Energy band alignment and interface states in AlGaN/4H–SiC vertical heterojunction diodes

The effects of AlxGa1−xN aluminum fraction x and SiC surface pre-treatment on AlGaN/4H–SiC heterojunction interfaces are experimentally investigated. From capacitance vs. voltage measurements, the conduction band offsets are found to be ΔEC ≈ 0.30 for x ≈ 0.3 and ΔEC ≈ 0.56 for x ≈ 0.5. Forward bias ideality factors are reasonable at 3.3 for Al0.3Ga0.7N diodes, but >9 for Al0.5Ga0.5N diodes, suggesting a higher level of interface charge related to the higher aluminum fraction. Reverse bias leakage is acceptably low, with breakdown occurring at VA > 200 V reverse bias for all tested devices. The effect of 1500 °C hydrogen etching of the SiC substrate prior to AlxGa1−xN growth is also investigated, and found to have little effect for x = 0.3 but a beneficial effect for x = 0.5.