transistor 11, if the thickness D1 of the AlN epitaxial layer 15 is 50 nm or more, AlN having good crystal quality can be formed. Moreover, if the thickness D1 of the AlN epitaxial layer 15 is 100 μm or less, it is practical and AlN with good crystal quality can be formed. Further, in the field effect transistor 11, if the thickness D2 of the Al _Y Ga ₁ -YN epitaxial layer 17 is 1 nm or more, a two-dimensional electron gas having a sufficient density is accumulated. Moreover, if the thickness D2 of the Al _Y Ga _1-Y N epitaxial layer 17 is 100 nm or less, GaN with good crystal quality can be formed on the AlN layer.

Example 1
A field effect transistor having the structure shown in FIG. 2A is formed by the following manufacturing method. An AlN film 33 having a thickness of 0.5 μm is deposited on the N surface of the AlN substrate 31 having a Wruzite structure. A 30 nm thick GaN film 35 is deposited on the AlN film 33. These epitaxial growths are performed using a low pressure MOCVD apparatus. As a raw material, for example, TMAl, TMG, and NH ₃ can be used. In this example, both layers are undoped. A source electrode 37a and a drain electrode 37b made of Ti / Al / Ti / Au are formed on the GaN film. Next, a gate electrode 37c made of Au is produced. The gate length is 2 μm, for example.

On the other hand, a field effect transistor having the structure shown in FIG. 2B is formed. An AlN film 43 having a thickness of 0.5 μm is deposited on the Al surface of the AlN substrate 41 having a Wruzite structure. A GaN film 45 having a thickness of 100 nm is deposited on the AlN film 43. On the GaN film 45, an Al _0.2 Ga _0.8 N film 47 having a thickness of 30 nm is deposited. These epitaxial growths are performed using a low pressure MOCVD apparatus. As a raw material, for example, TMAl, TMG, and NH ₃ can be used. In this example, both layers are undoped. A source electrode 49a and a drain electrode 49b made of Ti / Al / Ti / Au are formed on the AlGaN film. Next, a gate electrode 49c made of Au is produced. The gate length is 2 μm, for example.

  FIG. 3A is a diagram showing current characteristics A of the field effect transistor having the structure shown in FIG. FIG. 3B is a drawing showing current characteristics B of the field effect transistor having the structure shown in FIG. The horizontal axis indicates the source-drain voltage, and the vertical axis indicates the drain current. In each of FIGS. 3A and 3B, several IV characteristics are depicted depending on the gate voltage. Comparing the current characteristic A with the current characteristic B, when the gate voltage is deep (large on the negative side) and the source-drain voltage is large in the characteristic B, the transistor is sufficiently turned off depending on the gate bias as compared with the characteristic A. Is not done. Therefore, it is understood that the current characteristic A of the field effect transistor is excellent in the pinch-off characteristic.

Since the transistor having this structure has a structure (AlN / GaN structure) including a plurality of epitaxial layers grown on the N-plane of the AlN substrate having a Wruzite structure, a high-quality crystal is grown on the AlN substrate. . In addition, since AlN in the AlN / GaN structure is homojunction on the N surface of the AlN substrate, the AlN homoepitaxial layer is composed of crystals of good quality with few crystal defects. As a result, the GaN layer grown on the AlN homoepitaxial layer also consists of a good quality crystal with few crystal defects. As a result, an excellent quality AlN / GaN heterojunction is formed. In addition, since this heterojunction is formed on the N surface of the AlN substrate, a two-dimensional electron gas that effectively contributes to conduction is formed at the AlN / GaN interface and a two-dimensional hole gas is not formed. Transistor operation becomes possible. That is, if a sapphire substrate or the like is used, an excellent structure as in this embodiment cannot be realized. Furthermore, heterojunctions in this embodiment since it is AlN / GaN structure, the conduction band energy difference at the hetero interface △ E _C is increased, allowing excellent transistor operation of leakage current less pinch-off characteristics.

