| Summary: | 碩士 === 國立交通大學 === 電子工程系所 === 93 === In the thesis, we have performed a theoretical investigation of the electrical properties and current-voltage characteristics of p-type bulk GaN and AlGaN/GaN superlattices. The calculations are based on the nonlinear Poisson equation, drift diffusion current model, and thermionic emission current model, with piezoelectric field effect taken into account. We found that the current-voltage characteristics of p-type AlGaN/GaN superlattices are better than those of p-type bulk GaN because the holes in AlGaN/GaN superlattices transport mostly by thermionic emission mechanism, while the holes in bulk GaN transport mostly by drift diffusion mechanism.
For wurtzite structure, We found that the current-voltage characteristics of AlGaN/GaN superlattices with different direction of piezoelectric field (Ga-face、N-face) is different. We also found that there is a spike potential on the boundary of superlattices due to the asymmetry of piezoelectric field. The spike potential will obstruct the holes and may cause too much joule heat to damage the device which uses the superlattices structure. For this reason, we used the structure of a gradual change of Al composition to eliminate the asymmetry of piezoelectric field and the spike potential, in order to improve the electrical properties of the AlGaN/GaN superlattices.
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