A mechanism for induced surface degradation of high-resistive GaAs during device fabrication

Abstract

Undoped, liquid-encapsulated-Czochralski (LEC)-grown, semi-insulating (SI) GaAs crystals were electrically characterized by temperature-dependent Hall effects and conductivity measurements to establish the mechanism for thermally induced surface degradation. X-ray photoelectron spectroscopy (XPS) was used to obtain depth profiles of the Ga and As composition, and the nature of the defect complexes and their changes were determined using Fourier-transform infrared spectroscopy (FTIR). Boron-related inhomogeneities were found to occur, and although it is normally considered a passive impurity, we conclude that it was in fact responsible for the detrimental p-conversion through the formation of BGa–Ga(i), BGa–GaAs, and BGa–VAs defect complexes. We propose that boron homogenization inhibits the escape of Ga from the crystal surface during annealing, leaving an excess of Ga in the p-converted layers. With FTIR we observed changes in the local vibrational-mode absorption of the acceptor defects SiAs, CAs, and the donors BGa, SiGa, and BGa–SiAs upon annealing. We present a theoretical analysis, which explains the observed changes in electrical characteristics on the basis of variations in deep-donor compensators, less deep donors, and net shallow acceptors, and conclude that higher device yields are achievable in SI GaAs if boron contamination can be reduced.