Fabrication of infrared detector with monolithic microlens produced in thermal reflow process

•Development of sub-millimeter base diameter immersion lenses in GaAs for group III-V infrared detectors.•Fabrication process results in lenses with accurate dimensions (330 ± 10 µm clear aperture and 78 ± 6 µm height).•Integration of microlens with the IR detector leads to a three-fold increase in the detector's detectivity.•Uncooled detectors with enhanced detectivity and signal-to-noise ratio achieved through the use of an immersion lens.