PRODUCTS OF PULSED LASER-INDUCED THERMAL-DECOMPOSITION OF TRIETHYLGALLIUM AND TRIMETHYLGALLIUM ADSORBED ON GAAS(100)

Products of pulsed laser-induced decomposition of triethylgallium (TEGa) and trimethylgallium (TMGa) chemisorbed on GaAs(100) were determined and compared to those observed in thermal desorption. The desorbing products, C2H5, C2H4, and Ga(C2H5)x (x = 2 and/or 3) for TEGa decomposition, and CH3 and Ga(CH3)x (x = 2 and/or 3) for TMGa, are the same as those produced in thermal desorption. However, rapid substrate heating with the pulsed excimer laser causes large changes in the relative yields. With laser induced heating, Ga-alkyl desorption is almost completely suppressed in favor of further decomposition to yield hydrocarbon products and leave Ga on the surface, while in thermal desorption the Ga-alkyl is a major product. Furthermore, for laser-induced thermal decomposition of TEGa, C2H5 production is enhanced with respect to C2H4. These effects are ascribed to decomposition of chemisorbed GaR2(ads) (R = CH3, or C2H5), leading to formation of adsorbed GaR(ads) and desorption of R(g). This decomposition reaction is entropically favored over desorption of the Ga-alkyl, but has a higher activation energy. Consequently, decomposition is favored at the rapid heating rates, while desorption of GaR(x) dominates at slow heating rates. Competition between these desorption and decomposition reactions is likely important in the overall conversion of TEGa and TMGa to expitaxially grown, Ga-containing III-V compound semiconductor films. Arrhenius parameters are presented for the GaR2 decomposition reactions. These data should improve the accuracy of kinetic models for epitaxial film growth by chemical vapor deposition and molecular beam techniques.