Low-Frequency Noise In Aln/Algan/Gan Metal-Insulator-Semiconductor Devices: A Comparison With Schottky Devices

We have systematically investigated low-frequency noise (LFN) in AlN/AlGaN/GaN metal-insulator-semiconductor (MIS) devices, where the AlN gate insulator layer was sputtering-deposited on the AlGaN surface, in comparison with LFN in AlGaN/GaN Schottky devices. By measuring LFN in ungated two-terminal devices and heterojunction field-effect transistors (HFETs), we extracted LFN characteristics in the intrinsic gated region of the HFETs. Although there is a bias regime of the Schottky-HFETs in which LFN is dominated by the gate leakage current, LFN in the MIS-HFETs is always dominated by only the channel current. Analyzing the channel-current-dominated LFN, we obtained Hooge parameters a for the gated region as a function of the sheet electron concentration n(s) under the gate. In a regime of small n(s), both the MIS- and Schottky-HFETs exhibit alpha proportional to n(s)(-1). On the other hand, in a middle n(s) regime of the MIS-HFETs, alpha decreases rapidly like n(s)(-xi) with xi similar to 2-3, which is not observed for the Schottky-HFETs. In addition, we observe strong increase in alpha proportional to n(s)(3) in a large n(s) regime for both the MIS- and Schottky-HFETs. (C) 2014 AIP Publishing LLC.