Characteristics of germanium-tin photodetectors and terahertz microbolometers.

摘要

Infrared and terahertz detectors have applications in fields such as medicine, industry, and scientific research. Methods for generating and detecting infrared and terahertz radiation are constantly evolving. This study will explore two general areas of terahertz and infrared technologies. First, real-time see-through imaging devices and applications using terahertz and long wavelength radiation will be investigated. Second, the growth and photocurrent spectroscopy of group IV optoelectronic detectors based on germanium quantum dots and GexSn1-x alloys will be investigated.;Terahertz radiation, synonymous with the extreme long-wavelength infrared radiation, was so named because of the frequencies that photons in this region of the electromagnetic spectrum exhibit. Many non-aqueous and non-metallic materials are transparent in the terahertz regime. Due to a dearth of room temperature detectors and high powered sources at terahertz frequencies, attempts to image at this frequency have met with limited success. In this work, the broadband imaging capabilities of a vanadium oxide microbolometer camera were investigated in the far infrared for applications in real-time terahertz imaging and analysis. A blackbody radiator was employed as the broadband terahertz source to illuminate the microbolometer array with all components in a nitrogen purged enclosure. Data was taken using several different levels of radiant flux intensity, and the noise equivalent differential temperature (NEDT) and the noise equivalent power (NEP) were recorded over a range of blackbody intensities. Real-time reflection-mode terahertz imaging with the microbolometer camera using a powerful synchrotron terahertz illumination source was then studied. For the first time, the capture of video-rate terahertz movies of hidden moving objects was demonstrated.;Group IV materials that can be monolithically integrated with silicon substrates were investigated as optoelectronic device candidates. Tensile strain in Ge quantum dots was confirmed, and a narrowing of the energy bandgap compared to bulk Ge was observed. Photoconductors fabricated from Ge xSn1-x alloys grown by molecular beam epitaxy (MBE) were characterized using photocurrent spectroscopy. The optical absorption edge was observed to decrease in energy with increasing Sn content, and the sample with the highest atomic percentage Sn was found to exhibit some properties consistent with a direct bandgap in k-space. The bandgap of the GexSn1- x alloys exhibited a temperature dependence. Bandgaps for the GexSn1-x alloys were estimated over the temperature range 0 K≤T≤300 K.