Nitride semiconductor device

Abstract

A nitride semiconductor device includes: a first semiconductor layer made of first nitride semiconductor; a second semiconductor layer formed on a principal surface of the first semiconductor layer and made of second nitride semiconductor having a bandgap wider than that of the first nitride semiconductor; a control layer selectively formed on, or above, an upper portion of the second semiconductor layer and made of third nitride semiconductor having a p-type conductivity; source and drain electrodes formed on the second semiconductor layer at respective sides of the control layer; a gate electrode formed on the control layer; and a fourth semiconductor layer formed on a surface of the first semiconductor layer opposite to the principal surface, having a potential barrier in a valence band with respect to the first nitride semiconductor and made of fourth nitride semiconductor containing aluminum.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a nitride semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a graph showing a relationship between the Al content x of an undoped Al_xGa_1-xN underlying layer and the maximum current value in the nitride semiconductor device of the first embodiment.

FIG. 3 is a cross-sectional view illustrating a nitride semiconductor device according to a second embodiment of the present invention.

FIG. 4 is a graph showing a relationship between the In content y of an undoped In_yGa_1-yN layer and the maximum current value in the nitride semiconductor device of the second embodiment.

FIG. 5 is a cross-sectional view illustrating a nitride semiconductor device according to a third embodiment of the present invention.

FIG. 6 is a graph showing a relationship between an undoped GaN layer and the switching speed in the nitride semiconductor device of the third embodiment.

FIG. 7 is a cross-sectional view illustrating a conventional nitride semiconductor FET.

FIG. 8 is a diagram showing distributions of fixed charge and free electrons generated by polarization in the conventional nitride semiconductor FET.

FIG. 9 is a diagram showing an energy band of the conventional nitride semiconductor FET.

FIG. 10 is a graph showing drain current-drain voltage characteristics of the conventional nitride semiconductor FET.

FIG. 11 is a cross-sectional view illustrating a nitride semiconductor device as a comparative example.

Claims

1. A nitride semiconductor device, comprising: a first semiconductor layer made of first nitride semiconductor;a second semiconductor layer formed on a principal surface of the first semiconductor layer and made of second nitride semiconductor having a bandgap wider than that of the first nitride semiconductor;a control layer selectively formed on, or above, an upper portion of the second semiconductor layer and made of third nitride semiconductor having a p-type conductivity;source and drain electrodes formed on the second semiconductor layer at respective sides of the control layer;a gate electrode formed on the control layer; anda fourth semiconductor layer formed on a surface of the first semiconductor layer opposite to the principal surface, having a potential barrier in a valence band with respect to the first nitride semiconductor and made of fourth nitride semiconductor containing aluminum.

2. The nitride semiconductor device of claim 1, wherein upon application of a forward bias to the gate electrode, holes are injected into a channel region formed in the first semiconductor layer and the control layer controls electrical conductivity between the source electrode and the drain electrode.

3. The nitride semiconductor device of claim 1, wherein the fourth semiconductor layer has an aluminum content in the range from 0.03 to 0.1, both inclusive.

4. The nitride semiconductor device of claim 1, wherein the first nitride semiconductor contains indium.

5. The nitride semiconductor device of claim 1, wherein the first semiconductor layer has a thickness larger than 0 nm and equal to or smaller than 30 nm.

6. The nitride semiconductor device of claim 3, wherein the first nitride semiconductor contains indium, and the first semiconductor layer has a thickness larger than 0 nm and equal to or smaller than 30 nm.