Differential scanning calorimetry studies of compound semiconductors: Thin film composition and interfacial chemistry

In this dissertation, novel applications of differential scanning calorimetry (DSC) for the study of compound semiconductors are described. The first section concerns the new application of DSC for the analysis of compound semiconductors. The Cd-Te system was used as a model to define the limits and power of this analytical tool. A series of mixtures of CdTe with Cd or Te were analyzed using DSC to determine the quantitative efficacy of this approach. The changes in the composition of the electrosynthesized CdTe were monitored as a function of deposition potential. Also, changes in compositional profiles as a function of solution hydrodynamics and TeO;The second aspect of these studies concerns the thermal formation of CdTe from constituent elements. The kinetics and topochemical details of the condensed-phase Cd + Te = CdTe reaction system were studied by DSC in conjunction with scanning electron microscopy (SEM) and energy-dispersive analysis of X-ray (EDAX). The exo-thermic reaction heat-release profiles were analyzed by DSC as a function of scan rate. A new kinetics measurement protocol was developed that combines isothermal DSC operation with dynamic heat-cool "probe" cycles for the Cd content of the reaction mixture. Both fine powders and large particles of Te were used to determine the reaction rate. The kinetics data are consistant with the contracting sphere model. The use of SEM and EDAX permitted unambiguous verification of the proposed model for the reaction topochemistry.;Finally, patterns of chemical reactivity were established at metal/semiconductor interphases by DSC. The metal/CdTe was used as a model system for this purpose. A total of nine different metals in terms of their chemical reactivity towards CdTe were measured. Both virgin and oxidatively etched semiconductor surfaces were prepared and reacted with these metals. The ramification of these results in terms of the electronic properties of metal/CdTe contacts are discussed. From these studies, DSC is shown to be useful for probing alternations in the CdTe surface chemistry as a result of etch treatment.