The growth and characterization of silicon-germanium devices for optoelectronic applications

Abstract

Devices fabricated for optoelectronic applications based on group IV semiconductors have become an important field of study, specifically in the terahertz (THz) region of the electromagnetic spectrum. Silicon Germanium (SiGe) optoelectronic devices are attractive because of possible compatibility with existing silicon based devices and fabrication techniques. Silicon based optoelectronic devices for use in the THz range also exhibit lower free-carrier and reststrahlen-band absorption than in typical III-V compound semiconductors. ☐ This thesis reports resonant state devices grown on varying substrates by Molecular Beam Epitaxy (MBE) and Chemical Vapor Deposition (CVD). The control of beam fluxes and growth conditions make MBE an attractive method for growing high quality SiGe epitaxial layers. Low Temperature Epitaxy (LTE) by CVD, using a process chamber held at ultra-high vacuum (UHV) conditions, is also an attractive method for growth of SiGe layers. LTE exhibits precise control over film thickness, composition, and concentration profiles while the whole concentration range (0% to 100%) of Ge in SiGe is accessible. The design and fabrication of these resonant state devices by MBE and CVD will be outlined. ☐ Two methods were utilized to characterize the samples grown. X-ray diffraction (XRD) measurement techniques are used extensively for the analysis of semiconductor crystal structures. XRD measurements can give an approximate knowledge of the composition, layer thicknesses, and crystal quality. The crystal growth structure and quality of the grown layers were characterized using XRD. XRD techniques for epitaxial layers grown on bonded silicon-on-insulator (SOI) substrates are demonstrated. As the second characterization method, electroluminescence spectra of the SiGe devices were measured using Fourier Transform Infrared Spectroscopy (FTIR). Preliminary electroluminescence measurements of the resonant state devices grown by CVD and MBE are described.