JP2004200711A - Nitride based iii-v compound semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a III-V compound semiconductor device which has a steep interface and excellent property such as mobility. <P>SOLUTION: An AlN epitaxial buffer layer 2, a GaN channel layer 3 which is a first binary compound semiconductor layer and has carrier concentration of 1×10<SP>16</SP>cm<SP>-3</SP>, an AlN improved-barrier-property layer 4 which is a second binary compound semiconductor layer, and an Al<SB>0.2</SB>Ga<SB>0.8</SB>N barrier layer 5 which is a ternary compound semiconductor and has carrier concentration of 2×10<SP>17</SP>cm<SP>-3</SP>are stacked on a crystal face (0001) of a semi-insulating SiC substrate 1 in the above order. Then, a source electrode 6a, a drain electrode 6b and a gate electrode 7 are formed thereon. An AlN improved-hetero-property layer, which is the second binary compound layer having a band gap higher than that of the first compound layer, is interposed between the GaN channel layer 3 which is the first binary compound semiconductor layer and the AlGaN barrier layer 5 which is the ternary compound crystal semiconductor layer. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a nitride III-V compound semiconductor device, and more particularly to a nitride III-V compound semiconductor device having no fluctuation in composition or barrier height at an interface of a heterojunction between a channel layer (electron transit layer) and a barrier layer (barrier layer). The present invention relates to a structure of a III-V compound semiconductor device.

  As a combination of materials in an HFET (Hetero Field Effect Transistor) structure, a material in which GaN is used as a channel layer and AlGaN is used as a barrier layer and a heterojunction of these is most commonly used (for example, Patent Document 1 and Patent Document 1) 2).

U.S. Pat. No. 5,192,987 JP-A-10-189944

  Generally, the junction interface between a binary compound semiconductor composed of two elements (eg, AlN, GaN, InN, etc.) and a binary compound semiconductor different from this binary compound semiconductor depends on the growth conditions, but is steep. Easy interface is easily obtained. On the other hand, when a binary compound semiconductor and a ternary mixed crystal semiconductor (for example, AlGaN, GaInN, AlInN, etc.) composed of three elements are combined and joined, the components of the ternary mixed crystal semiconductor are combined with the components of the binary compound semiconductor. When they overlap (for example, GaN and AlGaN, or GaN and GaInN), a steep interface cannot be obtained. This is because, for example, in a heterojunction of GaN and AlGaN as shown in FIG. 3, the same element (Ga) exists over a boundary between two semiconductors. Therefore, GaN, which should be the channel layer, and GaN in the AlGaN, which is the barrier layer, hinder the formation of a steep interface, adversely affect the characteristics of the heterojunction, and cause problems such as a decrease in mobility.

  An object of the present invention is to provide a nitride III-V compound semiconductor device having a steep interface and having excellent characteristics such as mobility.

  The present invention provides a nitride III-V compound semiconductor device having a heterostructure, wherein a first binary compound semiconductor layer forming a channel layer and a ternary mixed crystal semiconductor layer forming a barrier layer are formed between the first binary compound semiconductor layer and the ternary mixed crystal semiconductor layer forming a barrier layer. A nitride-based III-V compound semiconductor device characterized by interposing a binary compound semiconductor layer of No. 2.

  According to the present invention, at the junction between the binary compound semiconductors, the interface becomes steep as long as there is no atomic diffusion. Therefore, in the nitride III-V compound semiconductor device having the hetero structure, the first layer constituting the channel layer is formed. By interposing the second binary compound semiconductor layer between the binary compound semiconductor layer and the ternary mixed crystal semiconductor layer constituting the barrier layer, the steepness at the interface of the hetero junction is improved.

  Further, when such a structure is applied to a nitride-based semiconductor, the piezo effect at the interface is further increased, and this appears in an AlGaAs / GaAs hetero structure in which the carrier concentration of the two-dimensional electron gas can be further increased. There is no effect, and the electrical characteristics can be further improved.

  Further, the invention is characterized in that a band gap of the second binary compound semiconductor layer is larger than a band gap of the first binary compound semiconductor layer.

  If the band gap of the second binary compound semiconductor layer is smaller than the energy gap of the first binary compound semiconductor layer, the second binary compound semiconductor becomes a new channel layer, and Although the junction interface between the binary compound semiconductor and the ternary mixed crystal semiconductor does not become steep, according to the present invention, the band gap of the second binary compound semiconductor layer is changed to the band gap of the first binary compound semiconductor layer. , The steepness of these bonding interfaces is maintained.

  Also, in the present invention, the first binary compound semiconductor layer is formed of InN, GaN, LaN, CeN, PrN, NdN, PmN, SmN, EuN, GdN, TbN, DyN, HoN, ErN, TmN, YbN, LuN. It is one of them.

