# US 8,772,786 B2 · Gallium nitride devices having low ohmic contact resistance

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- Number: US 8,772,786 B2
- Document ID: US8772786B2
- Status: Granted
- Kind: B2
- Application number: 13/548,305
- Filed: 2012-07-13
- Published: 2014-01-16
- Granted: 2014-07-08
- Earliest claimed: 2012-07-13
- Assignees: Raytheon Company
- Applicants: Kamal Tabatabaie; William E. Hoke; Eduardo M. Chumbes; Kevin McCarthy
- Inventors: Kamal Tabatabaie; William E. Hoke; Eduardo M. Chumbes; Kevin McCarthy
- Web page: https://patentgrep.com/patent/US8772786B2

## CPC

- H10D 30/015: {of FETs having heterojunction interface channels or heterojunction gate electrodes, e.g. HEMT}
- H10D 30/4755: {having wide bandgap charge-carrier supplying layers, e.g. modulation doped HEMTs such as n-AlGaAs/GaAs HEMTs}
- H10D 30/478: {the 2D charge carrier gas being at least partially not parallel to a main surface of the semiconductor body}
- H10D 62/117: {Shapes of semiconductor bodies}
- H10D 62/149: {Source or drain regions of field-effect devices}
- H10D 62/852: being Group III-V materials comprising three or more elements, e.g. AlGaN or InAsSbP
- H10D 62/8503: {Nitride Group III-V materials, e.g. AlN or GaN}
- H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES

## Abstract

A semiconductor structure having mesa structure comprising: a lower semiconductor layer; an upper semiconductor layer having a higher band gap than, and in direct contact with, the lower semiconductor layer to form a two-dimension electron gas (2DEG) region between the upper semiconductor layer. The 2DEG region has outer edges terminating at sidewalls of the mesa. An additional electron donor layer has a band gap higher than the band gap of the lower layer disposed on sidewall portions of the mesa structure and on the region of the 2DEG region terminating at sidewalls of the mesa. An ohmic contact material is disposed on the electron donor layer. In effect, a sideway HEMT is formed with the electron donor layer, the 2DEG region and the ohmic contact material increasing the concentration of electrons (i.e., lowering ohmic contact résistance) all along the contact between the lower semiconductor layer and the electron donor layer.

## Claims

### Claim 1

A semiconductor structure, comprising:
a substrate;
a mesa structure disposed on a surface of the substrate, the mesa structure having slopped sidewalls oblique to the surface of the substrate, comprising:
an electron donor layer disposed on, and along, the sloped sidewall of the mesa structure;
a lower semiconductor layer having ends of an upper portion terminating at a lower portion of the electron donor layer;
an upper semiconductor layer having ends terminating at an upper portion of the electron donor layer, having a different band gap from, and in direct contact with, the lower semiconductor layer;
wherein a two-dimension electron gas region is formed having one portion disposed along a bottom portion of the upper semiconductor layer and another portion disposed along lower portions of the electron donor layer;
an ohmic contact material disposed on the electron donor layer;
wherein the upper semiconductor layer includes AlN;
wherein the lower semiconductor layer is GaN; and
wherein the electron donor layer is n-type doped AlGaN.

### Claim 2 (depends on 1)

The semiconductor structure recited in claim 1 wherein the ohmic contact material is n-type doped GaN.

### Claim 3 (depends on 2)

The semiconductor structure recited in claim 2 including a gate electrode in Schottky contact with the upper semiconductor layer.

### Claim 4 (depends on 3)

The semiconductor structure recited in claim 3 including an ohmic contact in contact with the ohmic contact material.