Investigation of Rh-based Schottky electrode on AlGaN/GaN heterostructure

Abstract

Electrical properties and thermal stability of Ni/Rh/Au gate AlGaN/GaN heterostructure field effect transistors (HFETs) have been investigated and compared to the conventionally used Ni/Au counterparts. The Ni/Rh/Au gate HFETs exhibit a lower gate leakage current and lower off-state drain current than the Ni/Au devices owing to the enhanced performance of Schottky contact. It has been found that, after thermal treatment at 500 °C for 500 mins, the maximum drain current (Imax) and peak transconductance (gm,max) of the Ni/Au gate HFETs drop by ∼17.2% and ∼7.2%, respectively. Further more, there is a shift of 14% in the threshold voltage (Vth). However, in the case of Ni/Rh/Au gate HFETs, smaller decrease of ∼7.2% and ∼4.5% in Imax and gm,max, respectively are seen. The shift in Vth is also smaller at 4.7%. Secondary ion mass spectroscopy (SIMS) measurements have revealed that the improved thermal stability of the latter is attributed to the insertion of the stable Rh between Ni and Au, which serves as a barrier layer, suppressing the inter-diffusion of the gate metals with the substrate. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.