UC Berkeley

Semiconducting absorbers in high-performance short-wave infrared (SWIR) photodetectors and imaging sensor arrays are dominated by single-crystalline germanium and III-V semiconductors. However, these materials require complex growth and device fabrication procedures. Here, thermally evaporated Se_x Te_{1- x} alloy thin films with tunable bandgaps for the fabrication of high-performance SWIR photodetectors are reported. From absorption measurements, it is shown that the bandgaps of Se_x Te_{1- x} films can be tuned continuously from 0.31 eV (Te) to 1.87 eV (Se). Owing to their tunable bandgaps, the peak responsivity position and photoresponse edge of Se_x Te_{1- x} film-based photoconductors can be tuned in the SWIR regime. By using an optical cavity substrate consisting of Au/Al₂ O₃ to enhance its absorption near the bandgap edge, the Se_0.32 Te_0.68 film (an optical bandgap of ≈0.8 eV)-based photoconductor exhibits a cut-off wavelength at ≈1.7 μm and gives a responsivity of 1.5 AW^-1 and implied detectivity of 6.5 × 10¹⁰ cm Hz^1/2 W^-1 at 1.55 μm at room temperature. Importantly, the nature of the thermal evaporation process enables the fabrication of Se_0.32 Te_0.68 -based 42 × 42 focal plane arrays with good pixel uniformity, demonstrating the potential of this unique material system used for infrared imaging sensor systems.