  According to the present invention, as the first binary compound semiconductor layer, semiconductors having a band gap of 2 to 3.4 eV, such as InN, GaN, LaN, CeN, PrN, NdN, PmN, SmN, EuN, GdN, TbN, One of DyN, HoN, ErN, TmN, YbN, and LuN can be used. The material to be used is determined depending on the band gap of the ternary mixed crystal semiconductor layer forming the barrier layer.

  Also, in the present invention, the second binary compound semiconductor layer includes AlN, InN, GaN, LaN, CeN, PrN, NdN, PmN, SmN, EuN, GdN, TbN, DyN, HoN, ErN, TmN, YbN, One of LuN.

  According to the present invention, as the second binary compound semiconductor layer, AlN, InN, GaN, LaN, CeN, PrN, NdN, PmN, SmN, EuN, GdN, TbN, DyN, HoN, ErN, TmN, YbN, One of LuN can be used. Further, a material to be used is determined depending on a band gap of the first binary compound semiconductor layer included in the channel layer.

  According to the present invention, in a nitride-based III-V compound semiconductor device having a heterostructure, between a first binary compound semiconductor layer forming a channel layer and a ternary mixed crystal semiconductor layer forming a barrier layer Since the second binary compound semiconductor layer is interposed, the steepness at the interface of the hetero junction is improved.

  In addition, the piezo effect at the interface of the junction is further increased, and the carrier concentration of the two-dimensional electron gas can be further increased.

  Further, according to the present invention, since the band gap of the second binary compound semiconductor layer is larger than the band gap of the first binary compound semiconductor layer, steepness of these junction interfaces is maintained.

  According to the invention, as the first binary compound semiconductor layer, a semiconductor having a band gap of 2 to 3.4 eV, such as InN, GaN, LaN, CeN, PrN, NdN, PmN, SmN, EuN, GdN, and TbN. , DyN, HoN, ErN, TmN, YbN, and LuN. The material to be used is determined depending on the band gap of the ternary mixed crystal semiconductor layer forming the barrier layer.

  According to the invention, as the second binary compound semiconductor layer, AlN, InN, GaN, LaN, CeN, PrN, NdN, PmN, SmN, EuN, GdN, TbN, DyN, HoN, ErN, TmN, YbN , LuN can be used. Further, a material to be used is determined depending on a band gap of the first binary compound semiconductor layer included in the channel layer.

Next, specific embodiments of the present invention will be described with reference to examples, but the present invention is not limited by these examples.
Hereinafter, examples will be described.

(Example 1)
FIG. 1 is a cross-sectional view schematically showing a nitride-based III-V compound semiconductor device 10 according to an embodiment of the present invention. The nitride III-V compound semiconductor device 10 includes an AlN epitaxial buffer layer 2 and a first binary compound semiconductor layer on a (0001) crystal plane of a semi-insulating SiC substrate 1 having a carrier concentration of 1 × 10 ^16. cm ⁻³ GaN channel layer 3, AlN barrier characteristic improving layer 4 as a second binary compound semiconductor layer, Al _0.2 Ga _0.8 N ternary mixed crystal semiconductor layer with a carrier concentration of 2 × 10 ¹⁷ cm ⁻³ A barrier layer 5 is laminated in this order, and a source electrode 6a, a drain electrode 6b, and a gate electrode 7 are formed thereon.

As a crystal growth method for forming such a layer structure, a metal organic chemical vapor deposition method (
Metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy using plasma-excited nitrogen (Radio Frequency-Molecular Beam Epitaxy, RF-MBE or Electron Cyclotron Resonance-MBE, ECR-MBE) can be used.

In the present example, it was manufactured in the following steps by MOCVD.
First, the surface of the semi-insulating SiC substrate 1 was cleaned in a hydrogen atmosphere at a substrate temperature of 1000 ° C. for 10 minutes. Next, an AlN epitaxial buffer layer 2 having a thickness of 20 nm was grown at a substrate temperature of 1100 ° C., and subsequently a GaN channel layer 3 having a thickness of 1 μm was grown at a substrate temperature of 1000 ° C. Thereafter, an AlN barrier property improving layer 4 was grown at a substrate temperature of 1000 ° C. Since the energy band gap of AlN forming the AlN barrier characteristic improving layer 4 has an extremely large band gap of 6.2 eV, if this layer thickness is too large, current injection from the barrier layer to the channel layer will not occur. Inhibited and no longer functions as a heterojunction. In other words, it is necessary to maintain the steepness of the interface while ensuring sufficient carrier transport by the tunnel effect. For this reason, it is preferable that the film thickness of the AlN hetero-characteristic improvement layer 4 be 1 to 4 molecular layers. In the present embodiment, the thickness is set to 2 molecular layers to 5 °. Further, the substrate temperature was raised to 1100 ° C. to grow the Al _0.2 Ga _0.8 N barrier layer 5.

