Platinum (Pt) and palladium (Pd) Schottky diodes on n-type GaN grown by metalorganic chemical vapor deposition were achieved and investigated. Aluminum was used for ohmic contacts. Barrier heights were determined to be as high as ΦB=1.13 eV by the current–voltage (I–V) method and ΦB=1.27 eV by the capacitance–voltage (C–V) method for the Pt/GaN diode, and ΦB=1.11 eV, ΦB=0.96 eV, and ΦB=1.24 eV by I–V, activation energy (I–V–T), and C–V methods for the Pd/GaN diode, respectively. The ideality factors were obtained to be n∼1.10.

We report on the fabrication and characterization of vertical geometry transparent Schottky barrier ultraviolet detectors based on n−/n+-GaN structures grown over sapphire substrates. Spectral responsivity measurements were made using illumination through the UV transparent Schottky barrier metal. A responsitivity as high as 0.18 A/W was measured for wavelengths shorter than the absorption edge of GaN. The detector speed was RC limited and the fall time was 118 ns. The 1/f noise is identified to be the main noise contribution. At 300 Hz, we measure the noise equivalent power at less than 4×10−9 W.

Contacts consisting of various single layer metals to n-type GaN have been formed and characterized. The current-voltage characteristics were measured for 17 different metals (Sc, Hf, Zr, Ag, Al, V, Nb, Ti, Cr, W, Mo, Cu, Co, Au, Pd, Ni, and Pt) deposited on the same epitaxial growth layer. The barrier height, ideality factor, breakdown voltage, and effective Richardson coefficients were measured from those metals which exhibited strong rectifying behavior. The barrier heights for these metal contacts were measured using current-voltagetemperature and capacitance-voltage techniques. It was found that an increase in metal work function correlated with an increase in the barrier height. The surface state density of GaN was approximated to be very similar to CdS and almost a factor of ten less than GaAs.

We report on the dc characteristics and microwave performance of AlGaN/GaN heterostructure field effect transistors in the temperature range from 25 to 300 °C. At temperatures above 200 °C, we observe the temperature activated shunt conductance which is independent of the gate voltage (the activation energy is 0.505 eV). The cutoff frequency and the maximum frequency of oscillations vary from 22 and 70 GHz at 25 °C to 5 and 4 GHz at 300 °C, respectively. The gate leakage current in the range of gate biases from −4 to +1 V is small and nearly proportional to the gate voltage even at 300 °C. At temperatures above 200 °C, the gate leakage current is temperature activated (the activation energy is 0.88 eV). These results show that deep traps strongly affect the AlGaN/GaN characteristics at elevated temperatures.

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