Unraveling the Mechanism of the Persistent Photoconductivity in InSe and its Doped Counterparts

Dopant levels in layered compound InSe have considerable potential in optoelectronic devices. Dopant-induced trap states are essential in determining the optoelectrical properties of semiconductors. However, detailed studies of the persistent photoconductivity (PPC) and related mechanism in doped InSe are still not available. Here, the dependence of excitation energy on the shallow donor level caused by the dopants (Ge, Sn) in InSe is systematically investigated. Notably, prolonged decay time originates from extrinsic Ge, Sn dopants and these doping-assisted states improve the optoelectrical performance of pristine InSe. Those photogenerated carriers are trapped in the Ge, Sn shallow impurities states, which are long-lived enough to be extracted into Au contacts before annihilation. This renders Ge-, Sn-doped InSe photoconductive gain and maximized photocurrent. Sn-doped InSe single crystal device can achieve a maximum responsivity of around 1.7 x 10(6) A W-1 under red light and detectivity of 6.18 x 10(13) Jones. In addition, Hall measurements identify the carrier concentration and the Hall mobility of pristine InSe is significantly changed by Ge and Sn dopants. It is demonstrated that doping Ge, Sn atoms is responsible for the obvious photoconductivity and beneficial for the high-performance photodetector, offering intriguing opportunities for novel holographic memory applications.