Rectifying behavior in the GaN/graded-AlxGa1−xN/GaN double heterojunction structure

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Rectifying characteristics induced by the polarization fields are achieved in the GaN/graded-AlxGa1−xN/GaN double heterojunction structure (DHS). By grading AlxGa1−xN from x = 0.4(0.3) to 0.1, the DHS displays a better conductivity for smaller reverse bias than for forward bias voltages (reverse rectifying behavior) which is opposite to p–n junction rectifying characteristics. The mechanism of reverse rectifying behavior is illustrated via calculating the energy band structures of the samples. The band gap narrowing caused by decreasing Al composition could compensate the for the band tilt due to the polarization effect in AlxGa1−xN barriers, thus lowering the barrier height for electron transport from top to bottom. The reverse rectifying behavior could be enhanced by increasing the Al content and the thickness of the multi-layer graded AlxGa1−xN barriers. This work gives a better understanding of the mechanism of carrier transport in a DHS and makes it possible to realize novel GaN-based heterojunction transistors.