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

Electron profiling is used to investigate segregation and diffusion of Si in delta-doped GaAs grown by metalorganic vapour phase epitaxy (MOVPE) at 650-725 degrees C. The absence of asymmetric electron profile indicates that the segregation does not occur in MOVPE grown Si delta-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 delta-doped GaAs allows to derive Si diffusion coefficients at different temperatures. The electron concentration of Si delta-doped GaAs and Al0.35Ga0.65As is studied by varying delta-doping time, SiH4 partial pressure, reactor pressure, gas flow velocity, AsH3/SiH4 mole ratio and temperature. The electron density of Si delta-doped GaAs and Al0.35Ga0.65As increases with prolonging delta-doping time over the experimental range. Using relatively short delta-doping times, the Si desorption process unlikely approaches its equilibrium with the Si adsorption process. A significant increase of the electron density of Si delta-doped GaAs with reducing the gas flow velocity changed by either varying reactor pressure or H-2 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 delta-doping. Si delta-doping concentration is dominated by adsorption of the Si doping species generated through homogeneous gas phase reactions. At a given delta-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 delta-doping concentration.