Magneto-tunability of photocurrent in p-Si (100)/NiFe2O4/SL/CuPc/Al [where, spacer layer (SL)=P3HT and rGO] heterojunction devices at room temperature: Role of organic interface in Opto-spintronics

Abstract

Investigation of carrier transportation at ferromagnetic (FM)/organic semiconductor (OSC) interface has great research potential for the formation of spin valve (SV) device. Magneto-optical coupling effect on carriers has been investigated in FM/OSC based two heterostructures Silicon (Si)/Nickel ferrite (NiFe₂O₄)/poly (3-hexylthiophene) (P3HT)/Copper Phthalocyanine (CuPc)/Aluminium (Al) [P3HT based i.e., S1 heterostructure] and Si/NiFe₂O₄ (NFO)/reduced graphene oxide (rGO)/CuPc/Al [rGO based i.e, S2 heterostructure]. Direct spin injection and carrier transport mechanism are found to be prominent at the NFO/rGO interface due to very close position of conduction bands of NFO and rGO to the Fermi energy level, which results larger device current (1000 times larger than S1) in S2 sample. The S1 heterostructure exhibits a drastic increase in negative magnetoresistance (MR)at low magnetic field (H_ext) regime due to enhancement of both de-pining spin from weak potential well and spin dependent tunneling of carriers at NFO/P3HT interface. However, at high H_ext organic magnetoresistance (OMAR) effect of P3HT polymer results overall decrease of negative MR of S1 sample. In contrast, S2 device shows monotonic increase in negative MR. A significant photoresponse under 660 nm red laser has obtained in both the heterostructures. At high optical power, switching of MR from negative to positive value has been observed in both the devices, which attributes substantial scattering and decoherence of photogenerated carriers. Another side, on switching of H_ext a drastic decrease and a monotonic decrease of photocurrent has been observed in S1 and S2 heterostructures, respectively, which comes from the modification of spin transportation at the interface.