Improvement of breakdown characteristics in AlGaN/GaN/AlxGa1 xN HEMT based on a grading AlxGa1 xN buffer layer

Abstract

To improve the breakdown characteristics of an AlGaN/GaN based high electron mobility transistor (HEMT) for high voltage applications, AlGaN/GaN/AlxGa1 xN double hetero structure (DH-HEMTs) were designed and fabricated by replacing the semi-insulating GaN buffer with content graded AlxGa1 xN(x¼x1!x2, x1>x2), in turn linearly lowering the Al content x from x1¼90% to x2¼5% toward the front side GaN channel on a high temperature AlN buffer layer. The use of a highly resistive AlxGa1 xN epilayer suppresses the parasitic conduction in the GaN buffer, and the band edge discontinuity limits the channel electrons spillover, thereby reducing leakage current and drain current collapse. In comparison with the conventional HEMT that use a semi-insulating GaN buffer, the fabricated DH-HEMT device with the same size presents a remarkable enhancement of the breakdown voltage.