Effect of nitrogen incorporation on surface transfer doping and deep-UV photoresponse in H-terminated diamond MESFETs

Hydrogen-terminated diamond enables solar-blind deep-ultraviolet (DUV) sensing via surface-transfer-doping-induced two-dimensional hole gas (2DHG) channels, yet the quantitative relationship between surface states and nitrogen-related defects and related mechanism of regulating H-termination surface characteristics and MESFET photoresponse performance remains unclear. Here we fabricate H-terminated diamond MESFETs with systematically varied nitrogen incorporation (N/C = 0–6000 ppm) and establish a material-to-device correlation linking surface states, 2DHG modulation, electrical characteristics and photoresponse performance. In this study, nitrogen incorporation alters the epitaxial growth kinetics and the growth mode of diamond layers. Increasing nitrogen defects induce a pronounced negative threshold-voltage shift (-0.27 to −1.92 V) and monotonically degrades the 213 nm photoresponse (responsivity: 60.5–0.007 mA·W −1 , external quantum efficiency: 40.6–0.004% and detectivity: 9.8 ×10 10 –1.7 ×10 7 Jones). This indicates a defect-limited regime where photocarrier coupling/collection is constrained rather than enhanced by gain mechanisms. XPS and UPS results reveal that nitrogen incorporation has an impact on the surface reconstruction of H-terminated diamond, reduces the value of negative electron affinity (NEA: −1.05 ± 0.02 to −0.40 ± 0.14 eV) and weakens attenuating upward band bending. Thereby, 2DHG formation and photocarrier collection is suppressed while defect-assisted compensation/recombination is enhanced.