Growth of carbon-doped GaAs, AlGaAs and InGaAs by chemical beam epitaxy and the application of in-situ monitoring

Heavily carbon-doped GaAs, AlGaAs and InGaAs were grown by chemical beam epitaxy using CBr4 as the extrinsic dopant source. SIMS-derived C concentrations of up to 10(21) cm(-3) were achieved for GaAs. Comparison of SIMS, Hall and CV data showed 100% activation for C levels as high as 5 x 10(20) cm(-3) in GaAs. Oscillations in the reflectance of the growing GaAs films were monitored at 670 nm in real time using the dynamic optical reflectivity (DOR) technique. These oscillations arise from small changes in the refractive index due to carbon doping and are readily observed at doping levels of 2 x 10(19) cm(-3) and above. A reduction in the growth rate of heavily C-doped GaAs was observed and this was attributed to etching by Br species associated with the use of CBr4. In-situ etching of previously grown GaAs/AlGaAs structures using CBr4 was also monitored optically, confirming that etching is independent of the supply of TEGa. The growth and doping of ternary compounds, particularly InGaAs, was complicated by the etching of the group III species. InGaAs layers that were carbon-doped were found to be significantly In deficient at doping levels above 10(19) cm(-3); this was attributed to a higher etch rate for In.