ELECTRIC-FIELD-ENHANCED EMISSION FROM A DISCRETE ENERGY-LEVEL AT THE GAAS OXIDE INTERFACE

The previously observed dominant discrete energy level in GaAs-oxide MOS diodes prepared by plasma oxidation of heavily doped GaAs (N(D) almost-equal-to 10(18) cm-3) exhibits strong distortions of the corresponding DLTS transients despite of the small-signal excitation. The main attribute of the distorted emission and capture characteristics is the well expressed variation of the experimentally estimated apparent activation energy of the DLTS peak (0.25 to 0.72 eV) for a set of different samples and bias conditions. This behaviour is treated quantitatively as a consequence of two basic processes: a) High-field phonon-assisted tunnel ionization and b) Poole-Frenkel lowering of the barrier. Microscopic parameters of the defect are deduced on the basis of the model calculations. Density of the defects seems to follow concentration of shallow impurities, suggesting that one deals with a complex defect, rather than a point defect.