Low-sheet-resistance high-electron-mobility transistor structures with strain-controlled high-Al-composition AlGaN barrier grown by MOVPE

Abstract

We demonstrated low-sheet-resistance AlGaN high electron mobility transistors (HEMTs) using a strain-controlled high-Al-composition AlGaN barrier grown by MOVPE. We systematically investigated the effects of the AlGaN-barrier’s growth conditions on the electrical characteristics. We found that growing an AlGaN barrier with nitrogen as a carrier gas increases dislocation density in the AlGaN barrier, resulting in reduction of strain in the AlGaN barrier and the top of the GaN channel. Reduction strain in the GaN channel can improve electron mobility. Moreover, dislocation and impurity scattering are prevented using an AlN spacer. Finally, we achieved low-sheet-resistance HEMT structures with a high Al composition of over 0.60. The lowest sheet resistance is 211 Ω/sq. with electron mobility of 1820 cm2 V−1 s−1 using an Al0.68Ga0.32N barrier.