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Physical degradation and preparation for in-situ microscopy of AlGaN/GaN-based HEMTs
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Physical degradation and preparation for in-situ microscopy of AlGaN/GaN-based HEMTs

Andrew Charles Lang
Master of Science (M.S.), Drexel University
Jul 2012
DOI:
https://doi.org/10.17918/etd-4118
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Abstract

Wide gap semiconductors Microwave transistors Materials Science
The most promising class of materials poised to take over the future of microwave power transistors are wide band gap semiconductors among which GaN is most exciting. A high electron mobility transistor (HEMT) made of an AlGaN/GaN heterostructure can take advantage of a sheet charge layer known as a two-dimensional electron gas (2DEG) to achieve superior properties compared to other materials such as Si, SiC and GaAs. Unfortunately AlGaN/GaN HEMTs are plagued by unknown reliability and there is no clear mechanism which describes how these devices degrade. Degradation of AlGaN/GaN HEMTs is a result of multiple mechanisms, and from a materials perspective it is most advantageous to study the physical degradation and microstructural changes of these electronic devices. During high voltage and high frequency operation AlGaN/GaN HEMTs experience irreversible degradation in their electronic properties, and this degradation has been attributed to physical degradation of the device1-7. By performing high resolution transmission electron microscope (HRTEM) imaging and taking advantage of the phase information within a bright field TEM image by performing Geometric Phase Analysis, a higher resolution and greater quantitative understanding of the degradation of AlGaN/GaN HEMTs can be achieved. Establishing the ability to reproducibly perform HRTEM and quantitative analysis on AlGaN/GaN HEMTs of varying amount of bias is only the first step on the road toward to the ultimate goal of performing in-situ TEM on these devices. Much of the ground work for in-situ studies has been laid out and key issues for moving forward are discussed.

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