EVALUATION OF CRACKING EFFICIENCY OF AS AND P PRECURSORS

The cracking behaviour of PH3, TBP and DitBuPH, AsH3 and TBAs was stud ied by mass spectrometry in a production-type MOMBE growth chamber. Th e measurements were performed varying the cracking temperature of the injector cells and the total material flux. The pyrolysis of the hydri des PH3/AsH3 essentially leads to the production of hydrogen and the d imers P-2/As-2. The decomposition of these source materials reaches ab out 90% at beam pressures in the range of 10(-7) Torr. Under identical conditions TBP, TBAs and DitBuPH are cracked better than 97%. However , the pyrolysis of the alkyl-compounds is accompanied by the formation of isobutene and hydrides. Consequently the decomposition of this PH3 and AsH3 produced during cracking is limiting the growth relevant cra cking efficiency to the values obtained for the hydrides. The addition al occurrence of dihydrides at beam pressures in the range of 10(-5) T orr suggests an initial decomposition process of the source materials via a radical formation mechanism. With respect to the stability of th e compounds a self-dissociation of TBAs in the bubbler under the produ ction of isobutane C4H10 and AsH3 was detected.