Effects of the Capping and the Wetting Layers on the Electronic Properties of Self-assembled Pyramidal CdTe/ZnTe Quantum Dots

Effects of the Capping and the Wetting Layers on the Electronic Properties of Self-assembled Pyramidal CdTe/ZnTe Quantum Dots

The electronic properties of self-assembled pyramidal CdTe/ZnTe quantum dots (QDs) are inves- tigated as functions of the capping and the wetting layer thicknesses. The three-dimensional strain fields induced around the QD in the material matrix are analyzed based on the linear elasticity theory of solids for varying thicknesses of the capping and the wetting layers. The normal strains in the direction of the QD apex is shown to be continuous across the wetting layers for the CdTe/ZnTe QD system, in contrast with those of the InAs/GaAs QDs, which show discontinuities across the wetting layer due to the differences in the material parameters such as Poisson"s ratio and Young"s modulus of CdTe/ZnTe QD at the interface between the wetting layer and the substrate. The effect of the strain fields on the conduction and the valence subband energies are numerically investigated based on the eight-band kㆍp Hamiltonian. For a fixed capping layer thickness, the transition energy between the ground states in the conduction and in the valance subbands are found to decrease with increasing wetting layer thickness. On other hand, the transition energy shifts upward as the capping layer thickness increases, regardless of the thickness of the wetting layer. We ¯nd the transition energy difference between two capping layer thicknesses above 250 ºA is on the order of 10 meV. We conclude that proper size controll of the capping and the wetting layers for CdTe/ZnTe QDs is required to understand the electronic and optical properties of the QDs.

The electronic properties of self-assembled pyramidal CdTe/ZnTe quantum dots (QDs) are inves- tigated as functions of the capping and the wetting layer thicknesses. The three-dimensional strain fields induced around the QD in the material matrix are analyzed based on the linear elasticity theory of solids for varying thicknesses of the capping and the wetting layers. The normal strains in the direction of the QD apex is shown to be continuous across the wetting layers for the CdTe/ZnTe QD system, in contrast with those of the InAs/GaAs QDs, which show discontinuities across the wetting layer due to the differences in the material parameters such as Poisson"s ratio and Young"s modulus of CdTe/ZnTe QD at the interface between the wetting layer and the substrate. The effect of the strain fields on the conduction and the valence subband energies are numerically investigated based on the eight-band kㆍp Hamiltonian. For a fixed capping layer thickness, the transition energy between the ground states in the conduction and in the valance subbands are found to decrease with increasing wetting layer thickness. On other hand, the transition energy shifts upward as the capping layer thickness increases, regardless of the thickness of the wetting layer. We ¯nd the transition energy difference between two capping layer thicknesses above 250 ºA is on the order of 10 meV. We conclude that proper size controll of the capping and the wetting layers for CdTe/ZnTe QDs is required to understand the electronic and optical properties of the QDs.