Thin semiconductor alloy films: Fabrication and physical properties.

摘要

The main emphasis of this thesis is on fabrication and physical properties of thin semiconductor alloy films. We investigated the detailed processes which play a role in fabricating these materials, and systematically investigated the links between the fabrication processes and physical properties of the alloys of interest.; Wide-gap semiconductor ternary alloys based on combining group-II and group-VI elements were grown by molecular beam epitaxy (MBE) over a wide range of compositions. The indices of refraction of these II-VI ternary alloys were measured at wavelengths below their respective energy gaps. A set of empirical parameters were establish for each alloy family, which can then be used to calculate the index of refraction for an arbitrary alloy composition at arbitrary wavelength. We applied the single effective oscillator (SEO) model to the experimental data in order to examine the effect of the covalency (or ionicity) of these semiconductor alloys, and to establish a method for extrapolating physical properties for different zinc-blende II-VI compounds. Furthermore, to fit the data near the energy gap, an additional term was added to the SEO model, which accounts for the effect of the direct energy gap.; In addition to our investigation of II-VI-based alloys, we also fabricated ferromagnetic semiconductor III-Mn-V alloys using a low temperature MBE technique. A thorough investigation of the physical properties (such as growth, magnetic, and transport properties) of III-Mn-V alloys was carried out. Specifically, we have studied two issues involving these materials: low temperature annealing of GaMnAs under different strain conditions; and fabrication of hybrid magnetic structures comprised of GaMnAs and ZnMnSe, the latter system involving antiferromagnetic interactions between the Mn ions.; Furthermore, we fabricated semiconductor superlattices of ZnSe_1−x Te_x and GaAs_1−xSb_x in which the chemical composition x varies sinusoidally along the direction of growth, and we studied the physical properties of these novel structures. The sinusoidal nature of the compositional profiles of these materials was inferred from the presence of only a single superlattice Fourier component in the x-ray diffraction spectra. Superlattice formation is additionally supported by systematic photoluminescence data.; In the end, we have fabricated and studied various digital alloys of III-V/Mn, where Mn-containing monolayers are “inserted” periodically in the III-V host material. Most of these digital structures exhibited ferromagnetism at low temperature, as demonstrated by hysteresis loops in the magnetization, and a metallic p-type conductivity with a strong anomalous Hall effect. The GaSb/Mn digital system exhibited high temperature ferromagnetic behavior, as demonstrated by a strong anomalous Hall effect characterized by hysteresis loops up to 400 K.