(Second Embodiment)
FIG. 4 is a diagram showing a field effect transistor according to the present embodiment. The field effect transistor 51 includes an AlN support base 53, an AlN epitaxial layer 55, an Al _Y Ga _1-Y N epitaxial layer (0 <Y <1) 57, and a gate electrode 59. The AlN support base 53 is made of a crystal having a Wruzite structure and is a conductive or insulating support. The AlN epitaxial layer 55 is provided on the N-plane area of the AlN support base 53. The Al _Y Ga _1-Y N epitaxial layer 57 is provided on the AlN epitaxial layer 55.

Since the heterojunction 61 of the AlN epitaxial layer 55 and the Al _Y Ga _1-Y N epitaxial layer 57 provided on the N surface of the AlN support base 53 is included, the transistor 51 is formed without forming a two-dimensional hole gas. Is provided via the two-dimensional electron gas 63 at the interface of the heterojunction 61.

The gate electrode 59 _is provided on the Al Y _{Ga 1-Y} N epitaxial layer 57, and Schottky junction to the _Al Y _{Ga 1-Y} N epitaxial layer 57. The gate electrode 59 controls the conduction of the two-dimensional electron gas 63. A current controlled by the gate electrode 59 flows through the source electrode 65 and the drain electrode 67. As already described, the AlN epitaxial layer 55 is provided on the N-plane area of the main surface 53a of the AlN support base 53. Therefore, the surface 55a of the AlN epitaxial layer 55 is provided on the N face of the AlN support base 53. The N plane appears corresponding to the area. Further, the Al _Y Ga _1-Y N epitaxial layer 57 is provided on the AlN epitaxial layer 55, and therefore, the surface 57 a of the Al _Y Ga _1-Y N epitaxial layer 57 has an N surface of the AlN epitaxial layer 55. The N plane appears corresponding to the area.

The Al _Y Ga _1-Y N epitaxial layer 57 is, for example, undoped. The AlN epitaxial layer 55 is preferably undoped, for example, but may contain an n-type dopant. The band gap of the Al _Y Ga _1-Y N epitaxial layer 57 is smaller than the band gap of the AlN epitaxial layer 55. Two-dimensional electron gas 63 _is stored in the _Al Y _{Ga 1-Y} N epitaxial layer side of the interface of the Al Y _{Ga 1-Y} N epitaxial layer 57 and the AlN epitaxial layer _55, the Al Y _{Ga 1-Y} N epitaxial layer 57 Drive on. Since the band gap of Al _Y Ga _1-Y N is smaller than that of AlN, the source electrode 65 and the drain electrode 67 are preferably joined to the Al _Y Ga _1-Y N epitaxial layer 57. Preferably, the range of the aluminum composition of Al _Y Ga _1-Y N is 0 or more and 0.9 or less. By setting the composition difference with the AlN epitaxial layer 55 to about 0.1 or more, a sufficient two-dimensional electron gas concentration and conduction band energy difference ΔE _C can be obtained, the leakage current is reduced and the pinch-off characteristics are improved. .

In the field effect transistor 51, if the thickness D3 of the AlN epitaxial layer 55 is 50 nm or more, AlN having good crystal quality can be formed. Further, if the thickness D3 of the AlN epitaxial layer 55 is 100 μm or less, it is practical and AlN having a good crystal quality can be formed. Further, in the field effect transistor 51, since the thickness D4 of the Al _Y Ga _1-Y N epitaxial layer 57 is 1 nm or more, a two-dimensional electron gas having a sufficient density is accumulated. Also, if the thickness D4 of the Al _Y Ga _1-Y N epitaxial layer 57 is 50 nm or less, Al _Y Ga _1-Y N with good crystal quality can be formed on the AlN layer.

(Example 2)
A field effect transistor having the structure shown in FIG. 2A is formed by the following manufacturing method. An AlN film having a thickness of 0.5 μm is deposited on the N surface of an AlN substrate having a Wruzite structure. A 30 nm thick Al _0.25 Ga _0.75 N film is deposited on the AlN film. These epitaxial growths are performed using a low pressure MOCVD apparatus. As a raw material, for example, TMAl, TMG, and NH ₃ can be used. In this example, both layers are undoped. A source electrode and a drain electrode made of Ti / Al / Ti / Au are formed on Al _0.25 Ga _0.75 N. Next, a gate electrode made of Au is produced. The gate length is 2 μm, for example.

