Scattering of Pulsed Trimethylgallium Beam from Clean and Oxidized GaAs Surfaces

In order to study the mechanism of selective-area growth in metalorganic molecular beam epitaxy (MOMBE), we examined the difference in the scattering of a pulsed trimethylgallium (TMG) beam from a clean (epitaxially prepared) GaAs surface and an oxidized GaAs surface, which is effective as a mask for selective-area epitaxy. Although a long surface residence ( 896 µs at 546 K) was necessary to interpret the time-of-flight (TOF) spectrum of TMG scattered from a clean GaAs surface, the TOF spectra of TMG scattered from an oxidized surface were well reproduced only by a translationally drifting Maxwellian velocity distribution (without a surface residence). We consider that the difference in the surface residence time during scattering causes the decomposition selectivity of a metalorganic source on clean and oxidized surfaces, which is the essence of selective-area growth. We also observed that the energy exchange between the mask surface and incident TMG molecules during scattering is small when the mask is effective for selective-area growth.