IN-SITU MEASUREMENT OF THE THERMAL AND PHOTO-ASSISTED MOVPE OF ZNTE USING LASER REFLECTOMETRY

In situ laser reflectometry has been used to study the growth kinetics of ZnTe under pyrolytic and photo-assisted conditions from diisopropy ltellurium (DIPTe) and dimethylzinc.triethylamine (DMZn.TEN). The grow th rate of ZnTe was monitored as a function of VI:II ratio, temperatur e and laser power density. From the results a model for the growth inv olving the surface decomposition of DIPTe via a bimolecular reaction w ith methyl radicals homolytically released from the decomposition of D MZn.TEN is proposed. The activation energy under pyrolytic conditions in the low temperature regime for a 1:1 VI:II ratio was found to be 27 .6 kcal/mol and under photo-assisted conditions this activation energy was seen to be lowered to 21.9 kcal/mol. The growth kinetics are expl ained in terms of two competitive processes. The decomposition of DMZn on the surface will be enhanced with increasing substrate temperature ; however, the desorption rate of DIPTe will also be enhanced. The com petitive nature of these two processes is seen to be particularly pron ounced under laser illumination at high power densities, where a growt h rate of 13 a.u./s was observed at 360 degrees C, laser power density 67 mW/cm(2), whereas at 380 degrees C for a similar power density the growth rate was seen to be reduced to 10.5 a.u./s.