Influence of barrier thickness on AlInN/AlN/GaN heterostructures and device properties

Abstract

AbstractWe report on structural and device properties of AlInN/AlN/GaN transistor heterostructures grown by metal organic vapour phase epitaxy (MOVPE) on 2″ sapphire substrates with AlInN barriers of thicknesses between 4 nm and 10 nm. The In content and thickness of the thin AlInN barrier is shown to be well determinable by high‐resolution X‐ray diffraction (HRXRD). Room temperature Hall measurements yielded similar mobility between 1400 cm2V–1s–1 and 1520 cm2V–1s–1 on all samples and increasing sheet carrier concentration ns with rising barrier thickness resulting in a minimum sheet resistance value of 200 Ohm/□. The effect of surface passivation with Si3N4 on the electrical properties is investigated and found to strongly increase sheet carrier concentration ns of the two‐dimensional electron gas (2DEG) to values above 2×1013cm–2. Characterization of transistors with gate length Lg of 1.5 μm produced from the grown samples reveals high transconductance (gm) and a maximum drain current (ID) of 300 mS/mm and ∼1 A/mm, respectively. For the sample with 4.6 nm barrier thickness, a reduced gate leakage current (IGL) and a absolute value of the threshold voltage (Vth) of ‐1.2 V is detected. Radio frequency (RF) measurements of passivated samples lead to maximum current gain cut‐off frequencies ft of 11 GHz and maximum oscillating frequencies fmax of 25 GHz. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)