Charge and Mobility Enhancements in In-Polar InAl(Ga)N/Al(Ga)N/GaN Heterojunctions Grown by Metal-Organic Chemical Vapor Deposition Using a Graded Growth Strategy

In this paper, we investigated the Ga incorporation effect in InAl(Ga)N/Al(Ga)N/GaN heterojunctions grown by a close coupled showerhead metal-organic chemical vapor reactor and proposed a grading growth strategy, where the indium composition was graded from Al(Ga)N to InAl(Ga) N, to mitigate the deleterious effect of Ga carry-over on the transport properties of two dimensional electron gas (2DEG). In contrast to non-graded samples grown by conventional growth strategy without grading, hall measurements revealed significant charge and mobility enhancements for the graded samples, with an electron mobility of 1300 cm(2) V-1 s(-1), a sheet charge density of 2.35 x 10(13) cm(-2) and a resultant low sheet resistance of 205 Omega/square compared to the non-graded sample with an low sheet charge density of 1.4 x 10(13) cm(-2) and mobility of 1100 +/- 50 cm(2) V-1 s(-1). The reason of the enhancements were then analyzed by transmission electron microscopy (TEM) and atom probe techniques, which revealed that grading strategy led to a higher average Al composition in the barrier layer. (C) 2012 The Japan Society of Applied Physics