Effective Mitigation of Persistent Photoconductivity in AlGaN Solar-Blind Field-Effect Phototransistors via In-Situ SiN_x Passivation

AlGaN-based heterojunction field-effect phototransistors featuring high gain and high speed often suffer from serious persistent photoconductivity (PPC). The PPC effect leads to long-term recovery after signal excitation, which not only restricts response speed but also affects the stability and reliability of photoresponse. Herein, in-situ SiNx passivation was used to mitigate the PPC effect in solar-blind AlGaN heterojunction field-effect phototransistors. By the passivation, the decay time constant decreases from 0.79 s and 0.30 s associated with two trap levels to 0.18 s associated with one trap level. Moreover, the response current under periodic weak illumination is significantly stabilized. The device dark current is also reduced by more than one order of magnitude, alongside remarkably improved on-chip uniformity. These improvements are attributed to the reduction of deep acceptor defects on the AlGaN surface by the in-situ SiNx passivation.