UV Photodetectors

Group-III nitride ternary alloys, particularly gallium nitride (GaN) and its related alloy aluminium gallium nitride (AlGaN) are direct semiconductors with a tunable band gap energy ranging from 3.4 to 6.2 eV. In addition, these semiconductors also possess superior physical properties such as excellent thermal, mechanical, and chemical stability. Therefore, they have been recognized to have the potential for applications in solar-blind UV detectors and sensor devices, particularly for operating under harsh environmental conditions. Although great progress has been achieved in the fabrication of GaN-based devices, UV detectors with cut-off wavelengths between 200 to 365 nm are still in the research and development stage by the academician. For instance, the responsivity at 286 nm for AlGaN/GaN-based solar-blind UV photodetectors is only about 0.05 A/W at 280 nm. Meanwhile, the responsivity for GaN-based UV photodetectors at 360 nm is less than 0.3 A/W. One of the main factors that contributed to the low responsivity is related to the crystalline quality (associated with the stress and dislocation density) of the AlGaN and GaN epilayers, where the large dislocation density in epitaxial layers will result in a large leakage current.

In 2023, unique GaN-based blue LEDs with peak luminous efficacy of 207 lumens per Watt (lm/W), exceeding many industry standards and on par with some of the high-performance LEDs in the global market, were demonstrated by researchers from the Universiti Sains Malaysia (USM) Institute of Nano Optoelectronics Research and Technology (INOR). Leveraging on the growth experience and existing growth recipes, we extend the project into the development of III-nitride based UV detectors where the project aims to develop the next generation of high-performance III-nitride-based UV detectors with responsivity of more than 0.05 A/W at 280 nm. Overall, a few subprojects were designed to achieve this objective. This includes (i) fabrication of GaN-based metal-semiconductor-metal (MSM) UV detectors, (ii) fabrication of Ga2O3/GaN MSM UV detectors, (iii) fabrication of AlGaN/GaN high-electron-mobility-transistor (HEMT) UV detectors, and (iv) UV detectors performance enhancement via plasmonic materials and surface modification.