As described above, the transistor of this structure has a structure (AlN / Al _Y Ga _1-Y N structure) including a plurality of epitaxial layers grown on the N surface of the AlN substrate having a Wruzite structure. A good quality crystal is grown on the AlN substrate. Further, since AlN in the AlN / Al _Y Ga _1-Y N structure forms a homojunction on the N surface of the AlN substrate, this AlN homoepitaxial layer is composed of crystals of good quality with few crystal defects. As a result, _{Al Y Ga 1-Y} N layers forming the heterojunction AlN homoepitaxial layer may also consist of less good quality crystal crystal defects. As a result, excellent _{AlN / Al Y Ga 1-Y} N heterojunction quality is formed. In addition, since this heterojunction is formed on the N surface of the AlN substrate, a two-dimensional electron gas that effectively contributes to conduction is formed at the AlN / Al _Y Ga _1-Y N interface and a two-dimensional hole gas is formed. Since it is not formed, high-performance transistor operation becomes possible. Similar to the first embodiment, if a sapphire substrate or the like is used, an excellent structure as in the present embodiment cannot be realized.

(Third embodiment)
FIG. 5 is a diagram showing a field effect transistor according to the present embodiment. The field effect transistor 71 includes an Al _X Ga _1-X N support base (0 <X <1) 73, an Al _X Ga _1-X N epitaxial layer 75, and an Al _Y Ga _1-Y N epitaxial layer (0 ≦ Y <1, Y <X) 77 and a gate electrode 79. The Al _X Ga _1-X N support base 73 is made of a crystal having a Wruzite structure and is a conductive or insulating support. The Al _X Ga _1-X N epitaxial layer 75 is provided on the N-plane area of the Al _X Ga _1-X N support base 73. The Al _Y Ga _1-Y N epitaxial layer 77 is provided on the Al _X Ga _1-X N epitaxial layer 75.

Since including the _{Al X Ga 1-X N Al} X Ga 1-X N epitaxial layer 75 and the _Al Y _{Ga 1-Y} N heterojunction 81 between the epitaxial layer 77 provided on the N surface of the support base 73, the electric field The conduction of the transistor 71 is provided through the two-dimensional electron gas 83 at the interface of the heterojunction 81 without the formation of a two-dimensional hole gas in the effect transistor.

The gate electrode 79 _is provided on the Al Y _{Ga 1-Y} N epitaxial layer 77, and Schottky junction to the _Al Y _{Ga 1-Y} N epitaxial layer 77. The gate electrode 79 controls the conduction of the two-dimensional electron gas 83. A current controlled by the gate electrode 79 flows through the source electrode 85 and the drain electrode 87. As already described, the Al _X Ga _1-X N epitaxial layer 75 is provided on the N-plane area of the main surface 73a of the Al _X Ga _1-X N support base 73, and therefore, Al _X Ga _{1- 1 On} the surface 75 a of the _X N epitaxial layer 75, an N plane appears corresponding to the N plane area of the Al _X Ga _1-X N support base 73. Further, the Al _Y Ga _1-Y N epitaxial layer 77 is provided on the Al _X Ga _1-X N epitaxial layer 75, and therefore, the surface 77 a of the GaN epitaxial layer 77 has Al _X Ga _1-X N An N plane appears corresponding to the N plane area of the epitaxial layer 75.

The Al _Y Ga _1-Y N epitaxial layer 77 is undoped, for example. The Al _X Ga _1-X N epitaxial layer 75 is preferably undoped, for example, and may contain an n-type dopant. The band gap of Al _Y Ga _1-Y N (Al _Y Ga _1-Y N epitaxial layer 77) is smaller than the band gap of Al _X Ga _1-X N (Al _X Ga _1-X N epitaxial layer 75). Two-dimensional electron gas 83 _is stored in the _Al Y _{Ga 1-Y} N epitaxial layer side of the interface of the Al Y _{Ga 1-Y} N epitaxial layer 77 and the _{Al X Ga 1-X} N epitaxial layer _75, Al Y _{Ga 1- It} travels in the YN epitaxial layer 77. Since the band gap of Al _Y Ga _1-Y N is smaller than that of Al _X Ga _1-X N, the source electrode 85 and the drain electrode 87 are preferably joined to the Al _Y Ga _1-Y N epitaxial layer 77. .

