Investigations of AlGaN/GaN HFETs utilizing post-metallization etching by nitric acid treatment

This work investigates AlGaN/GaN heterostructure field-effect transistors (HFETs) processed by using a simple post-metallization etching (PME) treatment. Decreased gate length (LG) can be achieved by using nitric acid (HNO3) PME treatment owing to the high etching selectivity of HNO3 of Ni against the Au and GaN layer. Influences on LG, etched gate profiles and device characteristics with respect to different PME processing parameters by HNO3 treatment are systematically investigated. Optimum device performance is obtained as LG was reduced to 0.5 μ mb y using a1 μm long gate mask by immersing the device into a 45% diluted HNO3 solution for 35 s. Improved device performances, including maximum drain‐source current density (IDS, max: 657.6 mA mm −1 → 898.5 mA mm −1 ), drain‐source saturation current density at zero gate bias (IDSS0: 448.3 mA mm −1 → 653.4 mA mm −1 ), maximum extrinsic transconductance (gm, max: 158.3 mS mm −1 → 219.2 mS mm −1 ), unity-gain cut-off frequency (fT: 12.35 GHz → 22.05 GHz), maximum oscillation frequency (f max: 17.55 GHz → 29.4 GHz) and power-added efficiency (P.A.E.: 26.3% → 34.5%) compared to the untreated reference device, have been successfully achieved. (Some figures may appear in colour only in the online journal)