  Thereafter, the source electrode 6a, the drain electrode 6b, and the gate electrode 7 were formed by using the photolithography method, and the nitride III-V compound semiconductor device 10 was manufactured. Further, in order to compare the characteristics of the nitride III-V compound semiconductor device 10 of the present embodiment with the second binary compound semiconductor layer interposed therebetween to the characteristics of the conventional compound semiconductor device, the AlN hetero characteristic improving layer 4 A compound semiconductor device having a structure with no intervening is manufactured by the same process.

  Prior to the measurement of the device characteristics, the electrical characteristics of the semiconductor layer were examined by Hall measurement. Table 1 shows the mobility when the AlN hetero characteristic improving layer 4 is interposed between the GaN channel layer 3 and the AlGaN barrier layer 5 and when it is not interposed.

From Table 1, at 300 K where the measurement temperature is room temperature, the mobility was improved when the AlN hetero characteristic improving layer 4 was interposed as compared with the case where the AlN hetero characteristic improving layer 4 was not interposed. At 77 K, which is the measurement temperature of liquid nitrogen (LN ₂ ), a significant difference in mobility appears, indicating that the AlN hetero-characteristic improving layer 4 has improved the interface characteristics.

Next, an HFET in which the length of the gate electrode 7 was 1 μm and the distance between the source electrode 6a and the drain 6b electrode was 5 μm was fabricated, and the characteristics thereof were evaluated. The oscillation frequency f _max = 25 GHz, the transconductance g _m = 200 mS / mm, and when no transconductance is used, f _max = 20 GHz and g _m = 150 mS / mm.

  As described above, the steepness of the interface can be improved by interposing the second binary compound semiconductor at the heterojunction surface of the first binary compound semiconductor and the ternary mixed crystal semiconductor, and the piezo effect at the interface is further improved. By increasing the size, the carrier concentration of the two-dimensional electron gas can be further increased, so that a nitride III-V compound semiconductor device having excellent electrical characteristics can be realized.

(Example 2)
FIG. 2 is a cross-sectional view schematically showing a nitride-based III-V compound semiconductor device 20 according to another embodiment of the present invention. The nitride III-V compound semiconductor device 20 includes an AlN epitaxial buffer layer 12, a GaN layer 13 having a carrier concentration of 1 × 10 ¹⁶ cm ^{−3 on} a (0001) crystal plane of a semi-insulating SiC substrate 11, A GaN channel layer 14 having a carrier concentration of 5 × 10 ¹⁶ cm ⁻³ , a GaN hetero-characteristic improving layer 15 being a second binary compound semiconductor layer, and a ternary mixed crystal semiconductor layer An Al _0.2 Ga _0.8 N barrier layer 16 having a concentration of 2 × 10 ¹⁷ cm ⁻³ is laminated in this order, and a source electrode 17a, a drain electrode 17b, and a gate electrode 18 are formed thereon.

As a crystal growth method for forming such a layer structure, a metal organic chemical vapor deposition method (
Metal-organic chemical vapor deposition-MOCVD) or molecular beam epitaxy using plasma-excited nitrogen (Radio Frequency-Molecular Beam Epitaxy, RF-MBE or Electron Cyclotron Resonance-MBE, ECR-MBE) can be used.

In the present example, it was manufactured in the following steps by the RF-MBE method.
First, the surface of the semi-insulating SiC substrate 11 was cleaned at a substrate temperature of 1000 ° C. in a vacuum for 10 minutes. Next, a 20 nm thick AlN epitaxial buffer layer 12 was grown at a substrate temperature of 800 ° C., and a 1 μm thick GaN layer 13 was subsequently grown at a substrate temperature of 700 ° C. Thereafter, a GaN channel layer 14, a GaN hetero characteristic improving layer 15, and an Al _0.2 Ga _0.8 N barrier layer 16 having a thickness of 30 nm were continuously grown at a substrate temperature of 700 ° C.

  Thereafter, the source electrode 17a, the drain electrode 17b, and the gate electrode 18 were formed by using photolithography to manufacture the nitride III-V compound semiconductor device 20. Further, in order to compare the characteristics of the nitride III-V compound semiconductor device 20 of the present embodiment with the second binary compound semiconductor layer interposed therebetween to the characteristics of the conventional compound semiconductor device, A compound semiconductor device having a structure with no interposition was manufactured in the same process.

  Prior to the measurement of the device characteristics, the electrical characteristics of the semiconductor layer were examined by Hall measurement. Table 2 shows the mobility when the GaN hetero characteristic improving layer 15 is interposed between the GaN channel layer 14 and the AlGaN barrier layer 16 and when it is not interposed.

