Co-pyrolysjs of DIPSbH and TMIn

Abstract

The reaction mechanisms for the pyrolysis of diisopropylantimonyhydride (DIPSbH, (C3H7)2SbH) alone and for the co-pyrolysis of DIPSbH and trimethylindium (TMIn, (CH3)3In) in D2 and H2 ambients have been studied in an isothermal flow-tube, “ersatz” reactor using mass spectrometry to analyze the reaction products. The rate limiting step in the pyrolysis of DIPSbH alone is the reductive coupling reaction, producing C3H8. Additional products are C3H6 and C6H14produced by disproportionation and recombination reactions, respectively, of C3H7 radicals produced during the second stage of DIPSbH pyrolysis. The mixture of DIPSbH with TMIn produces a nonvolatile adduct on the quartz walls immediately after mixing in the reactor even at room temperature. No products were evolved at room temperature. However, for reactor temperatures between 100 and 200°C, an alkane elimination reaction occurs, producing CH4. The remaining solid product is postulated to be [(CH3)2InSb(C3H7)2]n (n = 2 or 3). For temperatures greater than 200°C, the DIPSbH begins to pyrolyze independently. This temperature for the onset of DIPSbH pyrolysis is considerably above the temperature (125°C) at which pyrolysis begins for DIPSbH alone. This suggests that during co-pyrolysis formation of the adduct retards pyrolysis of DIPSbH. Apparently, dissociation of the adduct is necessary before the DIPSbH can pyrolyze independently. Co-pyrolysis of DIPSbH and TMIn between 250 and 375°C produces (C3H7)Sb(CH3)2 and (CH3)3Sb. Neither is found for the pyrolysis of DIPSbH alone. Considerably larger amounts of C2H6 are also detected at low temperatures (≤ 300°C). The ethane may come from the [(CH3)2InSb(C3H7)2]n via an intramolecular alkane elimination reaction. The high carbon contamination levels reported for InSb samples grown by OMVPE using these precursors at 300 and 325°C are postulated to be caused by the formation of (C3H7)Sb(CH3)2 during the co-pyrolysis of DIPSbH and TMIn, but not during the pyrolysis of each precursor alone.