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A simple random ionization path length model is used to investigate the breakdown probabilities and jitter in single photon avalanche diodes (SPADs) with submicron multiplication widths. The simulation results show that increasing the multiplication width may not necessarily increase the breakdown probability relative to the breakdown voltage, as the effect of dead space becomes more dominant in thinner multiplication regions at realistic ionization threshold energies for GaAs. On the other hand, reducing the multiplication width results in smaller breakdown time and jitter, despite the increased dead space. The effect of dead space in degrading breakdown time and jitter is relatively weak and further compensated by the stronger influence of large feedback ionization at high fields. Thus, SPAD designs that can minimize the dark count rate may potentially benefit from enhanced breakdown probability, breakdown time, and jitter by reducing the thickness of the multiplication region.

a b s t r a c tNiFe film was pulse electrodeposited on conductive Cu substrate under galvanostatic mode in the presence of an ultrasonic field. The NiFe film electrodeposited was subjected to structural and surface analyses by Xray diffraction, energy dispersive X-ray spectroscopy, surface profiling and scanning electron microscopy, respectively. The results show that the ultrasonic field has significantly improved the surface roughness, reduced the spherical grain size in the range from 490-575 nm to 90-150 nm, and increased the Ni content from 76.08% to 79.74% in the NiFe film electrodeposited.

Nickel iron (NiFe) thin films were prepared on the copper substrate by ultrasonic assisted pulse electrodeposition under galvanostatic mode. Careful control of the thin films deposition is essential as the electrical properties of the films could be greatly affected, particularly if low quality films are produced. The preparation of NiFe/Cu thin films was aimed to reduce the grain size of NiFe particles, surface roughness and electrical resistivity of the copper substrates. Various parameters were systematically studied including current magnitude, deposition time and ultrasonic bath temperature. The optimized conditions to obtain NiFe permalloy, which subsequently applied to all investigated samples, were found at a current magnitude of 70 mA deposited for a duration of 2 min under ultrasonic bath temperature of 27 °C. The composition of NiFe permalloy was as close as Ni 80.71% and Fe 19.29% and the surface roughness was reduced from 12.76 nm to 2.25 nm. The films electrical resistivity was decreased nearly sevenfold from an initial value of 67.32 μΩ cm to 9.46 μΩ cm.