Current–Voltage Characteristics of AlN/GaN Heterostructure Metal Insulator Semiconductor Diode

We fabricated heterostructure metal insulator semiconductor (Hetero-MIS) diodes with a Schottky metal-(Ni/Au)/AlN(6 nm)/n+-GaN(Si:3×1018 cm-3)/ohmic metal-(Ti/Al/Pt/Au) structure, and measured the dependence of current–voltage (I–V) characteristics of the diodes on the growth temperature of the AlN layer using low-pressure metalorganic chemical vapor deposition (MOCVD). We found that the current decreases as the growth temperature of the AlN layer decreases from 990°C to 650°C. We conclude that the current flows mainly between the columnar crystals of the AlN layer, because we found from the temperature dependence of the surface morphology of the AlN layer that the radius of the columnar crystals decreases and the height of the columns decreases as the growth temperature decreases, and because the measured I–V characteristics are in agreement with the simulated ones if we assume that the thickness of the AlN layer is about 2 nm, which is much less than the measured thickness of the columnar crystal of 6 nm.