ETCHING REACTIONS OF C2H5I ON GAAS(100)

The surface reactions of ethyl iodide on GaAs(100) have been studied u sing Auger Electron Spectroscopy (AES), Low Energy Electron Diffractio n (LEED) and Thermal Desorption Spectroscopy in conjunction with isoto pe scrambling experiments with deuterium. Ethyl iodide was found to ad sorb dissociatively at room temperature, to form chemisorbed ethyl and iodine species. Recombinative desorption of molecular ethyl iodide co mpetes with the further surface reactions of ethyl and iodine. The eth yl species undergoes beta-hydride elimination reaction to form ethene, ethane and hydrogen, which all desorb into the gas phase. Iodine sele ctively etches surface gallium atoms as Gal, which subsequently desorb s at 520 K, and this species was the major halide etch product formed for all exposures of ethyl iodide. HI desorption forms a minor channel for the removal of surface iodine. As-2 desorption occurs from arseni c-enriched surfaces for temperatures greater than 600 K, and it is pos tulated that at high surface concentrations of chemisorbed arsenic dim ers, As-4 desorption must also become feasible. LEED and AES studies s how that repetitive exposure of the gallium-rich GaAs(100)-(4 x 1) sur face with ethyl iodide followed by annealing to 700 K gives rise to th e arsenic-rich c(4 x 4) structure, and this observation is consistent with the thermal desorption data. A reaction scheme is proposed to acc ount for the observed desorption products, and the etching behaviour o f ethyl iodide is discussed in the light of the reaction mechanism elu cidated. (C) 1998 Published by Elsevier Science B.V. All rights reserv ed.