The structure and composition of the recently developed Al-Ni-Ge ohmic contacts to n-GaAs were investigated by transmission electron microscopy combined with secondary ion mass spectroscopy (SIMS) and Auger spectroscopy. The semiconductor/metal-alloy interface of these contacts remain very flat after annealing (500°C, for 1 min - contact resistance 1.4×10−6Ωcm2), in contrast to the widely used Au-Ni-Ge contacts. The metal sequence during deposition is found to be a critical factor in determining the electrical contact properties and the dispersion of the oxide layer on the semiconductor surface after chemical cleaning. Ge doping of the GaAs beneath the contact layer was observed by SIMS, and a tunneling mechanism through the n+GaAs:Ge layer was proposed to explain the ohmic properties of the contacts.

Focused-ion-beam (FIB) technology has been applied during the past decade to a wide variety of device and circuit fabrication procedures. The ability to perform maskless implantation, selective sputtering and deposition, and high resolution lithography with a single system has allowed FIB researchers to explore a large number of unique fabrication processes for silicon, GaAs, and heterojunction devices. Currently, exploratory studies in advanced optoelectronic device fabrication employ the largest number of diverse FIB techniques. In this paper, the major application areas of FIB technology to optoelectronic research are reviewed, and possible uses of ultrasmall (≤500 Å) ion beams in the fabrication of optoelectronic device structures with novel properties are described.