以分子束磊晶研究極化感應形成p-型氮化鋁鎵

Abstract

我們以分子束磊晶，在氮化鎵基板上成長以極化感應產生的p-型氮化鋁鎵。藉由改變鋁含量梯度，氮化鋁鎵厚度，我們得到一系列的電洞濃度、電洞遷移率以及導電率之結果，透過XRD的量測，我們可獲得鋁的含量，在厚度為200奈米的樣品內，當鋁含量由75%降至34%，我們可以獲得9.4 x 10^17 cm-3的電洞濃度，27.9 cm^2/V-s 的電洞遷移率，以及0.23 Ω-cm的低電阻率。藉由降低氮化鋁鎵生長厚度去改變鋁含量梯度，可以發現隨著厚度降低，電洞濃度上升，電洞遷移率降低，導致電阻率上升，由reciprocal space mapping 量測可以得知生長在氮化鎵基板上的氮化鋁鎵，隨著鋁含量上升，應力釋放更明顯，在電洞濃度較高的樣品中，我們嘗試去摻雜鎂，雖然電洞濃度稍有增加，但由於電洞遷移率會下降，結果無法改善電阻率。

Polarization induced p-type AlGaN on GaN template with molecular beam epitaxy is grown. By decreasing Al content from 75 through 34 % along the c-axis in the Al-gradient AlGaN layer of 200 nm in thickness, hole concentration at 9.4 x 10^17 cm^-3, hole mobility at 27.9 cm^2/V-s, and resistivity at 0.23 Ω-cm are obtained. When we increase the Al-gradient rate by reducing AlGaN thickness, hole concentration can be increased, but hole mobility is reduced, leading to an increased resistivity level. A medium Al-gradient rate can lead to the lowest resistivity. From the measurement reciprocal space mapping, it is found that the strain in the AlGaN layer is partially relaxed unless the Al content is low. In a sample of a high hole concentration, Mg doping of a medium level does not significantly improve the resistivity because hole mobility is reduced with Mg doping.