Platinum was deposited on unintentionally doped n-Al x Ga 1-x N films grown by metal-organic chemical vapor deposition (MOCVD) to form MSM ultraviolet photodetectors. All devices were annealed for 10 min at different temperature in N 2 ambient. Results indicate that the generation of hillocks on the surface of Pt thin-film electrodes at the elevated temperatures due to relieving compressive stress affects the dark current directly. Dark current less than 10pA in the (-10V,10V) range was obtained from a device after annealing at 900 º C. Both detectors show sharp spectral responsivity cutoff of about three orders of magnitude by 325nm and 315nm respectively.
Capacitance-voltage and capacitance-frequency characteristics of Al0.42Ga0.58N∕Al0.40Ga0.60N heterojunction p-i-n photodiode are investigated. The slopes of the 1∕C2-V plot were nearly the same at 100Hz, 1KHz, 10KHz, and 100KHz, slightly smaller at 1MHz. A depletion region width of 63.6nm calculated under zero bias for this diode was smaller than that of the intrinsic region, which showed that the intrinsic region was depleted partly under zero bias. The difference between the capacitance measured at low and high frequencies could be due to the high resistivity of the intrinsic region.
Temperature dependence on electrical characteristics of a Ni∕Au–Al0.45Ga0.55N Schottky photodiode is investigated in a temperature range of 198–323K. The ideality factor decreases from 2.57 to 1.75, while the barrier height increases from 0.75to1.14eV in this temperature range. The ln(I)-V curves at a small forward current are intersectant at 273, 298, and 323K and are almost parallel at 198, 223, and 248K. This crossing of the ln(I)-V curves is an inherent property of Schottky diodes, and the almost parallel curves can be well explained by thermionic field emission theory.
Photodiodes designed to be sensitive in the region 1.4-1.7 μm and obtained by vacuum magnetron sputtering of the Pt layer on the surface of the HgInTe single crystal are studied. Temperature dependence on electrical characteristics of the Schottky diodes was investigated in a temperature range from 120 K to 260 K. The current-voltage characteristics of the diodes show excellent rectification behavior. Temperature dependence on the ideality factor and apparent barrier height was determined, including the effect of series resistance. The ideality factor evaluated was observed to decrease from 2.93 to 1.42, while the flatband barrier height was 0.46 eV in this temperature range. The temperature dependence of the forward characteristics can be well explained by thermionic emission theory. The flatband Schottky barrier height for Pt on Hg 3 In 2 Te 6 is smaller than the value reported for both ITO and Au rectifying contacts on this material. A possible mechanism of the correlation of the ideality factor and barrier height has been proposed.
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