The growth and characterization of Group IV alloys for near to mid-infrared detectors
Date
2016
Authors
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Publisher
University of Delaware
Abstract
Near infrared and mid infrared optoelectronic devices have become increasingly important for the telecommunications, security, and medical imaging industries. An infrared system fully integrated in a silicon chip manufactured in a high-volume CMOS foundry is therefore a much desired technology. Such a technology would allow the integration of mid-IR technology with new functionality, lower costs, smaller size, weight and power, and higher reliability. The focus of this dissertation is on the advancement of low temperature Group IV epitaxy of tin containing alloys for use in near to mid- infrared technologies. To that end, various epitaxial techniques and improvements were made and several detector device structures were characterized. ☐ Low temperature epitaxy is vital to achieve Sn containing Group IV films, and both ultra-high vacuum chemical vapor deposition (UHV-CVD) and molecular beam epitaxy (MBE) were utilized to this end. New precursors are needed in CVD to maintain film growth at reduced temperatures. The novel precursors tetrasilane and digermane were studied for their low temperature compatibility. Crystalline silicon and silicon germanium alloys were deposited and characterized, finding high quality, bulk-like films. Tin-chloride was investigated as a possible Sn precursor, but was found to etch Ge. Multiple innovations in GeSn epitaxy in MBE were made, including both n- and p-type doping and higher Sn concentrations than those previously achieved for devices. ☐ While careful consideration needed to be taken into account for the growth of GeSn, normal clean room processing was not found to have any adverse effect on the material. Photoconductive and photodiode type detectors of GeSn films on Si substrates were fabricated. The wavelength response of the material was measured to continually increase into the mid-infrared as the Sn content was increased, reaching almost 4µm for a 15.6% Sn device at room temperature. The responsivity of the detectors was measured, and characterized as a function of temperature. The bandgap was extracted as a function of alloy concentration and strain, and was found to closely follow what was predicted in literature. The work presented here advances the state of the art for high Sn content films, moving towards successful commercial integration and manufacturability.