Confinement and concentration of electrons in Si δ-doped AlxGa1 − xAs(x = 0 and 0.35) grown by metalorganic vapour phase epitaxy

Abstract

Electron profiling is used to investigate segregation and diffusion of Si in δ-doped GaAs grown by metalorganic vapour phase epitaxy (MOVPE) at 650–725°C. The absence of asymmetric electron profile indicates that the segregation does not occur in MOVPE grown Si δ-doped GaAs. Spreading of the Si dopants is therefore mainly determined by thermal diffusion. The Gaussian-function like distribution of the electrons in as-grown Si δ-doped GaAs allows to derive Si diffusion coefficients at different temperatures. The electron concentration of Si δ-doped GaAs and Al0.35Ga0.65As is studied by varying δ-doping time, SiH4 partial pressure, reactor pressure, gas flow velocity, AsH3/SiH4 mole ratio and temperature. The electron density of Si δ-doped GaAs and Al0.35Ga0.65As increases with prolonging δ-doping time over the experimental range. Using relatively short δ-doping times, the Si desorption process unlikely approaches its equilibrium with the Si adsorption process. A significant increase of the electron density of Si δ-doped GaAs with reducing the gas flow velocity changed by either varying reactor pressure or H2 carrier gas flow rate suggests that the mass-transport of the Si doping species through a boundary layer and the heterogeneous reactions of SiH4 on the non-growing surface both play a negligible role in Si δ-doping. Si δ-doping concentration is dominated by adsorption of the Si doping species generated through homogeneous gas phase reactions. At a given δ-doping time, an increased SiH4 partial pressure, reactor pressure, AsH3/SiH4 mole ratio, temperature and/or a reduced carrier gas flow rate lead to an increased Si δ-doping concentration.