CRITERIA FOR THE DESIGN OF MONOALKYLPHOSPHINE PRECURSORS FOR INP METALORGANIC VAPOR-PHASE EPITAXY

We have studied the reaction between n-butylphosphine and sec-butylpho sphine with trimethylindium in the dihydrogen atmosphere of an InP met alorganic chemical vapour deposition (MOCVD) reactor using Fourier tra nsform infrared (FTIR) spectroscopy, since these precursors are struct urally related to tertiarybutyl phosphine, an established InP MOCVD pr ecursor. It is found that at room temperature under conditions designe d to amplify precursor interactions an undesirable pre-reaction occurs between sec-butylphosphine and TMIn resulting in a clear, viscous, in volatile liquid. For n-butylphosphine a similar reaction is observed b ut to a much lesser extent than that for the case of the sec-butylphos phine. We have further characterised the structure of the involatile p roduct formed in the case of sec-butylphosphine using FTIR spectroscop y and have assigned this structure to that of a polymer of the type (M e-In-P-sBu)(n). We have made a comparison of these findings with data previously reported from our laboratories for the precursors tertiaryb utylphosphine, cyclohexylphosphine, cyclopentylphosphine, benzylphosph ine and cyanoethylphosphine. With the exception of tertiarybutylphosph ine all of the precursors studied give rise to an undesirable pre-reac tion with TMIn resulting in an involatile product. This is believed to be a quite general phenomenon for this system with the polymer having the generic structure (Me-In-P-R)(n). The uniqueness of tertiarybutyl phosphine has been examined in the light of these data using a series of proposed reaction steps and simple molecular modelling and it is su ggested that the key to the lack of pre-reaction in the case of tertia rybutlyphosphine lies in a combination of its base strength and struct ure (steric effects) in relation to the other phosphines studied.