Synergistic Effect of Surface States and Deep Defects for Ultrahigh Gain Deep‐Ultraviolet Photodetector with Low‐Voltage Operation

Abstract To achieve ultra‐high gain deep‐ultraviolet (DUV) detectors based on ultra‐wide bandgap semiconductors comparable with those of bulky photomultiplier tubes (PMTs), avalanche photodiodes have usually been adopted. However, the high‐operation voltage (∼100 V) is not compatible with monolithic integration. Herein, it is demonstrated that the ultra‐high gain DUV photodetectors (PDs) with low operation voltages (<5 V) can be achieved by using the synergistic effect of surface states and deep defects in a type‐Ib single‐crystal diamond (SCD) substrate. The overall photoresponse, such as the sensitivity, dark current, spectral selectivity, and response speed, of the diamond DUV‐PDs can be simply tailored by the surface hydrogen or oxygen termination of the SCD substrate. The DUV responsivity and external quantum efficiency are more than 2.5 × 10⁴A/W and 1.4 × 10⁷%, respectively, at 220 nm‐wavelength light, comparable with those of PMTs. The DUV/visible light rejection ratio (R_{220 nm}/R_{400 nm}) is as high as 6.7 × 10⁵. The depletion of the 2D hole gas by deep nitrogen defect provides a low dark current and the filling of the ionized nitrogen upon DUV illumination induces a huge photocurrent. The synergistic effect of the surface states and the bulk deep defects opens the avenue for the development of DUV detectors compatible with integrated circuits.