Electrical properties and device characteristics of InAlN/AlGaN/AlN/GaN heterostructure field effect transistors

We fabricated In(x)Al(1-x)N/Al(0.38)Ga(0.62)N/AlN/GaN heterostructures with flat surfaces and high electron mobility. The density of the two-dimensional electron gas varies over a wide range and decreases from 2.3 x 10(13) to 9 x 10(12) cm(-2). The electron mobility is higher than that of conventional InAlN/AlN/GaN in the range of In content in InAlN from 0.13 to 0.31. The mobility increases from 1050 to 1960 cm(2)/V.s with increasing In content. A high transconductance of 230 mS/mm and a large drain current of 1.2 A/mm are obtained in spite of the long 1.5-mu m gate and high contact resistance of about 1 Omega.mm in field effect transistors made from both structures. For the new structure, the subthreshold swing is lowered 1.5 to 0.6 V/dec. and the dark current is reduced 10(-2) to 10(-3) A/mm. The smoother surface of the new structure improves these parameters. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim