PHOTODISSOCIATION DYNAMICS OF DMZN AT 193 NM - IMPLICATIONS FOR THE GROWTH OF ZNSE FILMS BY LASER-ASSISTED METALORGANIC CHEMICAL-VAPOR-DEPOSITION

The chemical dynamics of the photodissociation of dimethylzinc (DMZn) have been investigated using VUV absorption spectroscopy. An ArF excimer laser (193 nm) was used to photodissociate DMZn in a hydrogen atmosphere. A broadband pulsed VUV plasma light source was used to obtain absorption profiles of the resulting photoproducts as a function of time after the dissociation pulse. The time-resolved absorption profiles indicate that ground state Zn atoms remain unreacted for at least several milliseconds, while the only other species detected in absorption, methyl radicals, disappear within a few hundred microseconds. There was no indication of monomethylzinc (MMZn) or zinc hydride (ZnH) formation. The methyl radical decay followed a second-order reaction rate, indicating that the main by-product is ethane. This conclusion is supported by mass spectrometer data. Fluorescence from CH* radicals was also detected after the ArF laser pulse. Due to the high reactivity of CH radicals, it is likely that they combine with hydrogen to form methyl radicals within several microseconds. A model for the methyl radical diffusion to the growth surface is discussed. The possible carbon containing intermediates (MMZn, CH3, CH) are unlikely to reach the growth surface in significant concentrations. Thus, carbon incorporation should be minimal using laser-assisted metalorganic chemical vapor deposition growth technique.