Heterojunction field effect transistor

• US 6,064,082 A
• Filed: 05/29/1998
• Issued: 05/16/2000
• Est. Priority Date: 05/30/1997
• Status: Expired due to Term

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Imanaga, Shunji, Kobayashi, Toshimasa, Kawai, Hiroji
• Primary Examiner(s): Meier, Stephen D.
• Application Number:
  US09/086,988
• Time in Patent Office: 718 Days
• Field of Search: 257/192, 257/191
• US Class Current: 257/192
• CPC Class Codes: H01L 29/2003 Nitride compounds
• CPC Class Codes: H01L 29/7783 using III-V semiconductor material

Abstract

A heterojunction field effect transistor realizing a high performance by a significant decrease. in source resistance while maintaining a sufficiently high gate resistivity to voltage is provided. Sequentially stacked on a c-face sapphire substrate via a buffer layer are an undoped GaN layer, undoped Al₀.3 Ga₀₇ N layer, undoped GaN channel layer, undoped Al₀.15 Ga₀.85 N spacer layer, n-type Al₀.15 Ga₀.85 N electron supply layer, graded undoped Al_z Ga_1-z N barrier layer and n-type Al₀.06 Ga₀.94 N contact layer, and a gate electrode, source electrode and drain electrode are formed on the n-type Al₀.06 Ga₀.94 N contact layer to form a AlGaN/GaN HEMT. The Al composition z in the graded undoped Al_z Ga_1-z N barrier layer continuously decreases from 0.15 to 0.06, for example, from the n-type Al₀.15 Ga₀.85 N electron supply layer toward the n-type Al₀.06 Ga₀.94 N contact layer. An n⁺⁺ -type GaN contact layer may be formed on the n-type Al₀.06 Ga₀.94 N contact layer in the region for the source electrode and the drain electrode, and the source electrode and the drain may be formed on it.

Claims

1. A heterojunction field effect transistor comprising:

an electron moving layer;

an electron supply layer on said electron moving layer;

a barrier layer on said electron supply layer; and

a contact layer on said barrier layer, a source electrode on said contact layer, wherein the bottom energy of the conduction band of said barrier layer immediately under said source electrode being decreased continuously from said electron supply layer toward said contact layer.

2. The heterojunction field effect transistor according to claim 1 wherein the bottom energy of the conduction band of said barrier layer is approximately equal to the bottom energy of the conduction band of said contact layer along the interface between said barrier layer and said contact layer.

3. The heterojunction field effect transistor according to claim 1 wherein the energy gap of said barrier layer immediately under said source electrode continuously decreases from said electron supply layer toward said contact layer.

4. The heterojunction field effect transistor according to claim 1 wherein the composition of said barrier layer continuously varies from said electron supply layer toward said contact layer to continuously decreases the bottom energy of the conduction band of said barrier layer from said electron supply layer toward said contact layer.

5. The heterojunction field effect transistor according to claim 1 wherein said barrier layer is undoped.

6. The heterojunction field effect transistor according to claim 1 wherein said contact layer is n-type.

7. The heterojunction field effect transistor according to claim 1 wherein said electron moving layer is made of Ga_1-x In_x N (where 0≦

x≦

1), said electron supply layer is made of Al_y Ga_1-y N (where 0≦

y≦

1), said barrier layer is made of Al_z Ga_1-z N, and said contact layer is made of n-type Al_u Ga_1-u N (where 0≦

u≦

0.1) or n-type Ga_1-v In_v N (where 0≦

v≦

1).

8. The heterojunction field effect transistor according to claim 7 wherein the Al composition z in said Al_z Ga_1-z N forming said barrier layer continuously decreases from y to u from said electron supply layer toward said contact layer.

9. The heterojunction field effect transistor according to claim 7 wherein the Al composition z in said Al_z Ga_1-z N forming said barrier layer is not less than 0.1 along the interface between said barrier layer and said contact layer.