【Member Papers】Wide-bandgap Ga₂O₃ single crystal-based heterojunctions with organic interlayers for high-performance x-ray detection

      Researchers from the Wuhan University have published a dissertation titled "Wide-bandgap Ga₂O₃ single crystal-based heterojunctions with organic interlayers for high-performance x-ray detection" in Applied Physics Letters.

Background

      X-ray detection plays a pivotal role in diverse and multiple fields, including medical imaging, industrial nondestructive testing, space exploration, scientific research, and national security. The device performance in these applications is fundamentally governed by the properties of the semiconductor materials serving as the active sensing layers. Ideal materials require high sensitivity to ionizing radiation, efficient charge collection efficiency (CCE), excellent energy resolution, and thermal stability. Conventional semiconductors like silicon (Si) and germanium (Ge) possess relatively narrow bandgaps (1.12 and 0.67 eV, respectively). This inherent property leads to significant limitations: high intrinsic carrier concentrations at room temperature, resulting in substantial leakage currents and noise that degrade the signal-to-noise ratio and energy resolution, particularly for low-dose or low-energy x-ray detection. Furthermore, their lower critical breakdown electric field strength limits the maximum applicable bias voltage, constraining achievable sensitivity and charge collection efficiency. Wide bandgap semiconductors (WBGSs), such as silicon carbide (SiC) and gallium nitride (GaN), offer significant improvements regarding these issues, enabling room-temperature operation with lower leakage currents and enhanced radiation tolerance. For more advanced applications, it is the quest for materials exhibiting even greater robustness and performance for next-generation, high-flux, or high-energy x-ray detection.

Abstract

      Gallium oxide (Ga₂O₃) exhibits significant potential for next-generation x-ray detection due to its excellent optoelectronic properties. However, x-ray detectors based on β-Ga₂O₃ single crystals scarcely reported, mainly because fabricating p-type Ga₂O₃ remains challenging. In this work, unintentionally doped and Fe-doped β-Ga₂O₃ single crystal wafers have been systematically investigated for x-ray detection using a heterojunction strategy with organic interlayers. The device performance has been carefully evaluated, achieving high response speed (<0.1 s), low dark current (0.42 nA at −40 V), excellent device stability (stable photoresponse over 6 days of continuous operation), and relatively high x-ray sensitivity (20.7 μC Gy⁻¹cm⁻² for the Fe-doped device). Furthermore, the reduced oxygen vacancy concentration can improve the photocurrent/dark current ratio of the detector. This study proposes an innovative approach for high-performance x-ray detectors based on β-Ga₂O₃ single crystals.

Conclusion

      To sum up, two types of β-Ga₂O₃ single crystal wafers were introduced for fabricating x-ray detectors. The fundamental properties and device performance were systematically compared. It was found that Fe can effectively compensate free electrons, significantly enhance the resistivity of the single crystals, and enable the fabrication of high-performance x-ray detectors. The Fe-doped β-Ga₂O₃-based detectors demonstrate superior x-ray performance in ambient air at room temperature, including a high photo-to-dark current ratio, low noise density, and excellent operational stability. These results indicate the significant potential of Fe-doped β-Ga₂O₃ single crystals for x-ray detection applications.