In the field effect transistor _71, if the Al _{X Ga 1-X} N thickness D5 of the epitaxial layer 75 is 50nm or more, it can be formed of AlGaN good crystal quality. If the thickness D5 of the Al _X Ga _1-X N epitaxial layer 75 is 100 μm or less, it is practical and AlGaN with good crystal quality can be formed. In the field effect transistor 71, since the thickness D6 of the Al _Y Ga _1-Y N epitaxial layer 77 is 1 nm or more, a two-dimensional electron gas having a sufficient density is accumulated. In addition, if the thickness D6 of the Al _Y Ga _1-Y N epitaxial layer 77 is 100 nm or less, Al _Y Ga _1-Y N having good crystal quality can be formed on the Al _X Ga _1-X N layer.

Example 3
The field effect transistor according to this embodiment is formed by the following manufacturing method. An Al _0.5 Ga _0.5 N film having a thickness of _0.5 μm is deposited on the N surface of an Al _0.5 Ga _0.5 N substrate having a Wruzite structure. A 30 nm thick Al _0.2 Ga _0.8 N film is deposited on the Al _0.5 Ga _0.5 N film. These epitaxial growths are performed using a low pressure MOCVD apparatus. As the raw material, for example, TMAl, TMG, NH ₃ ) can be used. In this example, both layers are undoped. A source electrode and a drain electrode made of Ti / Al / Ti / Au are formed on the Al _0.2 Ga _0.8 N film. Next, a gate electrode made of Au is produced. The gate length is 2 μm, for example.

Example 4
A field effect transistor is formed by the following manufacturing method. An Al _0.5 Ga _0.5 N film having a thickness of _0.5 μm is deposited on the N surface of an Al _0.5 Ga _0.5 N substrate having a Wruzite structure. A GaN film having a thickness of 30 nm is deposited on the Al _0.5 Ga _0.5 N film. These epitaxial growths are performed using a low pressure MOCVD apparatus. As a raw material, for example, TMAl, TMG, and NH ₃ can be used. In this example, both layers are undoped. A source electrode and a drain electrode made of Ti / Al / Ti / Au are formed on the GaN film. Next, a gate electrode made of Au is produced. The gate length is 2 μm, for example.

As described above, the transistor of this structure has a structure including a plurality of epitaxial layers (Al _X Ga _1-X N / Al _Y Ga Ga) grown on the N surface of an Al _X Ga _1-X N substrate having a Wruzite structure. _{Since it has a 1-YN} structure, 0 ≦ X <Y <1), a high-quality crystal is grown on the AlGaN substrate. _{Also, Al X Ga 1-X} N of the _{Al X Ga 1-X N /} Al Y Ga 1-Y N _structure, since the homozygous on N surface of the Al _{X Ga 1-X} N substrate, the The Al _X Ga _1-X N homoepitaxial layer consists of a good quality crystal with few crystal defects. As a _{result, Al Y Ga 1-Y} N layers forming the heterojunction Al _{X Ga 1-X} N homoepitaxial layers may also consist of less good quality crystal crystal defects. As a result, an excellent quality Al _X Ga _1-X N / Al _Y Ga _1-Y N heterojunction is formed. Moreover, since this heterojunction is formed on the N surface of the Al _X Ga _1-X N substrate, the two-dimensional electron gas that effectively contributes to conduction is Al _X Ga _1-X N / Al _Y Ga _1-Y N. Since it is formed at the interface and no two-dimensional hole gas is formed, high-performance transistor operation is possible. Similar to the first embodiment, if a sapphire substrate or the like is used, an excellent structure as in the present embodiment cannot be realized.

