  Highly sensitive photodetectors with single photon level detection is one of
the key components to a range of emerging technologies, in particular the
ever-growing field of optical communication, remote sensing, and quantum
computing. Currently, most of the single-photon detection technologies require
external biasing at high voltages and/or cooling to low temperatures, posing
great limitations for wider applications. Here, we demonstrate InP nanowire
array photodetectors that can achieve single-photon level light detection at
room temperature without an external bias. We use top-down etched, heavily
doped p-type InP nanowires and n-type AZO/ZnO carrier selective contact to form
a radial p-n junction with a built-in electric field exceeding 3x10^5 V/cm at 0
V. The device exhibits broadband light sensitivity and can distinguish a single
photon per pulse from the dark noise at 0 V, enabled by its design to realize
near-ideal broadband absorption, extremely low dark current, and highly
efficient charge carrier separation. Meanwhile, the bandwidth of the device
reaches above 600 MHz with a timing jitter of 538 ps. The proposed device
design provides a new pathway towards low-cost, high-sensitivity, self-powered
photodetectors for numerous future applications.
