The influence of the 1st AlN and the 2nd GaN layers on properties of AlGaN/2nd AlN/2nd GaN/1st AlN/1st GaN structure

This is a theoretical study of the 1st AlN interlayer and the 2nd GaN layer on properties of the Al0.3Ga0.7N/2nd AlN/2nd GaN/1st AlN/1st GaN HEMT structure by self-consistently solving coupled Schrodinger and Poisson equations. Our calculation shows that by increasing the 1st AlN thickness from 1.0 nm to 3.0 nm, the 2DEG, which is originally confined totally in the 2nd channel, gradually decreases, begins to turn up and eventually concentrates in the 1st one. The total 2DEG (2DEG in both channels) sheet density increases nearly linearly with the increasing 1st AlN thickness. And the slope of the potential profile of the AlGaN changes with the 1st AlN thickness, causing the unusual dependence of the total 2DEG sheet density on the thickness of the AlGaN barrier. The variations of 2DEG distribution, the total 2DEG sheet density and the conduction band profiles as a function of the 2nd GaN thickness also have been discussed. Their physical mechanisms have been investigated on the basis of the surface state theory. And the confinement of 2DEG can be further enhanced by the double-AlN interlayer, compared with the InGaN back-barrier.