THERMODYNAMIC INVESTIGATIONS ON THE LIQUID-PHASE EPITAXY OF HG1-XCDXTE LAYERS

Liquidus temperatures (450 < T(l) < 480-degrees-C) and the corresponding mixed crystal compositions (0.2 less-than-or-equal-to x less-than-or-equal-to 0.4) of Hg1-xCdxTe have been determined experimentally in the Hg-Cd-Te phase diagram as a function of various melt compositions. The data have been determined ex situ from special experiments as well as in situ from liquid phase epitaxy (LPE) experiments. At the same time, expressions for liquidus temperatures and materials constants have been derived from common equations describing the LPE growth kinetics. The materials constants appearing in these equations have been determined from LPE growth runs. LPE experiments have been performed in the step-cooling mode. Good lateral and vertical homogeneity in the composition as well as reproducibility of thickness, composition and good surface morphology can only be achieved after optimizing the homogenization procedure. The only reliable method is mechanical stirring of the melt solution. A criterion is given, characterizing the extent of source melt homogenization. The analysis of the experimentally determined correlations between layer thicknesses, growth times and deposition temperatures confirms the ex situ determined liquidus temperatures. Linear extrapolation of the x values to the liquidus temperatures allows the determination of the equilibrium mixed crystal composition.