Ferroelectric-Tunable Photoresponse in α-In2Se3 Photovoltaic Photodetectors: An Ab Initio Quantum Transport Study

Two-dimensional \ensuremath{\alpha}-${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ has drawn broad attention due to its high photoresponse and unique room-temperature interlocked in-plane and out-of-plane ferroelectricity with an ultralow switching electric field. Here, we investigate the photoresponse in a lateral monolayer (ML) \ensuremath{\alpha}-${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ p-i-n junction by using ab initio quantum transport simulations. The maximum photoresponses of the lateral \ensuremath{\alpha}-${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ p-i-n junction are up to 69.2 and 31.6 mA/W for the ferroelectric wurtzite and zincblende phases (shortly named WZ' and ZB') \ensuremath{\alpha}-${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$, respectively, which are 8--17 times higher than that of the extensively researched graphene photodetector (4 mA/W). Remarkably, the ferroelectric photoresponses, defined as the photoresponse change ratio between the two ferroelectric states, of the lateral ML WZ' and ZB'-${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ photodetectors have average values of 127% and 121% with surprising maximum values of $2\ifmmode\times\else\texttimes\fi{}{10}^{6}\mathrm{%}$ and $1\ifmmode\times\else\texttimes\fi{}{10}^{7}\mathrm{%}$, respectively. The physical mechanism comes from the electron density redistribution altered by the atomic displacements due to the polarization switch, rather than the built-in potential change induced by the surface polarization charges. Such ferroelectric-tunable photoresponses in the \ensuremath{\alpha}-${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ photodetector suggest a potential in the fabrication of future optical detection and storage integrated devices.