【Domestic Papers】Thermal tuning of the bandgap in β-(AlₓGa₁₋ₓ)₂O₃/Al₂O₃ heterostructures for tunable photodetector performance

      Researchers from the Fuzhou University have published a dissertation titled "Thermal tuning of the bandgap in β-(Al_xGa_1-x)₂O₃/Al₂O₃ heterostructures for tunable photodetector performance" in Optical Materials.

Background

      β-gallium oxide (Ga₂O₃), due to its wide bandgap, low cost, and excellent chemical and thermal stability, has emerged as a key material in the field of fourth-generation semiconductors, driving significant applications such as solar-blind photodetectors high-temperature gas sensors, photoluminescent devices electroluminescent devices, power devices, and resistive switching memory devices. The optical bandgap of β-Ga₂O₃ is approximately 4.9 eV, corresponding to a wavelength of ∼253 nm in the UV range. However, UV photodetectors are typically employed within the wavelength range of 200–300 nm. Consequently, an effective strategy is urgently required to modulate the bandgap of β-Ga₂O₃, making it suitable for a broader range of ultraviolet detection wavelengths.

Abstract

      The ultrawide-bandgap semiconductor Ga₂O₃, characterized by its high breakdown voltage, demonstrates significant potential for applications in optoelectronics and photonics. In this study, we propose a cost-effective strategy for the scalable production of Al-doped Ga₂O₃ via post-growth thermal annealing. Our results demonstrate that the binary β-Ga₂O₃ films are first alloyed into ternary (-201) β-(Al_xGa_1-x)₂O₃ alloys with tunable compositions under optimized annealing conditions, ultimately forming β-(Al_xGa_1-x)₂O₃/Al₂O₃ heterostructures. Specifically, through X-ray diffraction (XRD) analysis, the Al content of the β-Ga₂O₃ template samples without annealing and annealed up to 1300 °C ranges from 0 to 0.598, with the optical bandgap tunable from 5.01 eV to 6.30 eV. Moreover, the resulting ultraviolet photodetectors based on these composites exhibit enhanced photoresponse performance, with a low dark current of 16.6 fA, a maximum on/off current ratio of 4.53 × 10⁶, and a remarkable responsivity of 5.48 A/W. This study provides a straightforward and efficient approach for tailoring the bandgap of β-(Al_xGa_1-x)₂O₃ films for deep-ultraviolet optoelectronic applications.

Highlights

      Cost-effective, scalable fabrication of (-201)-oriented β-(Al_xGa_1−x)₂O₃/Al₂O₃ heterostructures.

      Al content increases from 0 to 0.598 upon annealing, while the bandgap is tunable from 5.01 to 6.30 eV.

      UV photodetectors exhibit a dark current of 16.6 fA, an on/off ratio of 4.53 × 10⁶, and a responsivity of 5.48 A/W.

Conclusions

      In sum, this work proposes a low-cost and scalable method for producing wafer-scale β-(Al_xGa_1-x)₂O₃/Al₂O₃ heterostructures via a controllable high-temperature treatment process. XRD analysis reveals that both the as-grown and annealed films are highly oriented along the (-201) plane, with a notable shift of diffraction peaks to higher angles due to Al–Ga interdiffusion. Thermal treatment results in an increase in film thickness from 195 nm to 483 nm and a corresponding widening of the optical bandgap from 5.01 eV to 6.30 eV. Furthermore, ultraviolet photodetectors fabricated from these alloys exhibit excellent optoelectronic performance, featuring an ultralow dark current of 16.6 fA, a peak on/off current ratio of 4.53 × 10⁶, and a high responsivity of 5.48 A/W. These results demonstrate that a simple and efficient thermal interdiffusion process enables bandgap tuning in β-(Al_xGa_1−x)₂O₃ films, thereby yielding materials capable of responding to shorter deep-ultraviolet wavelengths and further enhancing their application potential in deep-UV optoelectronics.