AIN Insulator for III-V MIS Applications

Abstract

Abstract : The use of AIN as an insulator for GaAs MIS structures was investigated. The AIN films were prepared by reactive evaporation in an ultra-high vacuum system. Aluminum from a MBE source was reacted with NH3 from an effusion cell on a heated GaAs substrate. Several material preparation variables were investigated which included choice of substrate, substrate surface preparation, growth temperature, Al/NH3 flux ratio, and deposition rate. The optimum AIN film growth parameters in terms of morphology and adhesion were found to involve use of thermally cleaned GaAs substrates, a 500-550 C substrate growth temperature, an effective NH3 partial pressure of 0.00005 to 0.00001 Torr at the GaAs surface, and a growth rate of about 100A/min. The AIN prepared in this manner was stoichiometric, polycrystalline, had the hexagonal wurtzite structure, and had no detectable oxygen or carbon contamination as determined by x-ray diffraction, TEM far infrared transmission, and in situ Auger electron spectroscopy. The insulating properties of the AIN/GaAs MIS structures appeared to depend on preparation conditions. It was concluded from several studies that small amounts of undetectable residual oxygen contamination were most likely responsible for the observed variation in AIN conductivity. Complex C-V results were obtained for most AIN/GaAs MIS structures which most likely were influenced by large interface state densities, leakage, and charge storage effects. No definitive correlation between AIN/GaAs preparation parameters and interface state charge densities was obtained. Processes were developed to fabricate both gated diodes and MISFET's from AIN/GaAs samples.