The design, modeling, fabrication, and characterization of single-photon avalanche diode detectors with an epitaxial Ge absorption region grown directly on Si are presented. At 100 K, a single-photon detection efficiency of 4% at 1310 nm wavelength was measured with a dark count rate of ∼6 megacounts/s, resulting in the lowest reported noiseequivalent power for a Ge-on-Si single-photon avalanche diode detector (1 × 10 −14 WHz −1/2 ). The first report of 1550 nm wavelength detection efficiency measurements with such a device is presented. A jitter of 300 ps was measured, and preliminary tests on after-pulsing showed only a small increase (a factor of 2) in the normalized dark count rate when the gating frequency was increased from 1 kHz to 1 MHz. These initial results suggest that optimized devices integrated on Si substrates could potentially provide performance comparable to or better than that of many commercially available discrete technologies.Index Terms-Detector, germanium on silicon, single-photon avalanche diode, single-photon counting.
Gunn oscillations have been observed and modelled, using a Monte Carlo method, in planar semiconductor GaAs/AlGaAs heterostructure diodes. Our simulation results support an interpretation of experimental results whereby the Gunn domains travel parallel to the semiconductor layers, as opposed to perpendicular to the layers in traditional vertical devices. Fabricated devices with contact separations of 4 µm down to 1.3 µm have been found to oscillate over a range of frequencies from 24.5 GHz to 108 GHz. These structures offer the prospect of generating frequencies further into the terahertz range and an increased ease of integration and flexibility over equivalent traditional vertical structures.
The performance and operation of GaN Gunn diodes has been investigated for a number of device structures and at various temperatures using a three-valley Monte Carlo model incorporating the heat diffusion equation. Simulated structures include both notched and uniform transit regions, with the performance of each also observed at fixed temperatures from 350 to 500 K. Finally, the long-term function of an ideal GaN Gunn diode was simulated to observe the effect of temperature increases as a result of operation, and to estimate the time it would take the device to cool sufficiently to allow unlimited cycles of pulsed operation. It was found that in order to obtain ∼300 GHz operation, the optimum device structure required a notched transit region. Significantly, it was also found that the longer term effect of heat on the device performance, with respect to the device frequency over each cycle, was considerable, a result which raises fundamental questions as to the viability of such devices.
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