JP2001160656A - Nitride compound semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride compound semiconductor device which can improve electrical characteristics, while suppressing carrier scattering. SOLUTION: GaN having crystal of a wurtzite structure is selected as a substrate material 1. Nitride semiconductor layers 2, 3, 4, 5 are laminated on a surface (a) (1,1,-2,0) of the substrate material, which is a substrate surface 1a. The source-drain direction, which serves as an electrical path, is rendered parallel with the direction of an axis (c) of the crystal which constitutes the laminated nitride semiconductor layers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride-based compound having a wurtzite crystal structure and a nitride-based compound semiconductor laminated on a specific surface of the substrate material to suppress carrier scattering and improve electrical characteristics. The present invention relates to a compound semiconductor device.

[0002]

2. Description of the Related Art Conventionally, a c-plane of hexagonal SiC and a c-plane of sapphire indicated by (0,0,0,1) in FIG. Have been. This is because a nitride-based compound semiconductor having a wurtzite structure can easily grow with c-axis orientation, and thus has an advantage that a film having more excellent crystallinity can be obtained on a c-plane substrate.
On the other hand, as a laser using a nitride-based compound semiconductor, JP-A-7-297495 and JP-A-10-41547.
Nos. 1 and 2 are known, and these laser semiconductors are used to obtain a cavity surface using cleaving property of a c-plane.
The a-plane (see (1,1, -2,0) in FIG. 3) is used for the laminated surface of the substrate.

[0003]

A conventional light emitting diode (L) in which a nitride-based compound semiconductor is laminated on a c-plane substrate 21.
ED) or a laser diode (LD), as shown by the arrow in FIG. 4, flows a current parallel to the c-axis [S. Nakamu
ra et. al, Jpn. J. Appl. Phys. 34 (1995) L797, 35
(1996) L74], the effect of carrier scattering due to dislocations D present in the crystal is small, and the emission characteristics are hardly deteriorated. However, a heterostructure field effect transistor (HFET) formed by laminating a nitride-based semiconductor on a c-plane substrate 22
As shown in FIG. 5, dislocations D arranged perpendicular to the substrate surface are
Since the structure is orthogonal to the current path between the source 23 and the drain 24 indicated by the arrow, carriers are remarkably scattered by the dislocations D, and as a result, there is a problem that electrical characteristics are deteriorated.

Accordingly, an object of the present invention is to select a specific surface of a material having a crystal having a wurtzite structure as a substrate surface and to laminate a nitride-based compound semiconductor on this surface, thereby suppressing carrier scattering and providing electrical characteristics. An object of the present invention is to provide a nitride-based compound semiconductor device capable of improving characteristics.

[0005]

Means for Solving the Problems The present inventors have focused on the fact that the device characteristics are dramatically improved by a laminated structure in which dislocations run parallel to the current path, and the surface of the substrate on which such a laminated structure is obtained is considered. As a result of intensive studies to find a surface index, the present invention having the following configuration has been achieved. That is, the invention of claim 1 is a nitride-based compound semiconductor device using a nitride-based compound semiconductor, wherein a material having a wurtzite structure crystal has a (1,1, -2,0) plane (a-plane). ) Or (1, -1,0,0) plane (m
Surface) as a substrate, and the direction in which current flows is parallel to the c-axis direction.

In the nitride-based compound semiconductor device of the first aspect, the nitride-based compound semiconductor stacked on the substrate surface having the specific plane index has a dislocation in which the c-axis of the crystal is parallel to the substrate surface. Run parallel to the substrate surface. And
In this nitride-based compound semiconductor device, a current flows in the c-axis direction, that is, in parallel to the substrate surface, so that scattering of carriers is reduced and a semiconductor device having excellent electrical characteristics is realized.

According to a second aspect of the present invention, there is provided a nitride-based compound semiconductor device.
This is a field-effect transistor using a flute mouth structure, in which a source-drain direction is parallel to a c-axis direction. In the nitride-based compound semiconductor device according to claim 2, the direction of the source-drain, which is the current path, is:
Since it is parallel to the c-axis, which is the direction in which dislocations travel in the stacked nitride-based compound semiconductor, carrier scattering is reduced and a field-effect transistor with excellent electrical characteristics is realized.

