Ga back-graded CuInSe2 thin films for high-performance near-infrared photodetectors

Abstract

Copper indium selenide (CuInSe₂, CISe) thin films are promising materials for optoelectronic applications due to their tunable bandgap, high absorption coefficient, and excellent thermal stability. In this work, the performance of CISe-based photodetectors is enhanced through controlled gallium (Ga) back-side incorporation, forming a compositional grading profile within the absorber layer. The Ga-induced grading improves film crystallinity and grain growth while suppressing recombination losses, leading to enhanced junction quality and carrier extraction. As a result, the optimized Ga-incorporated device exhibits a peak responsivity of 0.67 A W⁻¹ and a specific detectivity (D*) exceeding 10¹² Jones under 1064 nm illumination. In addition, transient photoresponse measurements reveal a significant reduction in response time (τ_10–90%) from 0.48 ms to 0.18 ms, indicating accelerated carrier transport dynamics. Compared with undoped CISe devices, the Ga-graded photodetectors demonstrate improved external quantum efficiency (EQE), reduced series resistance (R_s), and suppressed leakage pathways. These results highlight the effectiveness of Ga back grading in simultaneously optimizing both steady-state sensitivity and temporal response, establishing Ga-graded CISe thin films as promising and cost-effective candidates for high-performance near-infrared (NIR) photodetection and integrated optoelectronic applications.