Calcia-stabilized zirconia thin films in GaAs metal/insulator/semiconductor technology: Reduction of GaAs native oxide

Abstract

The interface between GaAs and its native oxide is thermodynamically unstable and introduces many defects, which are mainly responsible for the poor electrical properties of this material. We propose in this paper an original way of reducing the native oxide layer and then obtaining a thermodynamically stable and abrupt interface between GaAs and a deposited dielectric. It is shown that these conditions are well fulfilled by layers of calcia-stabilized zirconia (CSZ), which is well known as a solid electrolyte. CSZ is a good insulator at moderate temperatures and allows the reduction of the native oxide at high temperatures. Thermodynamic analysis of the GaAs oxide and of the CSZ solid solution show that, in an H 2 atmosphere containing 20 ppm of water, the GaAs oxide is reduced at an annealing temperature T⩾500 °C, whereas the CSZ solid solution is stable up to T=2200 °C. Our aim in this paper was to study the mechanisms of native oxide reduction at 550 °C⩽ T⩽800 °C through a thin layer of CSZ. Nuclear microanalysis, Rutherford backscattering in random and channelling geometry and ion scattering spectrometry were used to measure the oxygen losses during the annealing treatment and to study the gallium and arsenic epitaxial regrowth. It was found that the native oxide reduction takes place even in the case of intentional preformation of a relatively thick (approximately 250 Å) GaAs anodic oxide layer. The gallium and arsenic atoms liberated by oxide reduction are epitaxially regrown on the underlying substrate and a good and relatively abrupt interface is observed between the GaAs and the CSZ deposited layers. Preliminary electrical measurements seem to indicate that an inversion layer can be obtained, although hysteresis and frequency dispersion do occur in the capacitance-voltage curves, as commonly observed.