Study on GaN-based semiconductor devices for radiation-optical conversion detection

[Background] Gallium nitride (GaN) exhibits exceptional optoelectronic properties, making it highly suitable for applications in high-power devices, light-emitting diodes (LEDs), high-electron-mobility transistors (HEMTs), and radiation detectors. Particularly in radiation detection, GaN can function as both a semiconductor and a scintillator. As a scintillator material, it demonstrates high luminescence efficiency. However, the yellow luminescence band induced by defects in the material often leads to slow time response, limiting its broader application. On the other hand, GaN-based LEDs with multi-quantum well (MQW) structures can achieve excellent electroluminescence performance. Nevertheless, MQW-enhanced scintillators generally suffer from drawbacks such as a thin sensitive layer and low energy deposition efficiency. [Purpose] To leverage the advantageous properties of GaN comprehensively and achieve higher overall performance in detection, this study proposes a radiation-to-optical conversion detection mode that combines GaN semiconductor devices for simultaneous radiation energy deposition and carrier recombination luminescence. By constructing a PN junction structure incorporating MQWs on a high-resistivity, high-mobility GaN substrate, a radiation detection device capable of both radiation-to-carrier conversion and carrier recombination luminescence is realized. [Methods] A 400 μm-thick unintentionally doped high-resistivity GaN single crystal was used as the radiation energy deposition layer. A PN junction structure with MQWs was epitaxially grown on the high-resistivity GaN substrate via metal-organic chemical vapor deposition (MOCVD). The epitaxial layer was segmented into independent regions using inductively coupled plasma (ICP) etching. Transparent indium tin oxide (ITO) electrodes were subsequently fabricated via magnetron sputtering, followed by the deposition of metal electrodes on both the top and bottom surfaces of the device. [Results] The device exhibited low dark current and sensitive X-ray response characteristics. A multi-quantum well recombination structure with a luminescence peak at 410 nm was incorporated into the device. Luminescence spectrum tests and imaging analysis confirmed the device’s response to varying radiation doses and changes in luminescence efficiency under different applied voltages. [Conclusions] The designed device enables directional drift and recombination luminescence of carriers generated by radiation energy deposition under an applied electric field. By leveraging semiconductor device design and electric-field-regulated carrier behavior, the luminescence efficiency, response time, and emission spectrum of the device can be effectively modulated. This approach offers a novel technical pathway for radiation detection.