Device Geometry and Structural Ordering Enable Faster Infrared Photodetection with Selenium–Iodine

Abstract

The optoelectronic performance of amorphous and partially crystalline semiconductors is strongly governed by device designs and structural disorder, yet studying them in detail to optimize device photo response is challenging. Here, we show that the solid-state optoelectronic response of selenium–iodine (Se–I2) is dictated by obtaining appropriate device geometry and its transformation from a metastable glassy phase into an ordered lamellar structure. Vertically resolved transport measurements reveal pronounced depth-dependent electrical conductivity within Se–I2 films. Immediately after solidification, the glassy Se–I2 network exhibits sluggish carrier transport and persistent photoconductivity. Upon prolonged aging, accompanied by increased structural ordering, the material exhibits enhanced charge transport and millisecond-scale infrared photodetection, with a response time of 4.3 ms. Although the detector was tested under optical modulation frequencies up to 8 kHz, its measured 3–dB bandwidth was 365 Hz. The device also exhibits shot-noise-limited detectivities of ∼108 Jones at 1550 nm and ∼1011 Jones in the visible wavelengths. Spatial photocurrent mapping demonstrates highly uniform carrier collection despite the self-assembled lamellar morphology, while infrared thermal imaging confirms practical imaging capability over a broad temperature range. These results highlight the importance of device geometry and aging-induced structural ordering in optimizing the photo response time for improving response time in selenium-iodine-based semiconductors and identify Se–I2 as a platform for infrared photodetection and thermal imaging.