Methyl exchange reaction of trimethylindium on GaAs(100) and the preferential etching of gallium

Abstract

We have observed a heterogeneous methyl exchange reaction between trimethylindium (TMIn) and Ga atoms on GaAs(100) which could be important in controlling stoichiometry in III–V compound semiconductor films containing In and Ga, prepared from group-III-alkyl sources. Adsorbed layers were prepared by dosing clean GaAs (either Ga- or As-stabilized) with TMIn near room temperature, to saturated coverage (1.7 × 10 14 In atoms/cm 2). Total carbon and indium coverages were monitored by X-ray photoelectron spectroscopy (XPS). Samples were heated to ~ 500° C at a rate of 1.6° /s and desorption products were detected by a differentially pumped quadrupole mass spectrometer. TMIn decomposes to form a Ga-alkyl product (either Ga(CH 3) 2, Ga(CH 3) 3, or a mixture) which desorbs between 70 and 350 ° C, and CH 3 which is detected between 220 and 450 ° C. The Ga-alkyl yield was higher for Ga-stabilized surfaces, while the yield of CH 3 was greater for As-rich surfaces. On both Ga- and As-rich surfaces, the yields of Ga(CH 3) x and CH 3 are, within experimental error, the same as those measured for trimethylgallium decomposition. The preferential “etching” of Ga by TMIn is a likely explanation for the observed reduction in the Ga incorporation probability in InGaAs films prepared from metal-organic molecular beam epitaxy. It could also explain the In-rich surfaces left after CH 4/H 2 plasma etching of InGaAsP.