An Ultra-Thin Ultraviolet Enhanced Backside-Illuminated Single-Photon Avalanche Diode With 650 nm-Thin Silicon Body Based on SOI Technology

We present the world's thinnest backside illuminated (BSI) single-photon avalanche diode (SPAD) with a silicon (Si) thickness of 650 nm fabricated in complementary metal-oxide-semiconductor (CMOS) compatible silicon-on-insulator (SOI) technology. The well-optimized doping profile is exploited in this square-shaped BSI SPAD with ultrathin Si body consisting of n
⁺⁺
/p-well and n-well guard ring (GR) to outstandingly improve detection efficiency in ultraviolet (UV) spectral range. This BSI SPAD exhibits a low leakage current (≈0.1pA) and a low breakdown voltage (8.5V) at room temperature (RT). A low dark count rate (DCR) of 156.8cps/μm
²
at 3V excess bias is estimated at RT. A peak quantum efficiency (QE) of 96.41% is also measured under a wavelength of 423 nm at 4V. This BSI SPAD indicates a peak photon detection probability (PDP) of 69.51% upon a wavelength of 423 nm at 3V excess bias. A significant expansion of the UV sensitivity down to a wavelength of 291 nm is represented with a PDP of 15.56% at 3V excess bias. To the best of our knowledge, the detection efficiency of this ultrathin BSI SPAD in the UV wavelength regime down to 291 nm is the best result ever reported for Si-based BSI SPAD in spite of the absence of an integrated CMOS circuitry.