Browsing by Author "Hickey, Ryan"
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Item Fabrication of Germanium Tin Microstructures Through Inductively Coupled Plasma Dry Etching(IEEE Transactions on Nanotechnology, 2021-09-30) Lin, Guangyang; Cui, Peng; Wang, Tao; Hickey, Ryan; Zhang, Jie; Zhao, Haochen; Kolodzey, James; Zeng, YupingGermanium tin (GeSn) with a Sn content of >12% has a great potential for optoelectronic devices due to its direct bandgap property. In this work, the anisotropic etching of GeSn with Sn content of 12.5% and selective etching of Ge over GeSn were explored by inductively couple plasma (ICP) dry etching to obtain various microstructures. Through adding oxygen into chlorine and argon and adjusting the process pressure, the anisotropic etching of GeSn was optimized with an ideal sidewall angle of 89 o . The optimized process is compatible with both positive and negative resists. By altering the ICP power, Ge etching recipes with low and high etching rates were developed, which are favorable for fabricating GeSn nano- and micro-structures, respectively. An etching selectivity of >126 for Ge over GeSn with Sn content of >10% can be achieved. With the optimized dry etching recipes, suspended GeSn microribbons and microdisks were realized. Ultimately, the suspended GeSn microstructures were transferred onto 40-nm-thick ZrO 2 on p + -Si to form a GeSn-on-insulator (GeSnOI) substrate. For a fabricated 45-nm-thick Ge 0.875 Sn 0.125 OI back-gated transistor, the subthreshold swing (SS) of 240 mV/dec is reasonably low for a non-optimized device, suggesting that the explored dry etching methods are promising for device processing.Item The growth of strain engineered germanium tin alloys for mid-infrared detectors by molecular beam epitaxy(University of Delaware, 2017) Hickey, RyanInterest in near and mid-infrared optoelectronic devices for sensing, security, medical imaging, and telecommunications has led to an immense effort to create new materials capable of filling these needs. As the applications for these infrared devices have become more ubiquitous, so too does the desire for cheaper and more efficient materials to meet the demand. As the industry pushes more towards complete device integration, there is also a heavy push specifically towards developing materials compatible with standard CMOS processing. To that end, the alloying of Tin with Germanium and Silicon has been shown to fit these requirements. ☐ During the course of this research on germanium-tin semiconductors, novel methods were developed for growing and fabricating electrical and optical devices with unusually high tin compositions, using silicon-compatible technology. The characteristics and limitations of the devices were measured and analyzed to understand their fundamental properties and to determine how well their performance compared to expectations from current theory. With increasing tin content, the optical devices exhibited a useful direct energy bandgap, which is unique compared to other Group-IV materials, and with operation extended from the near-infrared into the important mid-infrared wavelength regime, even into the long-wave infrared region. The performance of electronic devices, however, was less encouraging, and exhibited low carrier mobilities and high reverse leakage currents. These electrical properties were found partly due to the intrinsic narrow bandgap energy of germanium-tin, but also to the presence of background impurities and dopants, which it may be possible to reduce by using high purity materials and procedures that are compatible with the required low temperature epitaxy.