Design, fabrication, and characterization of microdisk terahertz sources based on silicon-germanium alloys

In the past few years, light emitters and detectors that operate in the so-called terahertz gap of the electromagnetic spectrum (0.1–30 THz) have attracted much interest for applications in a variety of disciplines. In particular, areas such as far-infrared ranging and imaging, remote gas sensing, spectroscopy, and wireless communication may benefit a great deal from reliable and low-cost THz-systems.; This dissertation reports on the design, fabrication, and characterization of novel silicon/silicon-germanium microdisk resonators as components of SiGe terahertz emitters and lasers. These structures are intended to be utilized as reliable long-wavelength emitters and detectors, and possibly laser sources. The intended emission and detection frequency is in the 1–30 THz range. Research on the micro-machining of resonators and waveguides from samples of silicon/silicon-germanium multi-quantum-wells capable of emitting long-wavelength radiation, and on the characterization of the THz sources at cryogenic temperatures was performed. The work comprises the development of a novel anisotropic reactive ion-etching process producing smooth and nearly straight sidewalls in silicon, required for guiding and coupling of THz radiation. In addition, a virtually ideal doping-dependent two-step wet etch was developed to achieve freestanding all-silicon structures. The propagation of light inside the resonators was simulated by several approximation methods, and important results, such as resonance frequencies, quality factors, cut-off frequencies, and extinction lengths that govern the design rules for choosing appropriate dimensions are presented. The optical behavior, emissivities, and other important parameters were characterized by state-of-the-art F&barbelow;ourier-t&barbelow;ransform i&barbelow;nfrar&barbelow;ed (FTIR) spectrometry. Preliminary measurements of our quantum-well structures on simple sample geometries are described. An analytical framework within which FTIR measurements are interpreted was redesigned and reconfigured to be compatible with THz devices that operate at low temperatures and both in pulsed and continuous-wave mode. Modern measurement techniques, such as electroluminescence, photoluminescence, and photocurrent, were proposed, realized in part, and applied to characterize novel group-IV THz emitters. Strong (31 μW) emission in the terahertz frequency range was observed for quantum-well samples processed into mesa resonators, although laser operation has not been achieved to date.