Ge-on-Si high efficiency SPADs at 1310 nm

Ge on Si SPAD devices hold promise for cost effective use in vehicular LIDAR [1], quantum optics, quantum communications, and other applications. Previous Ge on SI SPAD devices using mesa structures have shown high dark count rate (DCR) and low single photon detection efficiency (SPDE) [2]. The novel planar device design demonstrated here shows low DCR and high SPDE at short-wave infrared wavelengths. The novel design allows better performance by confining the high field regions using an implanted charge sheet and small top contact region. This design removes the interaction between etched sidewalls and high electric fields seen in mesa devices. We have fabricated devices with a 100 µm diameter charge sheet and a 90 µm diameter top contact. TCSPC measurements were taken at 78 K, 100 K, 125 K, using 1310 nm light with ≪ 1 photon per pulse on average and 50 ns gate times (Fig. 1). A record high SPDE of 38% for Ge-on-Si SPADs was measured for a device temperature of 125 K with an excess bias of 5.5 %, and a record low NEP of 2×10⁻¹⁶WHz⁻¹/² was demonstrated at 78 K.