Electric Field and Temperature Dependent Circular Photogalvanic Effect in Methylammonium Lead Iodide Microcrystals FETs*

One of the most promising materials in the renewable energy industry is the halide perovskite CH3NH3PbI3 (MAPI). MAPI is known for its efficient conversion of light into long-lived charged carriers, which may be attributed to the formation of indirect spin-polarized sub-bands. Circular photogalvanic effect (CPGE) measurements sensitively probe these spin-polarized states, believed to originate in MAPI due to the Rashba effect. However, whether such an effect occurs at the surface or inside the bulk activated by thermal fluctuation is still under debate.

We analyze the CPGE in MAPI microcrystal FETs with energetic and spatial resolutions at various temperatures. Our results show a strong CPGE signal at 80 K, challenging the thermally induced Rashba effect explanation. Additionally, a sudden polarity change in the CPGE signal just below the bandgap energy could potentially involve exciton formation. Likewise, reversing the source-drain bias results in CPGE polarity shifts, which can be attributed to the Edelstein effect. Furthermore, our spatial-resolved CPGE indicates a long spin diffusion length in this material. We further show the impact of ion migration and gate tuning on CPGE, which can suppress the helicity-dependent photocurrent.