METHYL EXCHANGE-REACTION OF TRIMETHYLINDIUM ON GAAS(100) AND THE PREFERENTIAL ETCHING OF GALLIUM

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 × 1014 In atoms/cm2). 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(CH3)2, Ga(CH3)3, or a mixture) which desorbs between 70 and 350 ° C, and CH3 which is detected between 220 and 450 ° C. The Ga-alkyl yield was higher for Ga-stabilized surfaces, while the yield of CH3 was greater for As-rich surfaces. On both Ga- and As-rich surfaces, the yields of Ga(CH3)x and CH3 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 CH4/H2 plasma etching of InGaAsP. © 1990.