N-polar AlN buffer growth by metal–organic vapor phase epitaxy for transistor applications

We present the electrical characterization of N-polar AlN layers grown by metal–organic vapor phase epitaxy and the demonstration of N-polar AlN-channel metal–semiconductor field-effect transistors (MESFETs). A high concentration of silicon is unintentionally incorporated during the high-temperature growth of N-polar AlN, causing a high buffer leakage current. The silicon concentration decreases from 2 × 10 18 to 9 × 10 15 cm −3 with decreasing growth temperature, reducing the buffer leakage current to 5.6 nA/mm at a 100 V bias. The N-polar AlN MESFET exhibits an off-state drain current of 0.27 nA/mm and a transistor on/off ratio of 4.6 × 10 4 owing to the low leakage of AlN buffer layers.