相較於傳統的氮化鋁鎵/氮化鎵異質結構，氮化鋁銦/氮化鎵異質結構具有較高的二維電子氣濃度，使通道片電阻更進一步地降低，有助於降低場效電晶體之導通電阻。但是，過去之文獻顯示，氮化鋁銦異質結構受到較強烈的合金散射與界面粗糙散射的影響，其電子遷移率普遍低於氮化鋁鎵異質結構。在此異質結構中，即使使用氮化鋁間隔層減緩合金散射，其電子遷移率仍然偏低。因此，界面粗糙散射效應的改善應是提升氮化鋁銦異質結構之電子遷移率的首要課題。 本研究之主題為探討有機金屬化學蒸氣沉積法(MOCVD)磊晶條件對異質接面平整度之影響，並據以改善電子遷移率。一般而言，氮化鎵磊晶常用之載氣為氫氣，此研究顯示，在成長通道界面處改以氮氣作為載氣時，可抑制氫氣易引起之熱蝕刻缺陷的產生，有效地降低氮化鋁/氮化鎵通道界面之粗糙度，氮化鋁的表面平坦度可以從0.88 nm降低至0.65 nm。所製備的氮化鋁銦/氮化鋁/氮化鎵異質結構，在二維電子氣濃度高達2.1×1013 cm-2的情況下，電子遷移率仍可高達1360 cm2/V-s，達成通道片電阻低至215 ohm/sq的狀況。藉由磁阻量測之Shubnikov-de Haas oscillations與所萃取之量子散射時間可知，界面粗糙散射仍是此結構最主要之載子散射機制；而且二維電子氣濃度越高，此界面粗糙散射的影響就越大。;Compared to conventional AlGaN/GaN heterostructures, AlInN/GaN heterostructures have higher two-dimensional electron gas (2DEG) concentrations, which result in lower on-resistance of high electron mobility transistors (HEMTs). However, previous reports show that there exist stronger alloy scattering and interface roughness scattering in AlInN heterostructures. These make electron mobility lower than that in AlGaN heterostructures. The use of an AlN spacer to reduce alloy scattering cannot raise the electron mobility to a level comparable to that observed on AlGaN heterostructures. In order to improve the electron mobility of AlInN heterostructures, reducing interface roughness scattering should be of primary interest as well as importance. This study aims to investigate the effects of growth conditions on the smoothness of the heterojunction during metal-organic chemical vapor deposition (MOCVD) so as to improve the electron mobility in AlInN/AlN/GaN heterostructures. H2 is a typical carrier gas used in the growth of GaN by MOCVD. In this study, N2 carrier gas is used during the growth of GaN/AlN heterojunction to suppress the thermal etching by H2, and effectively reduce the interface roughness. The surface roughness of AlN film desreases from 0.88 nm to 0.65 nm. An AlInN/AlN/GaN heterostrure with electron mobility of 1,360 cm2/V-s is achieved with a 2DEG concentration of 2.13×1013 cm-2, leading to a low sheet resistance of 215 ohm/sq. Quantum lifetimes extracted from Shubnikov-de Haas oscillations of the AlInN/AlN/GaN heterostrures growth with H2 and N2 carrier gas indicate that interface roughness scattering is still the dominant scattering mechanism and it is even more significant in the samples with higher 2DEG concentrations.
