OMVPE growth mechanism for GaP using tertiarybutylphosphine and trimethylgallium

Abstract

The pyrolysis mechanism of tertiarybutylphosphine (TBP) on a GaP surface and also of mixtures of TBP and trimethylgallium (TMGa) for the growth of GaP were investigated. The reaction products for the decomposition of TBP alone on a GaP surface are similar to the products on an SiO 2 surface, i.e. C 4H 10, C 4H 8, PH 3 and H 2; however, the products are more strongly dominate by the C 4H 10 species. The addition of TMGa to the gas mixture formed additional products CH 4,CH 3D and (CH 3) x PH 3− x ( x = 1–2). The increased decomposition of TMGa at high TBP/TMGa ratios indicates that TBP enhances TMGa decomposition, but the decomposition of TBP is hindered by the presence of TMGa. The decomposition of TBP on a GaP surface occurs via a chain reaction. Surface adsorbed PH x species ( x=1–2) react with adsorbed TBP to form the volatile reaction product C 4H 10, and also propagate the PH x radicals. The terminating step in this chain reaction is the recombination of the adsorbed PH x species to form P x H 2, and/or PH 3 molecules which then desorb. Additional chain terminating steps occur when TMGa is introduced. The PH x species react with adsorbed TMGa molecules to grow GaP, thus depleting the surface radical population, resulting in reduced TBP decomposition. The reactions between the surface adsorbed radicals resulting from TBP decomposition and the group III alkyls may be responsible for the low carbon incorporation observed in the organometallic vapor phase epitaxial (OMVPE) growth using TBP.