Metal-semiconductor technology for Ni/Au-Ge on n-GaAs

The results of a detailed electrical and metallurgical study are presented for an Ohmic contact which is used in GaAs device technology. The electrical behavior of alloyed Ni/Au-Ge films on epitaxial n-type GaAs found from conventional current-voltage and capacitance-voltage techniques is correlated to the composition-depth profiles found using a new thin-film analysis technique combining Auger electron spectrsocopy with sputter etching. Below the eutectic temperature of the Au-Ge mixture, the Ni is shown to diffuse rapidly through the Au-Ge film. Above the Au-Ge eutectic temperature, the specific contact resistance is shown to drop by a factor of greater than 10⁹as the Ge and Au diffuse into the GaAs. The presence of the Ni at the Au-Ge/GaAs interface is shown to markedly alter the resulting contact surface uniformity. The lack of a reproducible and reliable Ohmic contact to moderately doped n-type GaAs has been a persistent problem in metal-semiconductor technology. One widely used technique is to alloy evaporated metal layers, such as Ni/Au-Ge, to clean GaAs in order to obtain a low resistance contact (1-3). We report here a detail electrical and metallurgical study of the Ni/Au-Ge contact system on epitaxial GaAs; unique to our study is the new metallurgical technique of thin-film profiling using Auger electron spectroscopy and sputter etching. This work is an extension of the preliminary metallurgical results reported earlier on bulk material only (4).