Trap-Mediated Photogating in Hybrid Organic-Inorganic Heterojunction Phototransistors for Photo-Memory and Photodetection

Abstract

Trap-mediated photocarrier dynamics fundamentally govern the photoresponse of hybrid organic–inorganic heterojunction phototransistors. In phototransistors with type-II heterojunctions, photoinduced electron transfer from the organic layer to the channel leaves holes trapped in the organic layer, inducing photogating that modulates channel conductance. Depending on trapping kinetics, these devices can function as fast photodetectors or light-programmable synaptic memories. We develop a compact, physics-based current-to-charge conversion model that quantitatively links transient drain current to trapped-hole density. The model incorporates shallow and deep trap populations with distinct kinetics and introduces a closed-form recurrence relation to describe conductance evolution under pulsed illumination. Validated on TIPS-Tc/IGZO and TES-ADT/IGZO phototransistors, the model accurately reproduces single- and multi-pulse responses and yields physically meaningful trap parameters. Deep-trap dominance in TIPS-Tc enables long retention and near-linear synaptic plasticity, whereas TES-ADT, dominated by shallow traps, exhibits a rapid photodetection response. In the TIPS-Tc/IGZO device, gate-voltage polarity modulation further allows programmable switching between memory retention, natural relaxation, and active forgetting by controlling charge distribution and trapping kinetics in the organic layer, thereby tuning the photogating strength. The deep-to-shallow trap ratio is identified as a key figure of merit governing the trade-off between retention, linearity, sensitivity, and speed. Requiring only minimal transient measurements and providing kinetically interpretable parameters, the model offers a predictive tool for material screening, device optimization, and array-scale design of light-programmable optoelectronic memory and high-speed photodetector systems.