According to a third aspect of the present invention, there is provided a nitride-based compound semiconductor device.
The substrate material having the wurtzite structure crystal is GaN, Al
It is characterized by being one of N, SiC and ZnO. The substrate material of the nitride-based compound semiconductor device according to claim 3, which is a stable hexagonal crystal and can reduce lattice mismatch with the nitride-based compound semiconductor to be laminated, so that the nitride-based compound semiconductor having excellent crystallinity is obtained. Can grow.

The nitride-based compound semiconductor device of claim 4 is
The substrate material having the crystal having the wurtzite structure is an off-substrate having an inclination angle of 5 degrees or less. In the nitride-based compound semiconductor device according to claim 4, since the substrate surface is inclined within 5 degrees with respect to the a-plane or the m-plane, there are many steps on the substrate surface that serve as crystal growth starting points, A nitride-based compound semiconductor having excellent crystallinity can be more stably grown on the a-plane or m-plane having excellent crystallinity.

According to a fifth aspect of the present invention, there is provided a nitride-based compound semiconductor device.
The substrate material having the crystal having the wurtzite structure is SiC, and has a buffer layer of AlN. It belongs to a hexagonal system and has a unit cell of 4H (ABCBA). On a surface which is an a-plane or an m-plane of 4H-SiC as a wurtzite structure substrate material, for example, as a nitride compound without a buffer layer, When GaN is directly grown, an AB stack of hexagonal 2H and a face-centered cubic 3 are stacked in a 4H-SiC stack (ABCBA).
2H (ABAB) and 3C (ABC)
ABC) is formed, and stacking faults are formed at the interface in a direction perpendicular to the substrate surface, that is, for example, in a direction perpendicular to the current path of the field effect transistor, so that the stacking faults cause significant scattering of carriers. Will be.
However, in the nitride-based compound semiconductor device according to claim 5, since AlN having a stable 2H structure is used as the buffer layer, 2H-GaN (hexagonal GaN) or the like having no stacking faults on the buffer layer is stable. Accordingly, a nitride-based compound semiconductor device having excellent transport characteristics in which carrier scattering due to stacking faults does not occur can be realized.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. (Example 1) FIG. 1 shows a first example of a nitride-based compound semiconductor device.
Heterostructure field effect transistor (H
FIG. 2 is a cross-sectional view showing an outline of the FET. In FIG. 1, 1
Is a substrate made of GaN whose surface 1a is an a-plane having an index of (1,1, -2,0) in the hexagonal plane index system of FIG. 3, and 2 is a carrier concentration of 5 × 10 ¹⁶ cm ^-3, an undoped GaN layer laminated in a thickness of 2 [mu] m, 3 is a spacer layer of undoped Al _0.2 Ga _0.8 N was stacked in a film thickness 10nm on the surface of the GaN layer 2, 4 on the surface of the spacer layer 3 N-type Al _0.2 Ga laminated at a carrier concentration of 2 × 10 ¹⁸ cm ^-3 and a thickness of 30 nm
_0.8 donor layer of N, n-type GaN cap layer laminated on the surface on both sides of the donor layer 4 is 5, 6 were formed on the surface of the donor layer 4 is removed the center cap layer 5 by etching with Cl ₂ Pt The gate electrode 7 of / Au is a source / drain electrode of Ti / Al formed on the surface of the cap layer 5 on both sides.

Each of the above layers is formed by metal organic chemical vapor deposition (MOV).
PE: Metal Organic Vapor Phase Epitaxy) and molecular beam epitaxy (MBE: Molecular Beam Epitaxy)
And the like can be used as a crystal growth method. In the first embodiment, the MOVPE method is used. That is, first, the surface of the substrate 1 was cleaned at a substrate temperature of 1000 ° C. for 10 minutes in a nitrogen atmosphere. Next, after growing the GaN layer 2 while keeping the substrate temperature as it is, raising the substrate temperature to 1100 ° C., growing the spacer layer 3 and the donor layer 4 of Al _0.2 Ga _0.8 N, and again 1000 ° C. A GaN cap layer 5 was grown at a substrate temperature of.

