SN DOPING OF GAAS AND ALGAAS GROWN BY METALORGANIC MOLECULAR-BEAM EPITAXY

We have investigated Sn doping of GaAs and AlGaAs grown by metal-organic molecular beam epitaxy (MOMBE) by growing layers in which the Sn flux, as generated by an elemental Sn source, is periodically raised or lowered by changing the source temperature. The maximum doping levels obtained were 8 x 10(18) cm-3 at 500-degrees-C and 1 x 10(19) cm-3 at 600-degrees-C. The activation energy for Sn incorporation was approximately 3.22 eV for both GaAs and Al0.25Ga0.75As. Comparison of SIMS and Hall data shows that most of the Sn is electrically active. The shape of the profiles and the variation of Sn with oven temperature suggest that the Sn incorporation mechanism is the same as for material grown by molecular beam epitaxy (MBE). The presence of Sn surface accumulation and the absence of a growth rate dependence on Sn concentration indicate that the incorporation behavior is quite different than that of metalorganic chemical vapor deposition (MOCVD), in spite of the similar Group III sources employed.