Very low resistance non-alloyed ohmic contacts using as-rich GaAs

Abstract

Ohmic contacts with low specific contact resistivity are essential for contemporary electronic devices such as HBTs, lasers, LEDs, and MESFETs. Alloyed Au-Ge-Ni contacts for nGaAs and alloyed Au-Zn contacts for p-GaAs have been widely used in GaAs semiconductor devices, but alloyed contacts produce a rough interface with the semiconductor and hence, are not good optical reflectors. Devices like light emitting diodes, vertical cavity surface-emitting lasers, and solar cells, need ohrmc contacts that are also good optical reflectors. Optimizing the reflectivity and the resistivity of the back contact to such devices poses a considerable challenge. We have developed a new technology for forming non-alloyed ohmic contacts to nand p-GaAs using Asrich layers. As-rich GaAs epi layers can be produced by molecular beam epitaxy (MBE) using lower than normal growth temperatures. Due to the amphoteric nature of Si, the typical dopant for n-GaAs, achieving high n-type doping concentrations is difficult. Simple reaction kinetics show that N+/ Np x n?/n2.