Polymer PBT/n-GaN metal–insulator–semiconductor structure

Organic poly(p-phenylenebenzobisthiazole), PBT, is spin coated on n-GaN epilayer to serve as a gate insulating layer. The GaN is grown on c sapphire by the metalorganic-chemical-vapor-deposition method. A metal-insulator-semiconductor structure is fabricated with Al ohmic contact to the n-GaN, and Au/Al gate metal on top of the PBT. High-frequency capacitance measurements are performed. A doping concentration of 8.2×1016 cm−3 is obtained from the capacitance in the depletion region as compared with a Hall value of 7.8×1016 cm−3. Another technique of max–min capacitance method is also used in the calculation of the doping concentration. The threshold voltage is calculated as −5.1 V, and negative charges with an effective charge number density of 9.3×1011 cm−2 shift the capacitance curve towards the positive voltage side. The hysteresis phenomenon is observed and analyzed. The current–voltage curve shows a low, constant current value up to 20 V.