THE ROLES OF ALUMINUM AND HYDROGEN IN IMPURITY CONTAMINATION OF ALGAAS GROWN BY MOMBE

We have investigated the effect of Al in the form of triethylaluminum (TEAl), trimethylamine alane (TMAAl), or elemental Al, and hydrogen, bonded to Group III or Group V precursors, on the oxygen and carbon concentrations of AlGaAs grown by metalorganic molecular beam epitaxy (MOMBE). Al was found to increase both the oxygen and carbon incorporation rates relative to GaAs. The primary source of the oxygen has been determined to be alkoxide contamination of the alkyl Group III sources. Similarly, the carbon contamination is due to carbon released from the decomposition of the alkyl Ga sources. For films grown with TEGa, this enhancement of the carbon uptake can be suppressed through the use of TMAAl which releases atomic hydrogen at the growth surface. Hydrogen does not appear to remove carbon generated from methyl radicals, as AlGaAs grown from TMGa exhibits hole concentrations > 10(19) cm-3, regardless of Al source, which increase with increasing AsH(x)/As2 ratio. We have also determined that increasing the AsH(x)/As2 ratio does not improve the crystallinity of the AlGaAs layers as determined by ion channelling analysis.