The effects of oxidation and hydrogen annealing on the silicon-sapphire-interface region of SOS

Aluminum-sapphire-silicon capacitor structures were fabricated from n-SOS and p-SOS epitaxially deposited layers. The modified MIS capacitance method was used to characterize the Si-sapphire interface region electrically and to monitor changes due to exposure of the SOS to 1) oxidation at 900°C in HCl-steam and 2) annealing at 500°C in H2. Our results show that these processes can cause large easily observed changes: 1) oxidation tends to introduce negative charge at the interface and 2) subsequent annealing tends to remove it. Further, 1) oxidation tends to decrease the effective doping in the n-Si and increase the effective doping in the p-Si adjacent to the sapphire while, 2) subsequent annealing has the opposite effect.