InGaAs/InAlAs Single Photon Avalanche Diode at 1550 nm

Single photon detectors sensitive to near-infrared (NIR) wavelength light are used in an increasing number of applications, such as quantum key distribution, laser detection and ranging, and integrated circuit analysis. There are many types of NIR single photon detectors, e.g. photomultiplier tube, superconducting single photon detector and single photon avalanche diode (SPAD). However, the SPAD remains the most practical of them, mainly because of their relatively high operating temperatures (~ 220 K to room temperature), hence requiring only moderate or no cooling. Most NIR SPADs are InGaAs/InP SPADs, which are sensitive to 1550 nm wavelength light. An InGaAs and an InP layer are used as absorption and avalanche materials, respectively. The main performance parameters for SPADs are Single Photon Detection Efficiency (SPDE), Dark Count Rate (DCR), and After-pulsing probability. Simulations [1] have shown that, for a given DCR, SPADs using InAlAs instead of InP as avalanche material achieve higher SPDE, because of higher avalanche breakdown probability (proportional to SPDE) in InAlAs than in InP. Thus SPADs based on InAlAs can potentially achieve higher operating temperature, compared to SPADs based on InP, for given SPDE and DCR. Moreover, breakdown voltage of InAlAs is less sensitive to temperature than InP is [2], offering greater flexibility in the SPAD operation temperature. In this work we report a 50 m diameter InGaAs/InAlAs SPAD for detection of 1550 nm photons. The InGaAs/InAlAs SPAD was grown by molecular beam epitaxy (MBE) and fabricated using standard photolithography and wet chemical etching. The SPAD was characterised in gated mode inside a low temperature probe station. Photons were from a heavily attenuated pulsed laser (20 ps FWHM pulse width). DCR data versus overbias, Vob, at different temperatures and SPDE at 210 K are shown in Fig. 1(a). From 293 to 210 K, DCR reduced by ~ 2 orders of magnitude and a maximum SPDE of 41% was achieved. Despite the relatively large device diameter, these results are significantly better than previous reports of InGaAs/InAlAs SPADs [3-5] as shown in Fig. 1(b).