Deep ultraviolet monolayer GaN/AlN disk-in-nanowire array photodiode on silicon

Extreme confinement of carriers in GaN layers of thickness of the order of a monolayer leads to a large quantum confinement energy and very large electronic and optical bandgaps. We have exploited this to realize a photodiode with AlN nanowire arrays, grown on silicon substrates by plasma-enhanced molecular beam epitaxy, wherein multiple ∼2 monolayer disks are inserted as the light absorbing region. Photoluminescence and photocurrent spectra confirm the optical gaps of the monolayer GaN. The photocurrent spectra show a peak at ∼240 nm in the deep-ultraviolet region of the optical spectrum. The dark current of the photodiodes is ∼10 nA at −6 V at room temperature. The peak quantum efficiency is 0.6%, and the noise-equivalent power is estimated to be 4.3 × 10−11W/Hz1/2. The bandwidth of the device is estimated to be limited to ∼3 MHz by the series resistance and diode capacitance.