The growth and fabrication of terahertz emitting devices and lasers

Over the last few years, the advent of terahertz (THz) technology has initiated the exploration of novel approaches to applications in such areas as homeland security, biomedical non-ionizing imaging, secure short-range and satellite-to-satellite communications, chemical and environmental sensing, quality control, and ranging. The broad commercialization of these techniques, however, requires compact, reliable, and low cost terahertz active devices. Si-based THz devices are especially attractive due to possible integration with complementary MOS circuitry, and to lower free-carrier and reststrahlen-band absorption than in typical III-V compound semiconductors.; In this dissertation, we describe several approaches that can be utilized to fabricate electrically pumped Si-based CMOS compatible terahertz emitters. We have demonstrated terahertz-emitting devices utilizing intersubband transitions in strained silicon-germanium quantum cascades. We employed a novel approach involving transitions between confined states associated with light-holes and heavy-holes, which may lead to Si-based quantum well terahertz light emitters with higher output power than previously demonstrated. The design and fabrication of these devices is outlined.; Terahertz emission from devices using transitions between resonant acceptor states formed by the built-in strain in boron-doped epitaxial SiGe quantum wells was also achieved. Population inversion can be realized using this technique, and a THz laser source is feasible.; We have furthermore shown terahertz emission from dopant energy level transitions in electrically pumped Si devices containing shallow acceptors and donors. The results of theoretical modeling explaining the experimentally observed dependence of emitted power on the device temperature and pumping current are presented.; We will give a comparison of these techniques concerning emission frequency, fabrication complexity, operating temperature, expected power output, and potential for refinement.; We have also investigated the feasibility of electrically tunable THz emitter based on intersubband transitions in asymmetric SiGe quantum wells. Theoretical calculations of the confined state energies in stepped quantum wells are presented in combination with a design for a cascaded device.