WET OXIDATION OF ALAS GROWN BY MOLECULAR-BEAM EPITAXY

A 1 μm thick n-type GaAs layer with Si doping density of 1×10 17/cm3 and a 1000 Å thick undoped AlAs layer was subsequently grown by molecular beam epitaxy on the n+ GaAs substrate. To perform selective oxidation of the AlAs layer, the wafer was oxidized in N2 bubbled H2O vapor ambient at 370°C, 400°C, and 430°C, each for 3 hours. It is found that the defect-free selective oxidation of AlAs is very critically dependent on oxidation temperature. Both GaAs and AlAs layers were oxidized at the oxidation temperature of 430°C, and some defects were found by scanning electron microscopy (SEM) on the surface oxidized at 370°C. Oxidation was, however, stopped at the AlAs/GaAs interface at the oxidation temperature of 400°C, and no defects were found on the surface. By the slow ramp rate (5 mV/sec) high frequency (100 kHz) C-V measurement, the fixed charge density was estimated to be about 1×1011/cm2 for the metal-oxide- semiconductor (MOS) capacitor fabricated from the oxidized sample at 400°C. © 1994 American Institute of Physics.