Effects of carrier mobility and morphology in organic semiconductor spin valves

TL;DR

This study investigates how carrier mobility and morphology influence spin transport in organic semiconductor spin valves, highlighting the importance of interface quality and demonstrating room-temperature magnetoresistance in certain OSCs.

Contribution

It reveals that interface roughness affects spin transport more than carrier type or mobility, emphasizing the need to optimize FM/OSC interfaces for better spintronic device performance.

Findings

Magnetoresistance observed up to room temperature in Alq3 and CuPc devices.

High mobility OSCs with rougher surfaces show weaker spin transport effects.

Interface roughness correlates with degradation of spin transport.

Abstract

We studied spin transport in four organic semiconductors (OSCs) with different electronic properties, with Fe and Co as the top and bottom ferromagnetic (FM) contacts, respectively. Magnetoresistance (MR) effects were observed up to room temperature in junctions based on an electron-carrying OSC, tris(8-hyroxyquinoline) aluminum (Alq$_3$) and a hole-carrying OSC, copper phthalocyanine (CuPc). The MR shows similar temperature dependence for these two OSCs, which suggests that the FM leads rather than the OSCs play a dominant role on the spin-transport degradation with increasing temperature. We also investigated junctions based on two high lateral mobility electron-carrying OSCs, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and N, N'-bis(4-trifluoromethylbenzyl)-1,4,5,8-naphthalenetetracarboxylic diimide (CF$_3$-NTCDI). However, these junctions showed much weaker spin transport effects. Morphological studies suggest that these high mobility OSC films have much rougher surfaces than either Alq$_3$ or CuPc, therefore the degradation of spin transport may originate from enhanced scattering due to the rougher FM/OSC interfaces. Our study shows that FM/OSC interfaces play an important role for spin transport in organic devices and need further exploration.