| Cathodoluminescence (CL) technique was used to investigate various properties of semiconductor materials, including GaAs/Al{dollar}sb{lcub}0.3{rcub}{dollar}Ga{dollar}sb{lcub}0.7{rcub}{dollar}As quantum well structures, ZnSe-based laser structures and GaN films.; Diffusion lengths (L) of excited carriers in a GaAs/Al{dollar}sb{lcub}0.3{rcub}{dollar}Ga{dollar}sb{lcub}0.7{rcub}{dollar}As quantum well structure were measured at temperatures between 250K and 8K, using CL line scan measurements. The maximum value of diffusion length, L = 1.6 {dollar}mu{dollar}m, occurred at 100K. Smaller values were obtained at lower and higher temperatures, dropping to L = 0.85 {dollar}mu{dollar}m for 8K and to 0.34 {dollar}mu{dollar}m for 250K. Nonradiative surface recombination velocity (S) of {dollar}rm5.4times10sp3{dollar} m/sec for excited carriers at the sidewalls of etch-formed features based on a GaAs/AlGaAs quantum well structure was determined. CL intensity of etch-formed features was found to decrease with decreasing feature size. Using the independently measured L and S, the measured variation of luminescence efficiency with feature size can be predicted by a model for carrier diffusion.; Temperature-dependent behavior of nonradiative recombination processes associated with dark line defects (DLDs) in degraded ZnSe-based laser structures were investigated. The contrast between the DLDs and the adjacent material was found to decrease with decreasing temperature, which suggests that the nonradiative recombination processes associated with the DLDs require thermal activation. At temperatures below 200K, the temperature dependence indicated an activation energy of 6 meV. Above 200K, a greater activation energy of 16 meV was obtained. Spectral shifts of 0.5 nm{dollar}-{dollar}2 nm associated with the DLDs were observed in CL spectra, which imply that strain relaxation (responsible for red shifts) and/or concentration changes due to interdiffusion (responsible for blue shifts) may be involved.; GaN films grown on sapphire substrates by various techniques were characterized using CL spectroscopy and microscopy. The CL spectra was dominated by near band-edge emission. In some cases, deep-level emission was observed. The CL intensity of near band-edge emission increased linearly with excitation density (beam current), while that of deep-level increased sublinearly with beam current. A recombination model was used to interpret the excitation-density dependent behavior. Faceted island-like features of 2{dollar}-{dollar}3 {dollar}mu{dollar}m in diameter were observed on an MBE-grown, Mg-doped sample, which had much higher luminescence intensities and slightly shorter peak wavelengths than those of the background material. This is attributed to higher crystallinity and higher purity in the faceted islands. Degradation of near band-edge emission and growth of deep-level emission were observed under electron irradiation. |
