Contact degradation of GaAs transferred electron devices

The migration of contact material into the GaAs devices may degrade the device performance (noise, power output) and can shorten the mean time to failure of operational devices. In order to understand contact degradation the interdiffusion of gold/germanium contacts on gallium arsenide has been studied using Rutherford backscattering, ion microprobe (SIMS) and microbeam techniques. Both the depth profiling and imaging properties of the ion microprobe have been used. The microbeam was used for focused Rutherford backscattering giving a lateral resolution approximately 10 μm. When used in conjunction with angle lapped samples it allows analysis to be conducted to greater depths and hence one may use thicker contact films. The use of these techniques has enabled both the lateral and depth distributions of gold, germanium, gallium and arsenic to be obtained. These distributions have revealed gold and germanium spike formation beneath the contact. The information obtained provides insight into the mechanisms involved in the formation of ohmic contacts to gallium arsenide. The degradation of such contacts as a result of thermal and electrical effects is discussed. (Auth.)