COMPARATIVE-STUDIES OF THE THERMAL-DECOMPOSITION OF TRITERTIARYBUTYLGALLIUM AND TRI-ISOBUTYLGALLIUM ON GAAS(100)

The adsorption of tritertiarybutylgallium (TTBG) and tri-isobutylgallium (TIBG) on GaAs(100), and on In and Al doped GaAs(100) Surfaces, has been investigated using AES, HREELS and thermal desorption techniques. Both TTBG and TIBG adsorb with high sticking probability on the GaAs surface at 300 K to form adsorbed phases in which the alkyl groups retain their integrity, as indicated by HREELS. Heating of both adsorbed phases results in competing reactions, in which some of the adlayer dissociates to form most likely the mono-Ga alkyl adsorbed species, while the remainder of the adlayer desorbs. The adsorbed species thereby formed decompose in the temperature range 500-600 K, evolving hydrogen and isobutene as the major volatile reaction products. Comparison with the well-characterised triethylgallium/GaAs adsorption system is made. The presence of Al has little influence on the surface chemistry of t-butyl species formed on the surface by the adsorption of TTBG; in contrast Al concentrations in excess of one third of a monolayer efficiently promote the irreversible deposition of carbon from TIBG. Indium also perturbs the surface chemistry of TIBG, favouring Ga alkyl desorption over decomposition.