The lattice locations of silicon impurities in GaAs: effects due to stoichiometry, the Fermi energy, the solubility limit and DX behaviour

An outline of infrared localized vibrational mode absorption spectroscopy relevant to silicon impurities in GaAs is presented. Absorption lines from Si_Ga donors, Si_As acceptors, Si_Ga-Si_As pairs, Si_Ga-V_Ga (Ga vacancy) pairs and a complex Si-X (involving Si_As and V_Ga) have been identified as well as lines from Si_Ga-Cu_Ga, Si_Ga-H, Si_As H and Si_Ga-B_As pairs. These observations are related to the electrical properties of n-type Bridgman, liquid-encapsulated Czochralski and molecular beam epitaxial (MBE) (001) GaAs, and to p-type liquid phase epitaxial and MBE (111)A layers. The discussion relates to dynamic site switching, effects due to counter-doping with shallow acceptors, the solubility of silicon, and DX behaviour observed in homogeneously doped material and proposed for delta -doped MBE (001) layers. The major problem is to understand the processes that limit the maximum carrier concentration that can be achieved in n-type crystals.