The thus manufactured HFET shown in FIG.
Is that the c-axis of the crystal constituting each nitride layer laminated on the substrate 1 is parallel to the surface of the substrate 1, and the dislocations in this crystal also extend mainly along the c-axis, that is, parallel to the substrate surface. Since this direction coincides with the source-drain direction which is the current path of the HFET, carrier scattering is reduced, and a heterostructure field effect transistor having excellent electrical characteristics can be obtained. Further, in Example 1, the material of the substrate 1 having the crystal having the wurtzite structure is a stable hexagonal crystal,
GaN that can reduce lattice mismatch with the nitride layer to be laminated
Is used, a heterostructure field-effect transistor having a stack with excellent crystallinity can be obtained. As such a stable hexagonal substrate material, in addition to GaN, AlN, Si, etc.
C, ZnO can also be used. As the surface of the substrate 1, instead of the a-plane having a plane index of (1,1, -2,0),
Even if an m-plane (see FIG. 3) having a plane index of (1, -1,0,0) is selected, the c-axis of the crystal constituting each nitride layer laminated on this substrate is parallel to the substrate surface. Thus, a heterostructure field effect transistor having excellent electric characteristics can be obtained.

As an example of the first embodiment, the gate length is 1 μm.
An HFET having a distance of 5 μm and a source-drain distance of 5 μm was fabricated, and its characteristics were compared with those of a conventional HFET. As a result, the HFET according to the first embodiment has a maximum oscillation frequency of fmax = 20 GHz and a transconductance g _m = 1 at room temperature.
It was 80 mS / mm. On the other hand, in a conventional HFET having the same structure and the source / drain direction perpendicular to the c-axis,
At room temperature, the maximum oscillation frequency is fmax = 15 GHz, the transconductance g _m = 140 mS / mm,
It has been clarified that the influence of carrier scattering is large in the conventional HFET in which the current path is orthogonal to the direction in which the dislocation runs.

(Embodiment 2) The HFET of Embodiment 2 is shown in FIG.
In place of the GaN substrate 1 having an index of (1,1, -2,0), as shown by a broken line in FIG. It has the same structure as the HFET of the first embodiment described with reference to FIG. 1 except that a GaN substrate 1 having 'a' is used. G
The crystal growth method of each layer laminated on the aN substrate 1 'is the same as described in the first embodiment.

Therefore, the HFET of the second embodiment is different from the HFET of the first embodiment.
In addition to having the same function and effect as described above, since the substrate surface 1′a is inclined by 2 ° with respect to the a-plane, a micro step (step) serving as a crystal growth starting point along the substrate surface 1 ′ Can be formed, and crystals can be grown smoothly and uniformly, so that each nitride layer having excellent crystallinity can be grown more stably. Even if a surface inclined by 2 ° with respect to the m-plane (see FIG. 3) having a plane index of (1, -1,0,0) is obtained as the surface of the substrate 1 ′, the same operation and effect can be obtained. Can be. Further, the inclination of the substrate surface with respect to the a-plane or the m-plane is 2
The angle can be set to not more than 5 °.

As an example of the second embodiment, an HF having a gate length of 1 μm and a source-drain distance of 5 μm as in the first embodiment.
ET was manufactured and its characteristics were compared with those of a conventional HFET. As a result, it was found that the HFET according to Example 2 had a maximum oscillation frequency of fmax = 25 GHz and a transconductance g _m = 200 mS / mm at room temperature, and had better electrical characteristics than Example 1.

(Embodiment 3) FIG. 2 is a sectional view showing an outline of an HFET according to a third embodiment of the present invention. In FIG. 2, reference numeral 11 denotes a hexagonal plane index of the surface 11a of FIG.
A substrate made of 6H (ABCACB) SiC, which is an m-plane having an index of (0,0); 12 is a buffer layer made of undoped AlN laminated on the surface of the substrate 11 to a thickness of 10 nm;
Is an undoped GaN layer laminated on the surface of the buffer layer 12 to a thickness of 20 nm; 14 is an undoped Al _0.2 Ga _0.8 N spacer layer laminated on the surface of the GaN layer 13 to a thickness of 20 nm; A donor layer of Al _0.2 Ga _0.8 N doped with Si and having a carrier concentration of 5 × 10 ¹⁸ cm ⁻³ and a thickness of 10 nm is deposited on the surface of the donor layer 14, and a donor layer 15 of 2 nm thickness is deposited on the surface of the donor layer 15. Undoped Al _0.2 Ga _0.8 N
A cap layer 17 made of Pt / Au formed at the center of the surface of the cap layer 16; and a source / drain electrode 18 made of Ti / Al formed on both sides of the surface of the cap layer 16.

