Improvement of breakdown characteristics in AIGaN/GaN/Al_xGa_(1-x)N HEMT based on a grading Al_xGa_(1-x)N buffer layer

摘要

To improve the breakdown characteristics of an AlGaN/GaN based high electron mobility transistor (HEMT) for high voltage applications, AlGaN/GaN/Al_xGa_(1-x)N double hetero-structure (DH-HEMTs) were designed and fabricated by replacing the semi-insulating GaN buffer with content graded Al_xGa_(1-x)N(x=x_1 → x_2, x_1 > x_2), in turn linearly lowering the Al content x from x_1 = 90% to x_2 = 5% toward the front side GaN channel on a high temperature A1N buffer layer. The use of a highly resistive Al_xGa_(1-x)N 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.