Dual-surface lens with ring-shaped structures for optical tuning of GaN ultraviolet photodetectors at low temperature

Abstract

This study aims to enhance the optical sensitivity of gallium nitride ultraviolet (UV) photodetectors at low temperatures using a multifunctional microlens with ring-shaped structures. This dual-surface lens with ring-shaped structures (i.e., DSLR), a unique microlens, was fabricated by employing a curable polymer and three-dimensional printed mold, and it has two primary regions: An upper and a lower region. The upper region of the DSLR serves as a smooth lens surface to focus the incident UV rays by delaying frost formation at low temperatures. The lower region captures condensed water droplets, thus allowing for only local frost formation. When compared to a photodetector without the DSLR, the photodetector covered by the DSLR generated a higher photocurrent at low temperatures (corresponding to a ∼13.85% increase in generated photocurrent in the temperature range of −20 °C to −1.2 °C). Thus, the findings of this study support the use of a facile, cost-effective, and multifunctional dual-surface polymer lens for higher-sensitivity UV detection in various low-temperature environments, such as the Arctic, outer space, and the environment within cryostats.