For each of the above layers, the MOVPE method, the MBE method or the like can be used as a crystal growth method. In the third embodiment, the RF (Radio Frequency) -MBE method is used. That is, first, the surface of the substrate 11 is heated at 900 ° C. for 20 minutes.
Min thermal cleaning, followed after growing a buffer layer 12 of AlN kept intact substrate temperature, the substrate temperature is lowered to 750 ° C., an undoped GaN layer 13, the undoped Al _0.2 Ga _{0 .8} N A spacer layer 14, a donor layer 15 of Al _0.2 Ga _0.8 N doped with Si, and a cap layer 16 of Al _0.2 Ga _0.8 N undoped are sequentially grown. The raw materials used are Al and Ga solids and nitrogen excited in a plasma state at a high frequency.

The HEFT thus manufactured as shown in FIG. 2 is characterized in that it has an AlN buffer layer 12 on the m-plane surface 11a of the substrate 11 made of 6H SiC. In the conventional HEFT, for example, GaN or the like is laminated as a nitride on the m-plane, which is a 4H SiC substrate surface, without passing through the buffer layer 12. In this case, 4H-SiC
The hexagonal 2H AB laminate and the face-centered cubic 3C ABC laminate are mixed in the ABCA stack, so the surface has 2H (ABAB)
And 3C (ABCABC) GaN are formed, and stacking faults are formed at the interface in a direction perpendicular to the substrate surface, that is, in a direction orthogonal to the current path between the source and the drain of the field effect transistor. Carrier was significantly scattered. However, in the HFET of the third embodiment, since AlN having a stable 2H structure is used as the buffer layer 12, 2H-GaN (hexagonal GaN) or the like free from stacking faults is stably obtained on the buffer layer 12. Can be Therefore, it is possible to manufacture an HFET having excellent transport characteristics in which carrier scattering due to stacking faults does not occur.

As an example of the third embodiment, the gate length is 1 μm.
An HFET with a distance of 5 μm and a source-drain distance of 5 μm was fabricated, and its characteristics were compared with those of a conventional HFET. As a result, the HFET according to the third embodiment has a maximum oscillation frequency fmax = 25 GHz and a transconductance g _m = 250 at room temperature.
mS / mm. On the other hand, in the conventional HFET in which the AlN buffer layer is not stacked, the maximum oscillation frequency fmax = 15 GHz and the transconductance g _m = 140 mS / mm at room temperature. In the conventional HFET, carrier scattering due to stacking faults occurs. It became clear that the influence of was large. In addition, as the surface of the substrate 11, the above (1, -1,
Instead of the m-plane having a plane index of (0,0), an a-plane (see FIG. 3) having a plane index of (1,1, -2,0) can be selected.

[0022]

As is apparent from the above description, claim 1
The invention of (1, 1, -2,
Since the (0) plane (a plane) or (1, -1,0,0) plane (m plane) is used as the substrate and the direction in which the current flows is parallel to the c-axis direction, it is laminated on the substrate. The c-axis of the crystal of the nitride-based compound semiconductor layer becomes parallel to the substrate surface, and the dislocations run parallel to the substrate surface. This direction matches the direction in which current flows, so that carrier scattering is small. As a result, a semiconductor device having excellent electric characteristics can be obtained.

According to a second aspect of the present invention, there is provided a heterostructure field-effect transistor as a nitride-based compound semiconductor device, wherein a source-drain direction is a c-axis in which a dislocation runs in the stacked nitride-based compound semiconductor. , The carrier scattering is reduced and a heterostructure field effect transistor having excellent electrical characteristics is obtained.

According to a third aspect of the present invention, there is provided a nitride-based compound semiconductor device, wherein the substrate material having a crystal having a wurtzite structure is GaN, A
Since any one of lN, SiC, and ZnO is used, these substrate materials are stable hexagonal crystals and can reduce lattice mismatch with the nitride-based compound semiconductor to be laminated. Compound semiconductors can be grown.

