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.
Photodetectors in the ultraviolet spectral range are of great interest for applications such as fluorescence-free Raman spectroscopy and non-line-of-sight optical communications. These applications require single-photon sensitivity, resulting in the use of intensified CCDs or photomultiplier tubes (PMTs) that are bulky, fragile, operate at high voltages, and/or require active cooling. Silicon carbide avalanche photodiodes (SiC APD) show promise as a compact, rugged replacement, as they exhibit low noise, durability and high gain. In this paper we report on detailed studies of p+-p-i-n SiC APDs operating in both Geiger and linear mode. The single photon detection efficiency (SPDE) of these devices was measured as a function of excess bias using a pulsed 280 nm light emitting diode source focused through a 20 µm pinhole to a spot size <12 µm, with photons per pulse characterized at < 0.5 using a UV enhanced PMT. Devices with 100 µm diameter achieved SPDE > 20% with dark count rate (DCR) of < 700 Hz in both gated and continuous operation. Comparison with linear mode operation shows that avalanche multiplication gain in these devices exceeds 5x106 under these conditions. Examination of linear mode gain vs. applied bias dependence suggests that a sluggish dependence corresponds to a poorer SPDE, which is likely associated with parasitic resistance in these devices. This resistance is consistent with the observed inverse dependence of calculated linear mode gain with increasing optical flux. A peak SPDE of 37% was measured at an excess bias of 3.9 V with a DCR of 7.3 kHz.
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