P型氮化鋁鎵/氮化鎵超晶格之電性模擬

Abstract

本論文利用漂移擴散電流模型及熱離子發射電流模型且考慮壓電場效應下，計算P型塊材氮化鎵及氮化鋁鎵/氮化鎵超晶格之電流電壓特性，發現P型氮化鋁鎵/氮化鎵超晶格之電洞藉由熱離子發射機制產生之電流電壓特性可以比塊材氮化鎵之電洞藉由漂移擴散機制產生之電流電壓特性還好。 對於氮化鎵的wurtzite結構，我們也研究不同方向(Ga-face、N-face)之壓電場對於氮化鋁鎵/氮化鎵超晶格之電流電壓特性之影響，進而發現壓電場之不對稱效應會造成超晶格之邊界出現尖型能障，阻礙電洞流動而造成跨壓，損害元件的操作特性，因而提出了在氮化鋁鎵中採用漸變式鋁之組成成份來消除壓電場之不對稱效應，改善超晶格邊界之尖型能障，進而改良元件操作特性。

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.