According to a fourth aspect of the present invention, there is provided a nitride-based compound semiconductor device comprising an off-substrate in which the surface of the substrate material having the wurtzite structure crystal is inclined within 5 degrees with respect to the a-plane or the m-plane. Since there are many steps on the substrate surface that serve as crystal growth starting points, a nitride-based compound semiconductor having excellent crystallinity can be more stably grown on the a-plane or m-plane having excellent crystallinity. .

According to a fifth aspect of the present invention, there is provided a nitride-based compound semiconductor device.
Since the substrate material having the wurtzite structure crystal is SiC and has a buffer layer of AlN, a buffer layer is formed on the surface that is the a-plane or m-plane of 4H-SiC as the conventional wurtzite structure substrate material. Unlike the case where a nitride-based compound is directly grown without interposition, stacking faults are not formed in a direction perpendicular to the current path, and the 2H structure is stable.
Since 2H-GaN (hexagonal GaN) or the like free of stacking faults can be stably obtained on the 1N buffer layer, it is possible to obtain a nitride-based compound semiconductor device having excellent transport characteristics without carrier scattering due to stacking faults. it can.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an outline of a heterostructure field effect transistor according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing an outline of a heterostructure field effect transistor according to a third embodiment of the present invention.

FIG. 3 is a view showing a plane index of a hexagonal crystal material used as a substrate of a nitride-based compound semiconductor.

FIG. 4 is a cross-sectional view of a conventional light emitting diode or laser diode in which a nitride-based compound semiconductor is stacked on a c-plane substrate.

FIG. 5 is a cross-sectional view of a conventional heterostructure field-effect transistor in which a nitride-based compound semiconductor is stacked on a c-plane substrate.

[Explanation of symbols]

1 GaN substrate 1a Substrate surface which is an a-plane having an index of (1,1, -2,0) 1 'GaN substrate having a 2 ° off surface with respect to a-plane 1'a 2 ° with respect to a-plane Inclined substrate surface 2 Undoped GaN layer 3 Undoped Al _0.2 Ga _0.8 N spacer layer 4 n-type Al _0.2 Ga _0.8 N donor layer 5 n-type GaN cap layer 6 gate electrode 7 source / drain electrode 11 6H-SiC Substrate 11a Substrate surface which is an m-plane having an index of (1, -1,0,0) 12 Buffer layer of undoped AlN 13 Layer of undoped GaN 14 Spacer layer of undoped Al _0.2 Ga _0.8 N 15 Doped with Si Al _0.2 Ga _0.8 N donor layer 16 Undoped Al _0.2 Ga _0.8 N cap layer 17 Gate electrode 18 Source / drain electrode

Continued on the front page (72) Inventor Akira Suzuki 22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka F-term (reference) 5F041 AA21 CA33 CA34 CA40 CA41 5F073 CB02 CB04 CB05 CB07 5F102 GB01 GC01 GD01 GJ02 GJ04 GK04 GL04 GM04 GN04 GQ01 GR01

Claims (5)

[Claims] 1. A nitride compound semiconductor device using a nitride compound semiconductor, wherein a (1,1, -2,0) plane (a plane) of a material having a wurtzite structure crystal is provided.
Alternatively, a nitride-based compound semiconductor device using a (1, -1,0,0) plane (m-plane) as a substrate and a direction in which a current flows is parallel to a c-axis direction. 2. The nitride-based compound semiconductor device is a field-effect transistor using a metal-edge structure, and a source-drain direction is parallel to a c-axis direction. 3. The nitride-based compound semiconductor device according to 1. 3. The nitride-based compound semiconductor device according to claim 1, wherein the substrate material having the wurtzite structure crystal is any one of GaN, AlN, SiC, and ZnO. 4. The nitride-based compound semiconductor device according to claim 3, wherein the substrate material having the wurtzite structure crystal is an off-substrate having an inclination angle of 5 degrees or less. 5. The nitride-based compound semiconductor device according to claim 3, wherein the substrate material having the crystal having the wurtzite structure is SiC and has an AlN buffer layer.