In this embodiment, since the heterojunction has an Al _X Ga _1-X N / Al _Y Ga _1-Y N structure (0 <Y <1), preferably, Al _Y Ga _1-Y N and Al _X Ga ₁ the difference in the aluminum composition between _-X N (Y-X) is about 0.1. A sufficient two-dimensional electron gas concentration and conduction band energy difference ΔE _C are obtained by setting the composition difference between the Al _Y Ga _1-Y N epitaxial layer and the Al _X Ga _1-X N epitaxial layer to about 0.1 or more. Leakage current is reduced, and pinch-off characteristics are improved. Therefore, the range of the aluminum composition of Al _X Ga _1-X N is preferably 0.1 or more. Moreover, the range of the aluminum composition of Al _X Ga _1-X N is preferably about 1 or less. Further, the range of the aluminum composition of Al _Y Ga _1-Y N is preferably 0 or more. Furthermore, the range of the aluminum composition of Al _Y Ga _1-Y N is preferably about 0.9 or less.

Preferably, the range of the aluminum composition of Al _X Ga _1-X N is about 0.1 or less.

  In the first to third embodiments, in the field effect transistors 11, 51, 71, the source electrode material preferably includes at least one of Ti, Al, Au, Pt, Pd, and Mo. The material of the drain electrode preferably contains at least one of Ti, Al, Au, Pt, Pd, and Mo. According to the material of the source electrode and the drain electrode, a low resistance junction is provided for the gallium nitride material. In the field effect transistors 11, 51, 71, the material of the gate electrode preferably includes at least one of Ni, Au, Pt, and Pd. When these gate electrode materials are used, a good Schottky junction is provided for a gallium nitride-based material.

As described above, the field effect transistors according to the first to third embodiments include the Al _X Ga _1-X N support base (0 <X ≦ 1), the Al _X Ga _1-X N epitaxial layer, , Al _Y Ga _1-Y N epitaxial layer (0 ≦ Y <1, Y <X), a gate electrode, a source electrode, and a drain electrode. The Al _X Ga _1-X N support substrate has a Wruzite structure. Part or all of the main surface of the Al _X Ga _1-X N support base is an N plane. The Al _X Ga _1-X N epitaxial layer is provided on the N-plane area of the Al _X Ga _1-X N support base. The Al _Y Ga _1-Y N epitaxial layer is provided on the Al _X Ga _1-X N epitaxial layer. Since the heterojunction of the Al _X Ga _1-X N epitaxial layer and the Al _Y Ga _1-Y N epitaxial layer provided on the N surface of the Al _X Ga _1-X N support base is included, the field effect transistor has a two-dimensional structure. Without the formation of hole gas, the transistor conducts through the two-dimensional electron gas at the interface of the heterojunction. Moreover, it is preferable to provide the area | region containing an n-type dopant immediately under the source electrode and drain electrode of the field effect transistor which concerns on the 1st-3rd embodiment.

(Fourth embodiment)
FIG. 6A shows an epitaxial substrate for a group III nitride field effect transistor. The epitaxial substrate 91 includes a Wruzite Al _X Ga _1-X N substrate (0 <X ≦ 1) 93, an Al _X Ga _1-X N epitaxial film 95, and an Al _Y Ga _1-Y N epitaxial film (0 ≦ _X ). Y <1, Y <X) 97.
The Al _X Ga _1-X N epitaxial film 95 is provided on the N surface of the Al _X Ga _1-X N substrate 93. The Al _Y Ga _1-Y N epitaxial film 97 is provided on the Al _X Ga _1-X N epitaxial film 95.

Because this epitaxial _substrate, comprising a heterojunction between Al _{X Ga 1-X} N is provided on the N surface of the substrate _{Al X Ga 1-X} N epitaxial layer and _Al Y _{Ga 1-Y} N epitaxial layer, two-dimensional A two-dimensional electron gas at the interface of the heterojunction is formed without forming a hole gas. Preferred semiconductor combinations are
Al _X Ga _1-X N substrate 93, Al _X Ga _1-X N film 95, Al _Y Ga _1-Y N film 97
AlN, AlN, GaN
AlN, AlN, AlGaN
AlGaN, AlGaN, GaN
_{Al X Ga 1-X N,} Al X Ga 1-X N, Al Y Ga 1-Y N (X> Y)
It is.

