Semiconductor device using a group III nitride-based semiconductor

1. A semiconductor device using a group III nitride-based semiconductor,

wherein

the semiconductor device comprises a double heterostructure which is constructed by sequentially laminating an Al x Ga 1-x N lower barrier layer composed of lattice-relaxed Al x Ga 1-x N (0<x<1), an In y Ga 1-y N channel layer composed of In y Ga 1-y N (0≦y≦1) with compressive strain and an Al z Ga 1-z N contact layer composed of Al z Ga 1-z N (0<z≦1),

wherein

the composition of the Al x Ga 1-x N lower barrier layer is constant,

an Al composition (z) of the Al z Ga 1-z N contact layer is selected in the range of 0.05≦z≦0.5,

the semiconductor device comprises a buffer layer made of Al u Ga 1-u N (0≦u≦1), in which an Al composition (u) is matched to an Al composition (x) of the Al x Ga 1-x N lower barrier layer at the interface with the Al x Ga 1-x N lower barrier layer,

the Al composition (z) of the Al z Ga 1-z N contact layer is larger than the Al composition (x) of the Al x Ga 1-x N lower barrier layer (z>x),

a two-dimensional electron gas is produced in the vicinity of an interface of the In y Ga 1-y N channel layer with the Al z Ga 1-z N contact layer,

at least two ohmic electrodes are formed as a source electrode and a drain electrode on the Al z Ga 1-z N contact layer,

a gate electrode is provided in a region located between the source electrode and the drain electrode, and thereby, the semiconductor device comprises a structure composed of the gate electrode, the source electrode and the drain electrode, which constitute a field effect transistor,

a recessed portion is provided in a region located between the source electrode and the drain electrode by removing a part of said Al z Ga 1-z N contact layer by etching it away until said In y Ga 1-y N channel layer is exposed,

said gate electrode is formed so as to be embedded in the recessed portion with intervention of an insulating film that is formed in the shape of single layer made of a polycrystalline or amorphous insulating substance, or in the shape of multiple layers, each layer of which is made of a polycrystalline or amorphous insulating substance, and

the semiconductor device is a metal-insulator-semiconductor (MIS)-type field effect transistor, in which electrons are accumulated in a channel region at the interface between the insulating film and the In y Ga 1-y N channel layer at the ON state of the MIS-type field effect transistor.

2. The semiconductor device according to claim 1 ,

wherein

said insulating film is a single layer film made of a polycrystalline or amorphous insulating material, which is selected from the group consisting of Si 3 N 4 , SiO 2 , SiON, Al 2 O 3 , Ga 2 O 3 , ZnO, MgO and HfO 2 , or a multilayer film comprising a laminated structure that is composed of a plurality of layers, each layer of which is made of a polycrystalline or amorphous insulating material selected from the group consisting of Si 3 N 4 , SiO 2 , SiON, Al 2 O 3 , Ga 2 O 3 , ZnO, MgO and HfO 2 .

3. The semiconductor device according to claim 1 ,

wherein

said Al x Ga 1-x N lower barrier layer is doped with a shallow n-type impurity, and

when said gate electrode, said source electrode and said drain electrode are set at an equal potential, then a two-dimensional electron gas is produced in the vicinity of an interface between said In y Ga 1-y N channel layer and said Al x Ga 1-x N lower barrier layer.

4. The semiconductor device according to claim 1 ,

wherein

the Al composition (z) of said Al z Ga 1-z N contact layer and the Al composition (x) of said Al x Ga 1-x N lower barrier layer are selected so that a difference (z−x) between them satisfies the condition (z−x)>0.02.

5. The semiconductor device according to claim 1 ,

wherein

said Al z Ga 1-z N contact layer is doped with a shallow n-type impurity.

6. The semiconductor device according to claim 1 ,

wherein

said In y Ga 1-y N channel layer is made of In y Ga 1-y N (0≦y≦1) which is undoped, or doped with a shallow n-type impurity.

7. The semiconductor device according to claim 1 ,

wherein

each of said Al x Ga 1-x N lower barrier layer, said In y Ga 1-y N channel layer and said Al z Ga 1-z N contact layer is an epitaxial film grown by C-axis growth.

8. The semiconductor device according to claim 1 ,

wherein

band discontinuity ΔEc (Al z Ga 1-z N/In y Ga 1-y N) due to a conduction band energy difference between said Al z Ga 1-z N and said In y Ga 1-y N at a heterojunction interface between said Al z Ga 1-z N contact layer and said In y Ga 1-y N channel layer is selected within the range of equal to or larger than 50 meV.

9. The semiconductor device according to claim 1 ,

wherein

band discontinuity ΔEc (Al x Ga 1-x N/In y Ga 1-y N) due to a conduction band energy difference between said Al x Ga 1-x N and said In y Ga 1-y N at a heterojunction interface between said Al x Ga 1-x N lower barrier layer and said In y Ga 1-y N channel layer is selected within the range of equal to or larger than 50 meV.

10. The semiconductor device according to claim 1 ,

wherein

said Al x Ga 1-x N lower barrier layer is formed on the buffer layer made of Al u Ga 1-u N (0<u≦1) grown by C-axis growth, which is formed on a substrate.

11. The semiconductor device according to claim 1 ,

wherein

a film thickness of said insulating film is selected within the range of 5 nm-500 nm.

12. The semiconductor device according to claim 1 ,

wherein

said Al x Ga 1-x N lower barrier layer is doped with a shallow n-type impurity at sheet density Nd,

negative polarization charges due to spontaneous polarization effect and piezo polarization effect are produced at sheet density Np at the interface between said Al x Ga 1-x N lower barrier layer and said In y Ga 1-y N channel layer, and

said sheet density Nd and said sheet density Np satisfy the following relational equation therebetween; Nd≦Np.