Improved properties of high-Al-composition AlGaN/GaN high electron mobility transistor structures with thin GaN cap layers

摘要

GaN cap layers with thicknesses between 0.6 and 2.4 nm were shown to effectively suppress the degradation of the structural and electrical properties of AlGaN/GaN high electron mobility transistor (HEMT) structures with x_(Al) ～ 0.5 grown by metal-organic chemical vapor deposition (MOCVD). The formation of platelets and trench networks on free AlGaN surfaces was successfully mitigated by GaN cap layers as thin as 0.6 nm. Simultaneously, a rise in sheet charge density and mobility of the two-dimensional electron gas (2DEG) was observed, the magnitude of which depended on the AlGaN thickness. GaN was also shown to be a superior capping material compared to in-situ grown Si_3N_4.