Surface Reaction Kinetics of Molecular Beam Epitaxial Growth of Cadmium-Telluride

The molecular beam epitaxial (MBE) growth of (001) CdTe has been investigated. The two theoretical models for MBE growth (thermodynamic and kinetic), were able to predict most aspects of growth such as elemental condensation temperatures, impurity sources, Sb bulk dopant concentrations, and Sb dopant profile broadening. A study of the surface kinetics provided valuable insight into the physical mechanisms of growth. Reflection high-energy electron diffraction desorption studies were performed on epitaxial (001) CdTe surfaces. Both Cd and Te desorption from CdTe were observed to follow a simple first order rate law. Activation energies of 1.92 +/- 0.07 and 5.1 +/- 0.4 eV were found for Te and Cd, respectively, on the CdTe surface. The congruent evaporation temperature was determined to be 340^circC. Under normal growth conditions (a substrate temperature of 300 ^circC and growth rate of 1 um/h) a Te-stabilized surface of (001) CdTe was found. The implications of these findings on high-quality crystalline growth are discussed. Analysis of secondary ion mass spectroscopy data showed that Sb had relatively slow bulk diffusion rates at MBE growth temperatures in CdTe (125 +/- 1 A^2s^{ -1} at 300^circC). An activation energy of 3.7 +/- 0.2 eV was found for Sb desorption from (001) CdTe. Reflection high-energy electron diffraction intensity oscillations were observed for the growth of (001) CdTe and used to study interface smoothness. The effect that photoassisted molecular beam epitaxy has on the reaction of Sb doping of (001) CdTe was investigated. Photoassisted MBE was observed to enhance Te desorption by a factor of 10 (activation energy = 0.15 +/- 0.02 eV) by a process which was not strictly thermal. The Cd desorption was not affected to within the experimental uncertainty. By increasing the Te desorption rate photoassisted MBE presents more sites for SB incorporation on the Te sublattice and increases p-type doping of CdTe.