From Table 2, at a measurement temperature of 300 K at room temperature, the mobility was improved when the GaN hetero characteristic improving layer 15 was interposed, as compared with the case where the GaN hetero characteristic improving layer 15 was not interposed. At 77 K, which is the measurement temperature of liquid nitrogen (LN ₂ ), a significant difference in the mobility appears, indicating that the GaN hetero-characteristic improving layer 15 has improved the interface characteristics.

Next, an HFET in which the length of the gate electrode 18 was 1 μm and the distance between the source electrode 17a and the drain electrode 17b was 5 μm was produced, and the characteristics thereof were evaluated. As a result, when the GaN hetero characteristic improving layer 15 was interposed, The maximum oscillation frequency f _max = 30 GHz, the transconductance g _m = 250 mS / mm, and when no transconductance is interposed, f _max = 22 GHz and g _m = 180 mS / mm. Thus, the effect of the GaN hetero characteristic improving layer 15 was observed.

  As described above, the steepness of the interface can be improved by interposing the second binary compound semiconductor at the heterojunction surface of the first binary compound semiconductor and the ternary mixed crystal semiconductor, and the piezo effect at the interface is further improved. By increasing the size, the carrier concentration of the two-dimensional electron gas can be further increased, so that a nitride III-V compound semiconductor device having excellent electrical characteristics can be realized.

  In Examples 1 and 2, GaN was used for the first binary compound semiconductor layer. However, depending on the band gap of the ternary mixed crystal semiconductor layer constituting the barrier layer, InN, LaN, CeN, and the like were used. Any of PrN, NdN, PmN, SmN, EuN, GdN, TbN, DyN, HoN, ErN, TmN, YbN, and LuN may be used. In this case, which material is used depends on the magnitude of the band gap of the ternary mixed crystal semiconductor layer forming the barrier layer. In the first and second embodiments, AlN and GaN are used for the second binary compound semiconductor layer. However, GaN, AlN, InN, LaN, CeN, PrN, NdN, PmN, SmN, EuN, GdN, TbN, Any of DyN, HoN, ErN, TmN, YbN, and LuN may be used. In this case, which material is used is determined by the band gap of the first binary compound semiconductor layer forming the channel layer.

The present invention is capable of the following embodiments.
The nitride-based III-V compound semiconductor device, wherein the second binary compound semiconductor layer is AlN having a layer thickness of not less than one molecular layer and not more than four molecular layers.

  When AlN is used for the second binary compound semiconductor layer, AlN has an extremely large band gap of 6.2 eV. If the layer thickness is too large, current injection from the barrier layer to the channel layer is inhibited. , Will not function as a heterostructure. By using AlN having a thickness of at least one molecular layer and at most four molecular layers for the second binary compound semiconductor layer, sufficient carrier transport can be performed by the tunnel effect while maintaining the steepness of the junction interface. Therefore, a nitride III-V compound semiconductor device having excellent electric characteristics can be obtained.

FIG. 1 is a cross-sectional view illustrating a structure of a nitride-based III-V semiconductor device 10 according to a first embodiment of the present invention. FIG. 4 is a cross-sectional view illustrating a structure of a nitride-based III-V semiconductor device 20 according to a second embodiment of the present invention. FIG. 3 is a diagram showing a junction interface between a binary compound semiconductor and a ternary mixed crystal semiconductor containing a component of the binary compound semiconductor.

Explanation of reference numerals

Reference Signs List 1,11 Semi-insulating SiC substrate 2,12 AlN epitaxial buffer layer 3,14 GaN channel layer 4 AlN hetero characteristic improving layer 5,16 AlGaN barrier layer 6a, 17a Source electrode 6b, 17b Drain electrode 7,18 Gate electrode 10, Reference Signs List 20 nitride-based III-V compound semiconductor device 13 GaN layer 15 GaN hetero characteristic improving layer

Claims (4)

  In a nitride-based III-V compound semiconductor device having a hetero structure, a second binary compound semiconductor is formed between a first binary compound semiconductor layer forming a channel layer and a ternary mixed crystal semiconductor layer forming a barrier layer. A nitride-based III-V compound semiconductor device, wherein a compound semiconductor layer is interposed.   2. The nitride III-V compound semiconductor device according to claim 1, wherein a band gap of the second binary compound semiconductor layer is larger than a band gap of the first binary compound semiconductor layer.   The first binary compound semiconductor layer is one of InN, GaN, LaN, CeN, PrN, NdN, PmN, SmN, EuN, GdN, TbN, DyN, HoN, ErN, TmN, YbN, LuN. The nitride III-V compound semiconductor device according to claim 1 or 2, wherein:   The second binary compound semiconductor layer is formed of one of AlN, InN, GaN, LaN, CeN, PrN, NdN, PmN, SmN, EuN, GdN, TbN, DyN, HoN, ErN, TmN, YbN, and LuN. The nitride-based III-V compound semiconductor device according to claim 1, wherein:

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