Lab-built flexible near-infrared sensor boosts response 5.1-fold

Bend a sensor repeatedly and its promise meets a physical test: does the signal survive? At the Korea Institute of Materials Science, a team led by principal researcher Jung-Dae Kwon, with Yonghun Kim and Jongwon Yoon, built a flexible near-infrared photodetector whose photoresponsivity increased approximately 5.1-fold compared with a conventional structure. After 4,000 bending cycles, it retained more than 90% of its initial response.

Near-infrared light is invisible, but it can penetrate skin and biological tissue relatively effectively. That makes it useful for heart-rate and blood-oxygen monitoring, medical diagnostics, night imaging and optical communications. The team says current wearable sensors often rely on rigid silicon detectors mounted on flexible substrates, while organic semiconductors and quantum dots bring durability or environmental-stability limitations.

The KIMS device uses a heterojunction, a junction between two semiconductor materials, combining n-type hydrogenated amorphous silicon with tellurium. Tellurium absorbs near-infrared light and generates charge carriers; the amorphous silicon helps move them toward an electrode. The researchers also controlled phosphorus doping to reduce defects and added a front-surface-field layer, which guides carriers more efficiently and limits electron–hole recombination, a source of signal loss.

The detector maintained light detection across 400 to 1,600 nanometers. Its detectivity, a measure of how well a detector can distinguish weak light signals, rose 2.6-fold versus the conventional structure. The researchers achieved those gains by optimizing the silicon's material quality and the device's internal electric field, rather than introducing a new light-absorbing material or additional complex fabrication processes.

So what changes in practice? A detector that remains responsive while bending could fit more closely onto skin or curved surfaces, supporting wearable health-care devices, medical diagnostic sensors and optical communication receivers. Its inorganic materials are compatible with conventional CMOS manufacturing processes, which KIMS says makes large-area fabrication suitable; the report describes a research result.