A study of the OMVPE growth mechanisms using internal reflectance spectroscopy to examine adsorption of TMGa and NH3 and surface reactions between them

Internal reflection spectroscopy spectra show that NH₃ and ND₃ chemisorb onto (100) and (111)A GaAs surfaces. Adsorption occurs by the formation of Ga—N bonds via Lewis acid-base reactions which are identified by an absorption band between 1325 and 1100 cm⁻¹ with peaks near 1285, 1220 and 1150 cm⁻¹. No NH₃ absorption bands are detected when the (111)B surface is exposed. TMGa also chemisorbs onto the (100) GaAs surface. The adsorption spectra of NH₃ + TMGa is a function of the order in which the reactants are introduced. When NH₃ is introduced first, the reactivity is much greater as is evidenced by the almost total elimination of absorption peaks associated with N—H and CH₃ peaks which suggests that the reactions are surface catalyzed methane elimination reactions. Implications of the requirement that the hydride be adsorbed and the methyls react with the hydrogen atoms from the hydride to ALE and MOMBE growth are discussed. Also, consistent explanations are presented for why growth on the (111)B surface is difficult, the growth rate is independent of the hydride partial pressure under normal growth conditions, the incorporation of C into GaAs has an orientational dependence, and As is more preferentially incorporated into GaAsP at the lower growth temperatures.