Metalorganic chemical-vapour-deposition (MOCVD) of InGaAs, BGaAs, and BInGaAs: Quantum chemical calculations on the mechanisms

Using the density-functional method, reaction energies and barrier heights are calculated for reactions of precursor molecules at steps of the GaAs(0 0 1) surface modelled by molecular clusters. The reaction behaviour of XZ3 molecules (X=B, Ga, In, As; Z=H, CH3) is investigated at double-layer steps of Ga- and As-rich surfaces. The energetic data provide assertions to the rate-limiting step, the efficiency of the precursor molecules, and the formed structures. The precursor molecules or the formed precursor fragment dimers preferentially bind in dimers at steps. In general, the deposition with hydrides XH3 is faster than with methyl molecules X(CH3)3. B(CH3)3 is less suitable for the boron deposition in alloys. The boron deposition by borane is very probable at boron dimers, is reduced at arsenic dimers (isovalent deposition), and is not possible at gallium and indium dimers (antisite deposition). The first case leads to the formation of a boron phase, what can be suppressed by working under excess of arsenic and reduced exposure of boron.