Contact mechanisms and design principles for alloyed Ohmic contacts to p-type GaN

Abstract

Contact mechanisms and design principles of alloyed Ohmic contacts to p-type GaN (p-GaN) are studied. Illustrative studies include bilayer, trilayer and quadrilayer Ohmic contacts. Almost all contacts appear to follow the proposed design principles. The removal of the surface insulating layer, preferably by plasma etching, leads to metal/semiconductor barrier lowering. This, together with thermionic emission, plays a crucial role for yielding low-resistance metal/p-GaN contacts. Band-gap narrowing and/or image force lowering due to heavy doping also contribute to the low contact resistivity. A judicious choice of the layer thicknesses of appropriate metal combination, rapid thermal annealing (RTA) time, RTA temperature and RTA ambient can produce large-work-function alloy(s) in contact with the p-GaN epitaxial layer, creating a robust low-resistivity thermionic-emission-induced Ohmic contact. The fundamental physics of contact mechanisms and design principles proposed in the study is useful for making other contacts. These are general enough to be extended to other III–V nitride materials, at the least.

Acknowledgements

The work is dedicated to two of the author's finest teachers, Mr Nagendranath Das and (the late) Professor H. N. Bose. The author wishes to thank his graduate students, postdoctoral fellows and collaborators for help and suggestions. He is especially grateful to Mr Abhishek Motayed, Mrs Dong Feng Wang, Mr Zhifang Fan and Mr Changzhi Lu. He appreciates illuminating discussions with Dr Albert Davydov, Dr Wallace T. Anderson, Professor Hadis Morkoç and Dr Kenneth A. Jones. S.N.M. was a Summer Faculty Fellow, Electronic Science and Technology Divison, US Naval Research Laboratory, Washington, DC, USA where much of the research for this paper was carried out. The research was supported by the US Air Force Office of Scientific Research, National Aeronautics and Space Administration Goddard Space Flight Center, Greenbelt, Maryland, US Army Research Laboratory, Adephi, Maryland, and US Ballistic Missiles Defense Organization.

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Additional information

Notes on contributors

S. Noor Mohammad †

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