Effect of AlxGa1-xN buffer layer on the structural and electrical properties of AlGaN/GaN/AlxGa1-xN double heterojunction high electron mobility transistor structures

In this paper, the authors report the effect of the AlxGa1-xN buffer layer on the structural and electrical properties of an AlGaN/GaN/AlxGa1-xN double heterojunction high electron mobility transistor (HEMT). As the Al composition of the buffer layer increased, the two-dimensional electron gas (2DEG) confinement of the channel was shown to improve, which was confirmed by the simulation. The AlGaN buffer HEMT showed improved structural characteristics, such as the surface morphology, crystal quality, and interface roughness compared with the conventional HEMT with a C-doped GaN buffer. A slight decrease in 2DEG characteristics owing to the negative polarization charge was observed. However, in the breakdown voltage characteristics, comparable results were obtained as 652V for the HEMT with C-doped GaN, 624V for the HEMT with an Al0.044Ga0.956N buffer, and 642V for the HEMT with an Al0.088Ga0.912N buffer, although the AlGaN buffers were not doped for semi-insulating.