The optical and structural characteristics of GaN films implanted with Mg and Be ions, grown by low-pressure metalorganic chemical vapor deposition were studied. The low temperature (20 K) photoluminescence (PL) spectra of annealed Mg implanted GaN show a 356 nm near band edge emission, a 378 nm donor-acceptor (D-A) transition with phonon replicas, and a 528 nm green band deep level emission. The origin of the 528 nm green band emission and the 378 nm D-A emission might be attributed, respectively, to the Mg implantation induced clustering defect and the vacancy defect in GaN film. Observations of in-plane and out-of-plane x-ray diffraction spectra for as-grown undoped, Mg implanted and rapid thermal annealed GaN suggest that ion implantation induced anisotropic strain may be responsible for the observed PL emission characteristics.

We carry out an In0.53Ga0.47As/In0.52Al0.48As single photon avalanche diode which exhibits a single photon detection efficiency exceeding 60% at 1310 nm and neat temporal characteristic of 65 ps. A novel concept of dual multiplication layer is incorporated to avoid the tradeoff between dark count rate, afterpulsing and timing jitter, paving the possibility to improve the overall performance of a single photon detector. Based on this elevated device structure, we further optimize the detection efficiency and timing jitter by employing a delicate mesa structure to better confine the electric field distribution within the central multiplication region. For our detector operated under gated mode, a shorten gate width together with an increase of excess bias percentage leads to a significant improvement in the detection performance. We eventually achieve a single photon detection efficiency of 61.4% without the involvement of afterpulsing at the gating frequency of 10 kHz for 200 K.

With 150KeV Mg+ ion implantation, the optical and structural characteristics of GaN films were studied. Post-implant annealing up to 1000°C was performed in N2 ambient with a rapid thermal annealing (RTA) system, without an encapsulation layer. We observed a green band photoluminescence from Mg-implanted GaN. This green band photoluminescence should be associated with Mg induced defect-clustering in GaN. We also use the x-ray diffraction method to study the correlation between structure defects and implantation. We observed an extra shoulder peak at the small angle side of the GaN[0004] diffraction peak. The origin of this shoulder may be attributed to implanted magnesium induced GaN lattice strain.

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The performance of InGaAs/InAlAs single photon avalanche diodes (SPAD) was improved with fabrication in triple mesa. Current SPADs achieve better dark count rate of 5 × 104 ⁄2 for single photon detection efficiency of 31% at RT.