Parametric studies of Zn incorporation during δ-doping of AlxGa13-xAs grown by metal organic vapour phase epitaxy

Zn δ-doped AlxGa1−x As has been grown by metal organic vapour phase epitaxy using dimethylzinc (DMZn) as a doping precursor. Under our growth conditions. Zn δ-doping concentration decreases with increasing Al mole fraction of AlxGa13-x.As though Zn bulk-doping concentration appears to be constant. It was found that the hole density of Zn δ-doped AlxGa1−xAs is independent of the gas flow velocity and δ-doping time. The Zn δ-doping concentration is mainly determined by the equilibrium between the Zn adsorption and desorption processes with respect to the non-growing surface. The effect of mass-transport of the Zn through a boundary layer is negligible. The hole density of Zn δ-doped GaAs and Al0.35Ga0.65As grown at 650 °C exhibits a linear proportion to DMZn partial pressure, but for Zn δ-GaAs grown at 550 °C, the hole density has reached its saturated value. We observed that Zn δ-doping concentration significantly decreases with increasing temperature over the range of 600 °C to 700 °C, following an Arrhenius type relationship, for both Zn δ-doped GaAs and Al0.35Ga0.65As. The apparent activation energy is 2.04 eV for Zn δ-doped GaAs and 1.64 eV for Zn δ-doped Al0.35Ga0.65As. A model has been proposed to quantitatively explain parametric dependencies of Zn δ-doping concentration. It is revealed that reduction of Zn δ-doping concentration with increasing the Al mole fraction is most likely due to much stronger Zn desorption from the non-growing surface of AlxGa1−xAs than GaAs.