CARBON DOPING AND ETCHING EFFECTS OF CBR4 DURING METALORGANIC CHEMICAL-VAPOR-DEPOSITION OF GAAS AND ALAS

We have investigated carbon (C) doping and the reduction in the growth rate for GaAs and AlAs using CBr4 by metalorganic chemical vapor depo sition (MOCVD). The C concentration is proportional to [CBr4], [AsH3]( -1) and exp(-E(a)/RT) (E(a)=-1.4 eV in GaAs and -1.3 eV in AlAs). Thes e activation energies (E(a)) are equal to the Gibbs free energy of CBr 4 (1.3 eV) around the growth temperature. This indicates that the C in corporation is determined by the equilibrium of the vapor CBr3, which is easily decomposed from CBr4 in the gas phase. The C concentration o f AlAs is about one order of magnitude higher than that of GaAs. The a ctivity of C as an acceptor is close to 100% in GaAs and 80% in AlAs, and slightly depends on the growth temperature (T-g) and the V/III rat io. The reduction in the growth rate (gamma) for GaAs is proportional to [CBr4], [AsH3](-0.5) and exp(-E(a)/RT) (E(a)=1.2 eV), while for AlA s it is proportional to [CBr4], [AsH3](-1.0) and exp(-E(a)/RT) (E(a)=- 1.5 eV). These findings suggest that there are different types of etch ing mechanisms: for GaAs, the etching may be limited by the As removal , which is followed by fast Ga removal by HBr from CBr4 decomposition. On the other hand, for AlAs, the etching may be performed by adsorbed CBrx (x=1-3) during the doping process. The hole concentration (p) of AlGaAs is equal to the average of those of GaAs and AlAs. However, ga mma for AlGaAs is not a simple average of those for GaAs and AlAs. Thi s suggests that there is some alloy effect in addition to the above tw o etching processes.