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High Temperature Heterojunction Bipolar Transistors

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The program objective was to develop deposition conditions for wide bandgap nitride semiconductors consistent with the requirements for either bipolar junction transistors or field effect transistors that can function at high speed in environments having elevated temperatures. The fundamental material for these studies was gallium nitride. We proceeded to define crystal growth parameters for preparing epitaxial thin films of InGa1-xN alloys which feature smaller bandgaps than GaN. To grow the nitride alloys, we used a modified metalorganic chemical vapor deposition MOCVD reactor which provided activated nitrogen generated as an electron cyclotron resonance microwave plasma. Samples were successfully prepared with compositions throughout the alloy series, viz, with bandgaps ranging from 1.9 eV InN to 3.4 eV GaN. The films were transparent with specular surfaces, and X-ray diffraction studies showed the GaN was single crystalline with the c-axis perpendicular to the substrate. The nitride alloys varied in color from deep red to yellow. We believe that is the first report of preparing InGa1-xN alloys in a plasma assisted MOCVD reactor. Because we can vary the bandgap of InxGa1-xN as desired, we can control the potential barrier between the base and emitter in a heterojunction bipolar transistor, or the spacer and the channel in a high electron mobility field effect transistor. Bipolar junction transistor, High temperature, ECR Plasma, Nitride MOCVD.

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Final rept. 9 Jan 1993-28 Feb 1994

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Approved for public release; distribution is unlimited.

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