GaN‐Based Vertical n‐Channel MISFETs on Free Standing Ammonothermal GaN Substrates

• Published in: Physica status solidi. A, Applications and materials science Vol. 215; no. 8
• Main Authors: Treidel, Eldad Bahat, Hilt, Oliver, Stöver, Julian, Hoffmann, Veit, Brunner, Frank, Ickert, Karina, Hochheim, Stefan, Naumann, Franziska, Gargouri, Hassan, Martinez, Bryan, Weyers, Markus, Würfl, Joachim
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 21.04.2018
• Subjects: Aluminum oxide; Ammonia; Annealing; Atomic layer epitaxy; Lifts; MISFET; normally‐off; PEALD Al2O3; Substrates; Threshold voltage; vertical GaN transistors
• ISSN: 1862-6300; 1862-6319
• DOI: 10.1002/pssa.201700422

In this work, a vertical n‐channel MISFET homoepitaxially grown on ammonothermal n‐type GaN substrates by MOVPE is demonstrated. The MIS gate module consists of plasma enhanced atomic layer deposition of Al2O3 combined with in‐situ NH3 plasma surface pre‐treatment. An annealing step performed at 350 °C in N2 ambient drastically improves device performance. It reduces the ON‐state resistance from ≈12.0 k Ω mm to ≈150 Ω mm, increases the ON‐OFF ratio from 106 to 108, and lifts up Ids_max from  ≈ 0.25 to ≈ 40 mA mm−1. The threshold voltage is above +5 V and the median vertical off‐state blocking voltage strength is ≈68 V μm−1. Accumulated C–V characterization of planar MIS‐capacitors on n‐GaN gives insight to mechanisms boosting device performance after annealing. A vertical n‐channel MISFET homoepitaxially grown on ammonothermal GaN substrates is demonstrated. An annealing step reduces the ON state resistance from ≈12.0 to ≈150 Ω mm, increases the ON‐OFF ratio from 106 to 108, and lifts up Ids_max from ≈ 0.25 to ≈ 40 mA mm−1. The threshold voltage is above +5 V and the median vertical off‐state blocking voltage strength is ≈68 V μm−1.