Date

2016

Document Type

Thesis

Degree

Master of Science

Department

Electrical Engineering

First Adviser

Tansu, Nelson

Abstract

As the demand for smaller and more efficient electronics continues to grow, the technological advances of silicon begins to plateau. For this reason, researchers have been increasingly interested in other semiconductor materials, such as III-V semiconductors. Gallium nitride has proved to be a particularly useful material and research has gone into development of GaN based transistors, specifically the high electron mobility transistor (HEMT). One of the difficulties of the GaN based HEMT is creating a normally off device, while also limiting gate leakage. This thesis explores design possibilities for a MOSHEMT structure in an attempt to shift the threshold voltage as positively as possible. Specifically, options for the top semiconductor layer are explored and it is shown through TCAD simulations that due to lower spontaneous polarization, AlGaN is optimal for a less negative/more positive threshold voltage. Following this, options for the gate oxide are explored, including the use of multiple oxides. It is shown again through TCAD simulations that due to an electric dipole at the interface between high-k oxides and SiO2, it is possible to create devices with thresholds shifted closer to a normally off device than with the use of a single gate oxide. All TCAD results are supported by a mathematical MOSHEMT model, and future directions for exploring the possibility of a normally off GaN based MOSHEMT are proposed.

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