Study of the gas phase chemistry in the silicon doping of GaAs grown by metalorganic vapor phase epitaxy using tertiarybutylarsine as the group V source

Gas phase decomposition studies have been combined with metalorganic vapor phase epitaxy (MOVPE) growth and doping experiments to investigate the mechanism behind the Si doping of GaAs grown using tertiarybutylarsine (t-C₄H₉AsH₂ or TBAs) as the Group V source. The use of TBAs leads to an increase in the Si doping efficiency from both SiH₄ and Si₂H₆ sources and this enhancement was proposed to originate from the homogeneous generation of Si-bearing intermediates, (t-C₄H₉)SiH₃ (TBSi) and SiH₃AsH₂, from reactions between SiH₄ and the pyrolysis products of TBAs. We have investigated the formation and role of these intermediates in this Si doping chemistry. Results of our decomposition study show that TBSi pyrolyzes in the gas phase at relatively low temperatures to form SiH₄. Consequently, the use of TBSias a Si dopant source results in a Si doping efficiency and temperature dependence that is identical to SiH₄. TBSi is therefore not a likely route to increased Si incorporation. Our studies of the co-decomposition of TBAs and SiH₄ or Si₂H₆ show that SiH₃AsH₂ is a co-pyrolysis product of TBAs and Si₂H₆, but not of TBAs and SiH₄. Furthermore, there is no indication of gas phase interaction between TBAs and SiH₄. The results of this study suggest that homogeneous reactions are not as important in this doping chemistry as had previously been considered and that surface processes may instead be responsible for the increase in Si doping observed with TBAs.