Capacitance analysis of Al0.25Ga0.75N/GaN heterostructure barrier varactor diodes

The capacitance-voltage (C-V) characteristics of Al0.25Ga0.75N/GaN heterostructure barrier varactors (HBV) grown by metal-organic chemical vapor deposition on a c-oriented sapphire substrate were studied. The favorable material properties of wide-band-gap III-N's are important in realizing the HBVs for frequency triples and distributed line pulse sharpens for practical use. The HBV structure consists of a 10-nm-thick undoped Al0.25Ga0.75N barrier sandwiched between two undoped GaN layers with a thickness of 5 nm. The barrier structure is further sandwiched between two n-GaN (n = 5 x 10(17) cm(-3)) layers with respective thicknesses of 500 nm and 1 mu m to form the top and the bottom ohmic contacts. At room temperature, the C-V characteristics show a maximum capacitance C a at approximately -1.8 V because of the induced piezoelectric field within the heterostructure, and the TV characteristics show an increase in leakage current below -1.5 V and above 0.5 V.