Thermal equilibrium concentrations of the amphoteric dopant Si and the associated carrier concentrations in GaAs

Expressions of the thermal equilibrium concentrations of Si in GaAs have been obtained in terms of fundamental constants of the involved materials. Silicon is an amphoteric dopant in GaAs, with four species: a neutral and an ionized shallow donor species occupying Ga sublattice sites, and a neutral and an ionized shallow acceptor species occupying As sublattice sites. The concentration of an ionized Si species is expressed by the concentration of the appropriate neutral species and the GaAs crystal Fermi level or the carrier concentration and the band gap energy level positions. The thermal equilibrium concentrations of the two neutral species are expressed by the relevant Gibbs free energies of formation and the As4 vapor phase pressure in the ambient. Using these equations, the long observed relations between the carrier and Si concentrations in different experiments involving both n- and p-type Si doping produced GaAs are quantitatively explained. A difference of ∼1.55 eV in the effective formation enthalpy between the neutral Si atoms occupying the As and Ga sublattice sites has been identified. Moreover, at high temperatures, the GaAs intrinsic Fermi level energy Ei appears to be higher than the midgap energy Eg/2 by ∼20–80 meV.