Compensation in MBE-grown GaAs doped with silicon and beryllium

Silicon doping is the most common means of producing n-type GaAs grown by MBE. However, samples grown with an intended carrier concentration of the order of 3×10¹⁹ cm^-3 exhibit considerable self-compensation. Localized vibrational mode (LVM) absorption spectra indicate high concentrations of [Si-X] complexes, where X is believed to be the gallium vacancy, V_Ga. It can be concluded that in this material, [Si-X] acceptors are the dominant compensating acceptor. In order to investigate the role of Fermi energy on the production of [Si-X] centres, electrical measurements, such as electrochemical capacitance-voltage profiling, Hall-effect measurement, and LVM infrared absorption spectroscopy were employed to investigate MBE-grown GaAs containing both Si and Be at concentrations exceeding 10 ¹⁹ cm^-3 and where the closely compensated GaAs has been either residually p-type or n-type. The former samples exhibit LVM absorption bands due to Si_Ga donors, Be_Ga acceptors and [Si_Ga-Si_As] neutral pairs. Consistency of the electrical and LVM requires that [Si-Y] centres are neutral. We conclude that in this material [Si_Ga-Si_As ] centres must be produced by diffusion of Si atoms at ~600°C