Effects of the Fe-doped GaN buffer in AlGaN/GaN HEMTs on SiC substrate

Abstract

AlGaN/GaN high electron mobility transistors (HEMTs) with a Fe-doped GaN buffer on a SiC substrate were presented for power switching applications. In order to investigate the effects of an Fe-doped GaN buffer on device characteristics, HEMT devices with an Fe-doped GaN buffer on SiC were fabricated alongside with the conventional devices utilizing an unintentionally doped (UID) u-GaN buffer on SiC, and compared their device characteristics. The charge-injection-type hysteresis voltage shift ΔV of 42mV is observed in the C-V loop measurement, after the insertion of the Fe-doped HEMT as gate metal layer. The voltage shift ΔV of the u-GaN HEMT was 0.03mV. It shows that the Fe doping increases the trap at GaN buffer. However the off-state breakdown behavior of Fe-GaN (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BV</sub> =195V) was better than u-GaN (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BV</sub> =148V). The RF performance of Fe-GaN, the current gain cutoff frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) of 5.4GHz and f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 15.4GHz, also higher than the ft=4.2GHz and an f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> =13.4GHz of the u-GaN HEMT. It's shown that Fe-GaN has potential for high power and high frequency transistors.