The thickness of Al _X Ga _1-X N thickness of the epitaxial layer 95 and the _Al Y _{Ga 1-Y} N epitaxial layer 97, is already suitable range used for transistors in the first to third embodiments.

FIGS. 6B and 6C are diagrams illustrating a method of manufacturing an epitaxial substrate for a group III nitride field effect transistor. As shown in FIG. 6B, an Al _X Ga _1-X N substrate (0 <X ≦ 1) 93 having a Wruzite structure is prepared. An N plane appears on part or all of the main surface 93 a of the Al _X Ga _1-X N substrate 93. As shown in FIG. 6C, an Al _X Ga _1-X N film 95 is epitaxially grown on the main surface 93 a of the Al _X Ga _1-X N substrate 93. The thickness of the Al _X Ga _1-X N epitaxial layer 95 is, for example, 50 nm to 100 μm. Since the Al _X Ga _1-X N film 95 forms a homojunction with the Al _X Ga _1-X N substrate 93, the crystal quality of the Al _X Ga _1-X N film 95 is excellent. On the main surface 95 a of the Al _X Ga _1-X N film 95, an N surface appears corresponding to the N surface area of the main surface 93 a of the Al _X Ga _1-X N substrate 93. As shown in FIG. 6D, an Al _Y Ga _1-Y N film 97 is epitaxially grown on the main surface 95a of the Al _X Ga _1-X N film 95. The thickness of the Al _Y Ga _1-Y N film 97 is, for example, 1 nm or more, and at most about 100 nm. The Al _Y Ga _1-Y N film 97 forms a heterojunction with the Al _X Ga _1-X N film 95. Since the crystal is grown on the Al _X Ga ₁ -XN film 95 having excellent crystal quality, the crystal quality of the Al _Y Ga ₁ -YN film 97 is excellent. On the main surface 97 a of the Al _Y Ga _1-Y N film 97, an N surface appears corresponding to the N surface area of the main surface 93 a of the Al _X Ga _1-X N substrate 93. The epitaxial growth can be performed by, for example, a low pressure MOCVD method.

  As described above, according to the present embodiment described as an example of the present invention, even if a highly polarized Wruzite structure nitride-based material is used, the electric conductivity of the two-dimensional hole gas is increased in the high electron mobility transistor. Conduction can be avoided.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

FIG. 1 shows a field effect transistor according to a first embodiment. FIG. 2A shows a field effect transistor including an epitaxial layer provided on the N surface of an AlN substrate. FIG. 2B shows a field effect transistor including an epitaxial layer provided on the Al surface of the AlN substrate. FIG. 3A is a diagram showing current characteristics A of the field effect transistor having the structure shown in FIG. FIG. 3B is a drawing showing current characteristics B of the field effect transistor having the structure shown in FIG. FIG. 4 shows a field effect transistor according to the second embodiment. FIG. 5 shows a field effect transistor according to the third embodiment. FIG. 6A shows an epitaxial substrate for a group III nitride field effect transistor. 6 (B), 6 (C), and 6 (D) are diagrams illustrating a method of manufacturing an epitaxial substrate for a group III nitride field effect transistor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Field effect transistor, 13 ... AlN support base, 15 ... AlN epitaxial layer, 17 ... GaN epitaxial layer, 19 ... Gate electrode, 21 ... Heterojunction, 23 ... Two-dimensional electron gas, 25 ... Source electrode, 27 ... Drain electrode , 51 ... FET, 53 ... AlN support base, 55 ... AlN epitaxial _{layer, 57 ... Al Y Ga 1-} Y N epitaxial layer, 59 ... gate electrode, 61 ... heterozygous, 63 ... two-dimensional electron gas, 65 ... source electrode, 67 ... drain electrode, 71 ... _{FET, 73 ... Al X Ga 1-} X N supporting _{substrate, 75 ... Al X Ga 1-} X N epitaxial _{layer, 77 ... Al Y Ga 1-} Y N epitaxial layer, 79 ... gate electrode, 91 ... epitaxial _{substrate, 93 ... Al X Ga 1-} X N substrate, 95 ... A _X Ga _1-X N epitaxial _{layer, 97 ... Al Y Ga 1-} Y N epitaxial layer

Claims (15)

