Magnetic Resonance of Defects in Heteroepitaxial Semiconductor Structures

Abstract

Abstract : Research in the reporting period was concentrated on the continuation of a pioneering study of the defects present in thin film GaAs grown by MBE at temperatures between 190 and 300 degree. These layers have attracted recently great interest as buffer layers for the suppression of sidegating between MESFET devices and as active layers for ultrafast photodetectors working in the sub-picosecond range. A comprehensive analysis by magnetic resonance, infrared absorption, Hall effect, x-ray diffraction and particle-induced X-ray emission showed that the transport in these very As-rich layers is dominated by a hitherto unknown kind of hopping conduction between localized arsenic antisite defects present in concentrations up to 10(20)cm(3) and partly compensated by up to 10(18)cm(3) acceptors. The total concentration of excess As reached values pf 6x10(20)cm(3), corresponding to AsGa = 1.03. This was found together with a lattice expansion of up to 0.15 percent. Thermal annealing to temperatures higher than 500 degree C resulted in disappearance of the lattice expansion, a reduction of the antisite defect concentration by at least two orders of magnitude, and the disappearance of hopping conduction. Optically detected magnetic resonance (ODMR) experiments using luminescence emission were successfully implemented, but the luminescence of low-temperature grown GaAs turned out to be too small for detection by ODMR.