透過氮化鋁緩衝層增進磊晶品質並用以製作電性表現較好的高電子遷移率電晶體

Abstract

氮化鎵/氮化鋁鎵異質結構因寬能隙特性，故具有大的崩潰電場；且其極化效應產生二維電子氣(2DEG)，而有較高的電子遷移率，可被應用在高功率和高頻操作的元件上，是目前有潛力取代矽的半導體材料之一。 本篇論文研究利用氮化鋁緩衝層以成長高磊晶品質的氮化鎵，並用來製作氮化鎵/氮化鋁鎵高電子遷移率電晶體。因此第一部分為藉由拉曼頻譜分析與XRD分析的方式，分別分析數據的峰值和半高寬可以得到其殘留應力和差排密度，進而證實氮化鋁緩衝層確實提升晶體品質。 而因差排密度會影響電子元件的遷移率和飽和電流，因此製作出來的氮化鎵/氮化鋁鎵高電子遷移率電晶體若為有緩衝層的基板，其電性特性相較於一般的結構都有所提升。因而接連到本研究的第二部分高電子遷移率電晶體電性的量測結果，得到電晶體的最大汲極飽和電流在VG等於6V時從 481 mA/mm提升至522 mA/mm，導通電阻從14.98下降到12.61 Ω-mm。

AlGaN/GaN heterojunction has large critical electric field due to its wide bandgap and at the same time, because of polarization induced 2DEG, its electron mobility is very high. Therefore, we would like to use this kinds of materials to fabricate high-power and high-frequency device. Recently, GaN is one of the most promising materials to take place of Si in semiconductor field. This research compare the epitaxy quality of substrate with AlN buffer layer with substrate without buffer layer and furthermore, use these two substrate to make AlGaN/GaN HEMT individually. At first, we show the result of Raman and XRD to analyze crystal quality and residual stress of two substrates. We use the location and FWHM of peaks to calculate dislocation densities and stress and verify that using AlN buffer layer makes epitaxial quality better. Because dislocation density decreases electrical mobility and drain current, we expected that using substrate with AlN buffer layer to fabricate HEMT can behave better electrical properties. Thus, the next part of this research is to measure the electrical properties. We find that saturation drain current increases from 481 mA/mm to 522 mA/mm and on resistance decreases from 14.98 Ω-mm to 12.61 Ω-mm when gate voltage equals to six volt.