Reflectance anisotropy spectroscopy studies of the growth of carbon-doped GaAs by chemical beam epitaxy

Reflectance anisotropy spectroscopy (RAS) was used to study the carbon doping of GaAs grown by chemical beam epitaxy. Intrinsic carbon doping using trimethylgallium (TMGa) and arsine at a substrate temperature of 480°C was compared with extrinsic carbon doping using CBr4, triethylgallium and arsine. Samples were grown under a range of V:III ratios and the resultant surface reconstructions were determined by RAS. For samples grown under a (2×4)-like reconstruction the RAS spectra taken immediately after growth showed a strong (2×4)-like character rather than a return to a c(4×4)-like reconstruction as is seen for undoped GaAs. This was seen for both intrinsic and extrinsic doping and is attributed to a shift in the As-dimer bond energy for highly doped GaAs:C. Features in the RAS spectra at 3.1eV which developed during the cooling of the samples and which were clearly related to the carbon doping level were attributed to the linear electro-optic effect caused by doping of the underlying layer and not to surface structural effects. The C-doping level obtained using TMGa is known to vary strongly with V:III ratio and this was confirmed by post-growth analysis. IR spectroscopy of heavily doped samples grown using TMGa showed the presence of an aligned carbon complex (H–(CAs)2), lying parallel to [110] which has previously been seen in GaAs grown by metal-organic molecular beam epitaxy (MOMBE).