A field effect transistor,
Al _X Ga _1-X N supporting substrate (0 <X ≦ 1) having a Wruzite structure;
An Al _X Ga _1-X N epitaxial layer provided on the N surface of the Al _X Ga _1-X N support base;
An Al _Y Ga _1-Y N epitaxial layer (0 <Y <1, Y <X) provided on the Al _X Ga _1-X N epitaxial layer;
A gate electrode forming a Schottky junction with the Al _Y Ga _1-Y N epitaxial layer;
A source electrode provided on the Al _Y Ga _1-Y N epitaxial layer;
A drain electrode provided on the Al _Y Ga _1-Y N epitaxial layer,
The field effect transistor is a high electron mobility transistor;
The field effect transistor, wherein the Al _X Ga _1-X N epitaxial layer and the Al _Y Ga _1-Y N epitaxial layer form a heterojunction. 2. The field effect transistor according to claim 1, wherein the thickness of the Al _X Ga _1-X N epitaxial layer is 50 nm or more. 3. The field effect transistor according to claim 1, wherein a thickness of the Al _Y Ga _1-Y N epitaxial layer is 1 nm or more and 100 nm or less. A field effect transistor,
An AlN support substrate having a Wruzite structure;
An AlN epitaxial layer provided on the N surface of the AlN support substrate;
An Al _Y Ga _1-Y N epitaxial layer (0 <Y <1) provided on the AlN epitaxial layer;
A gate electrode forming a Schottky junction with the Al _Y Ga _1-Y N epitaxial layer;
A source electrode provided on the Al _Y Ga _1-Y N epitaxial layer;
A drain electrode provided on the Al _Y Ga _1-Y N epitaxial layer,
The field effect transistor is a high electron mobility transistor;
A field effect transistor, wherein the AlN epitaxial layer and the Al _Y Ga _1-Y N epitaxial layer form a heterojunction.   The field effect transistor according to claim 4, wherein the thickness of the AlN epitaxial layer is 50 nm or more. 6. The field effect transistor according to claim 4, wherein the Al _Y Ga _1-Y N epitaxial layer has a thickness of 1 nm or more and 50 nm or less. 4. The field effect transistor according to claim 1, wherein the Al _X Ga _1-X N support base forms a homojunction with the Al _X Ga _1-X N epitaxial layer. 5. .   The field effect transistor according to any one of claims 4 to 6, wherein the AlN support substrate forms a homojunction with the AlN epitaxial layer. The material of the source electrode includes at least one of Ti, Al, Au, Pt, Pd, and Mo.
The field effect transistor according to any one of claims 1 to 8, wherein the material of the drain electrode includes at least one of Ti, Al, Au, Pt, Pd, and Mo.   10. The field effect transistor according to claim 1, wherein the material of the gate electrode includes at least one of Ni, Au, Pt, and Pd. 11. An epitaxial substrate,
Al _X Ga _1-X N substrate (0 <X ≦ 1) having a Wruzite structure;
A _{Al X Ga 1-X} N epitaxial layer provided on the N surface of the _{Al X Ga 1-X} N substrate,
An Al _Y Ga _1-Y N epitaxial layer (0 <Y <1, Y <X) provided on the Al _X Ga _1-X N epitaxial layer,
The epitaxial layer characterized in that the Al _X Ga _1-X N epitaxial layer and the Al _Y Ga _1-Y N epitaxial layer form a heterojunction to form a two-dimensional electron gas of a high electron mobility transistor. substrate. 12. The epitaxial substrate according to claim 11, wherein a thickness of the Al _X Ga _1-X N epitaxial layer (0 <X ≦ 1) is 50 nm or more and 100 μm or less. The epitaxial substrate according to claim 11 or 12, wherein a thickness of the Al _Y Ga _1-Y N epitaxial layer is 1 nm or more and 100 nm or less. The Al _X Ga _1-X N substrate is an AlN substrate,
The epitaxial substrate according to claim 13, wherein the Al _X Ga _1-X N epitaxial layer is an AlN epitaxial layer.   The epitaxial substrate according to claim 14, wherein the thickness of the AlN epitaxial layer is 50 nm or more.

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