Mechanisms for the low temperature photo-dissociation of alkyl precursors for the epitaxial growth of CdxHg1-xTe (CMT) are discussed. The roles of vapour and surface nucleation are considered in the light of the free radical model which also can provide methods for controlling the vapour phase photochemistry. Higher quality CMT has been grown at 250 °C by using dimethyl mercury as a source of free methyl radicals. Problems encountered in reducing growth temperature for multilayer epitaxy are considered for CdTe and HgTe and conditions established for epitaxial growth at 200°C.The roles of alkyl concentration, substrate temperature, UV intensity and free radical concentration are explored. Results on the first reported growth of CdTe deposition using a cw UV laser source are compared with the arc lamp grown layers.