Fabrication and characterization of group IV alloy semiconductor devices

Date
2015
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University of Delaware
Abstract
The germanium-tin (GeSn) alloys comprise a non-equilibrium solid solution of two group IV elements. Their compatibility with integrated circuit processing makes them very useful for monolithic integration on silicon wafers. They have the important optical characteristic of an energy bandgap transition from indirect to direct in k-space with sufficient Sn content (above about 7 atomic % Sn). The Sn incorporation into Ge is limited, however, due to thermodynamic instability and also the difficulties of material growth. Nevertheless, non-equilibrium growth techniques have been used to prepare high quality GeSn alloys, which can be fabricated into optoelectronic devices. In this work, GeSn is grown up to 12% Sn by Molecular Beam Epitaxy, fabricated into devices using Clean Room processing, and characterized optically and electrically. This dissertation presents work on the electrical and optical characterization of GeSn/Ge heterojunction devices. P-N heterojunction diodes were fabricated from layers of boron doped p-type GeSn grown by MBE on n-type Ge-substrates. GeSn pn diodes with varying Sn content were studied to extract diode electrical parameters. The Photoresponse of GeSn/n-Ge heterojunction devices was investigated with different Sn contents. Electrical and optical devices sometimes use high profile structures including microdisks and resonators that are fabricated by methods such as deep etching. A simple fabrication method to achieve the deep undercutting required by microdisks by employing dry-processing reactive-ion etching (RIE) is investigated. The effects of key RIE parameters such as chamber pressure, and radio frequency (RF) power on the etch rates are reported for a cyclic method that can achieve very deep structures. This cyclic RIE technique can be used for many materials such as Si, Ge, and GaAs, which would use a variety of different gas chemistries The last section of this dissertation describes the fabrication and characterization of magnetic tunnel junction (MTJ) for microwave applications, which have been extensively investigated. In this work, a MTJ was designed, fabricated and tested for use as microwave phase detectors so that they can be used for microwave imaging, etc.
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