Advanced Wide-Bandgap Semiconductor Ultraviolet Photodetectors for Enhanced Detection and Imaging

Ultraviolet (UV) rays, situated on the electromagnetic spectrum just beyond visible light, are incredibly important in our lives. Comprising UVA, UVB, and UVC rays, they have distinct roles, both beneficial and potentially harmful. UVB rays, for instance, facilitate the synthesis of vitamin D in our skin, vital for our overall health. Moreover, moderate exposure to UVA and UVB rays can promote skin health.

On the flip side, UVC rays, while the most dangerous, are fortunately absorbed by the Earth's atmosphere, serving as a natural shield against these harmful rays. Therefore, it is vital to have ultraviolet photodetectors which are designed to convert UV light into electrical signals, which are pivotal in diverse fields. They play a central role in UV radiation monitoring, contributing to public safety by assessing UV exposure risks, and are instrumental in environmental monitoring, helping scientists understand the impact of UV radiation on ecosystems. Furthermore, UV photodetectors are essential in astronomy for observing celestial phenomena beyond Earth's UV-absorbing atmosphere and are indispensable tools in medical research, where they enable insights into molecular processes through fluorescence microscopy and DNA analysis. In addition, they have crucial roles in water and air purification by ensuring efficient UV-C disinfection and contributing to safer water and air for consumption and breathing.

In the early days, UV detection was primarily done via thermal detectors, charged coupled devices and photomultiplier tubes, however, these devices were inefficient, slow, fragile, bulky and had wavelength independent response. Therefore, new and improved semiconductors like silicon-based UV photodiodes and GaAs-based photodiodes proved to be a better option mainly due to their low cost, lightweight, insensitiveness to magnetic field and faster response. However, Si-based UV photodiodes show some limitations typically due to the building up of the passivation layer which reduces the quantum efficiency over time in the gaping UV range, and device ageing mostly because of overexposure to high energy radiation. Moreover, Si-based photodiodes must have a cool active surface in order to reduce dark current, however, this attracts contaminants which can lower detectivity.

On the other hand, UV photodetectors based on wideband gap semiconductors like Sic, diamond and III-nitrides proved to be a superior alternative, by having room temperature operation and intrinsic visible blindness. Figure 1 compares the key parameters of various materials used in UV photodetectors and proves that WBG semiconductor-type material has better overall characteristics.