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Adam's Project Page - RISE Summer 2006 |
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Intern: Adam Schaller, Materials Science and Engineering,
Michigan Technological University
Mentor: Christy Poblenz
Faculty Supervisor: James Speck
Department: Materials |
CHARACTERIZATION OF BULK GaN AND AlGaN/GaN HETEROSTRUCTURES GROWN BY MOLECULAR BEAM EPITAXY
Peerless long-range communication via cell phone or other device requires a high frequency signal. To achieve these frequencies transistors must be manufactured to operate under high power, high temperature conditions. The demand for high performance transistors requires increasingly specialized materials. GaN and its alloys with AlN provide a large band-gap material for such applications. Typical band-gap values for semiconductors range from 0.360eV to 2.170eV whereas GaN has a band-gap of 3.4eV. To grow a GaN/AlGaN heterostructure with favorable electrical characteristics a developed understanding of how physical properties affect electrical properties is necessary. Dislocation density, surface morphology, growth conditions, and impurities play an important role in the device quality. To observe these qualities, in-situ and post growth characterization was employed. During growth, reflective high energy electron diffraction was used to qualitatively determine the thickness of the Ga and AlGa on the surface of the substrate. Post growth atomic force microscopy (AFM) revealed varying surface morphologies as the III/V ratio changed during growth. The hall test was utilized to compare the charge density and electron mobility of the heterostructures to their surface morphologies. A relationship between electrical properties and growth conditions was established with the combined hall and AFM data.
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