Influence of processing and annealing steps on electrical properties of InAlN/GaN high electron mobility transistor with Al2O3 gate insulation and passivation

We report on preparation and electrical characterization of InAlN/AlN/GaN metal–oxide–semiconductor high electron mobility transistors (MOS HEMTs) with Al2O3 gate insulation and surface passivation. About 12 nm thin high-κ dielectric film was deposited by MOCVD. Before and after the dielectric deposition, the samples were treated by different processing steps. We monitored and analyzed the steps by sequential device testing. It was found that both intentional (ex situ) and unintentional (in situ before Al2O3 growth) InAlN surface oxidation increases the channel sheet resistance and causes a current collapse. Post deposition annealing decreases the sheet resistance of the MOS HEMT devices and effectively suppresses the current collapse. Transistors dimensions were source-to-drain distance 8 μm and gate width 2 μm. A maximum transconductance of 110 mS/mm, a drain current of ∼0.6 A/mm (VGS = 1 V) and a gate leakage current reduction from 4 to 6 orders of magnitude compared to Schottky barrier (SB) HEMTs was achieved for MOS HEMT with 1 h annealing at 700 °C in forming gas ambient. Moreover, InAlN/GaN MOS HEMTs with deposited Al2O3 dielectric film were found highly thermally stable by resisting 5 h 700 °C annealing.

► Influence of processing on performance of Al2O3 insulated InAlN/GaN MOSHEMT. ► InAlN surface oxidation causes a current collapse. ► Al2O3 dielectric layers were deposited by MOCVD. ► Annealed Al2O3 decreases channel sheet resistance and suppresses current collapse. ► Al2O3 dielectric found thermally stable after 5 h 700 °C annealing.