Ultraviolet single-photon avalanche detectors (UV-SPADs) that are low cost, size, weight, and power as well as resilient to shock, high temperatures and stray magnetic fields have a number of applications. SiC is attractive for UV SPADs as it is inherently blind to visible light, and Geiger mode as well as high-gain linear-mode devices have been demonstrated. However, issues remain regarding bias dependence of spatial uniformity of detection efficiency (DE) and responsivity as well as the temporal resolution, or jitter, in Geiger mode. Over a wide range of device structures (p- vs. n- illuminated) we observe a non-uniform responsivity across the active area for values of gain from 100 to 105, and we observe that the nonuniformity is somewhat reduced at higher gain. The spatial dependence of the DE in Geiger mode agrees with linear-mode results for gain >105. This presents in all devices as an “optically dead” region on one side of the detector whose extent varies with operating conditions and is independent of contact geometry and device layout. The temporal resolution of single-photon detection is characterized with a femtosecond-pulsed source at 267 nm and found to have a full-width-at-half-maximum jitter < 92 ps, which is significantly lower than previously reported results and likely an upper bound due to the quenching circuit and the spatial non-uniformity. Numerical modeling suggests that small variations in doping densities and thicknesses of epitaxial layers might be a cause of the non-uniformity. Results also indicate that detector layer design, size, and geometry can mitigate the effects of spatial non-uniformity,
High sensitivity near-ultraviolet (NUV) avalanche photodiodes operating at wavelengths longer than 300 nm are useful for various applications, including surface exploration of Ocean Worlds and other planetary bodies via Raman spectroscopy. 4H-SiC has long been established as a proven UV detector technology; however, the responsivity of 4H–SiC avalanche photodiodes (APDs) diminishes dramatically at wavelengths longer than ≈ 280 nm due to its weak absorption at wavelengths approaching the indirect bandgap. The authors will present on the design and optimization of 4H-SiC separate absorption, charge and multiplication (SACM) APDs for broadband absorption from 266 to 340 nm.
Kasey Hogan, Sean Tozier, Milena Graziano, Michael Derenge, Michael Shevelev, Vlad Sklyar, Andrew Lang, Kenneth Jones, Mitra Taheri, Woongje Sung, F. Shadi Shahedipour-Sandvik
The advancement in potential selective placement of p-GaN regions places the gallium nitride (GaN) material system on the forefront of next generation power semiconductor devices. The ion implantation technique is commonly used in fabrication of semiconductor devices to achieve high conductivity regions with successful demonstration for n-GaN. This technique has shown little success for post-Mg-implanted activation anneal to achieve p-GaN [1], largely due to the formation of substantial point defects as a result of the implant process. To activate Mg and repair these defects, high annealing temperatures of > 900 °C are required. Considering that GaN dissociates at 840 °C at atmospheric pressure, higher temperature annealing should be performed under a high overpressure of nitrogen and in combination with a protective cap layer.
We report on the results of using a novel Gyrotron annealing technique for Mg implant-activation. Mg implanted GaN layers have been annealed at temperatures and pressures as high as 1300 °C and 40 bar respectively with and without a protective cap. It is observed that Gyrotron annealing at 1100 ˚C for 30 seconds eliminates secondary GaN (0004) Bragg peaks, due to stress relaxation. In addition, skew-symmetric x-ray rocking curves show no stress induced by annealing in the GaN (10-12) peak with FWHM of 59’’, although the GaN (30-32) peak is observed to broaden. We will present an extensive array of characterizations detailing results from Gyrotron annealing, conventional RTA, and high temperature (1300 °C) RTA on similar Mg-implanted, homoepitaxially grown GaN samples.
[1] F. J. Kub et al. Electron. Lett., 50, 3 (2014): 197–198
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