Near-field scanning optical microscopic investigations of immiscibility effects and photoreflectance contrast in III-V semiconductor materials

This thesis presents a near-field optical microscopy, NSOM, investigation of the microscopic immiscibility effects present in indium gallium phosphide alloys, which were grown by liquid phase epitaxy, LPE. The immiscibility within the alloy system results in composition fluctuations, which are observed as spatially varying shifts in the local band edge photoluminescence peak energy of the material. The NSOM-determined composition fluctuations were corroborated by electron spectroscopy for chemical analysis (ESCA) and x-ray diffraction studies. The magnitude of the composition fluctuations increased with the amount of lattice mismatch between the In1-xGaxP film and its GaAs substrate. These spatially varying composition fluctuations were correlated with the spatial variations in the topography of the material, as seen by NSOM. The composition fluctuations in this semiconductor are directly related to a thermodynamic miscibility gap in the phase diagram for the pseudobinary alloy (InP) _1−x(GaP)_x. Similar results to those found in this investigation may be found in other semiconductor alloys, since miscibility gaps exist in many other semiconductor alloy systems.; This thesis work has also resulted in the development of near-field scanning photoreflectance microscopy, NSPM, system for investigation of the microscopic contrast that results from spatial variations in the surface electric field. Quantitative measurements of the surface electric field have shown that a large photovoltage effect is present in NSPM and NSOM measurements. The magnitude of this photovoltage can be greater than the intrinsic local spatial variation in surface electric field, and it can therefore limit spatial resolution. The highest spatial resolution yet reported for the imaging of spatial variations in photoreflectance spectroscopic signals has been demonstrated with this system.