【Domestic Papers】Transition-Rule Defined Polarization Detection of β-Ga₂O₃ for Wavelength-Dependent Sensing of Amino Acid

      Researchers from Songshan Lake Materials Laboratory and Shandong University of Technology have published a paper titled "Transition-Rule Defined Polarization Detection of β-Ga₂O₃ for Wavelength-Dependent Sensing of Amino Acid" in Laser & Photonics Reviews.

Project Support

      This work was supported by the National Natural Science Foundation of China (Grant Nos. 12174275, 62174113, 12204471, and 12474073) and the Youth Innovation Team of Colleges and Universities in Shandong Province (Grant No. 2022KJ223).

Background

      Polarization photodetectors (PPDs) have extensive applications in medical imaging, optical communication stress imaging and defogging imaging since the polarization state carries the information of surface roughness, texture pattern, and physical and chemical properties which are unattainable in conventional intensity-based PDs. Furthermore, the integration of PPDs with light-triggered color-switching materials and humidity-responsive spin-state materials could enable multi-modal optical sensing systems for secure communication and adaptive environmental monitoring. Integration with wire grids has achieved great success in visible infrared and Terahertz bands, where polarization cameras are now commercially available globally. However, the development of wire-grid deep-ultraviolet (DUV) PPDs is encountering tremendous obstacles due to the difficulties in preparing high-density nanoscale wire grids on a large scale. It is well known that the wire-grid period must be less than the incident wavelength to ensure a high extinction ratio according to the effective medium theory. β-Ga₂O₃ has received significant research attention due to its ultrawide bandgap, high photoresponsivity (R), and anisotropic optical properties in this special band. Compared to integrating metal-grid structure with periods of 100 and 167 nm using a sophisticated focused ion beam process, utilization of the low-symmetric nature of β-Ga₂O₃ would be more appealing for the advance of DUV PPDs.

Abstract

      Selective electron transitions are critical for polarization detection due to the high sensitivity of optoelectronic conversion to symmetry properties. This work proposes a transition-rule-defined wavelength-dependent polarization detector using low-symmetry β-Ga₂O₃. Density functional theory calculation is applied to predict the dependence of photoresponse bands on polarization angles. A combination of angle-resolved polarization Raman spectroscopy and polarized transmittance spectra is utilized to corroborate the anisotropic optical properties of β-Ga₂O₃. Intriguingly, a notable proportional inversion of the polarization ratio (PR) emerges at 245 nm when altering the detection wavelength of the β-Ga₂O₃ photodetector (PD). Specifically, the photoresponse contrast between E//b and E//c directions, termed responsivity PR, can be boosted from 75 at 254 to 462 at 263 nm, while the minimum reaches 1/388 at 231 nm. The unique phenomenon of wavelength-dependent polarization detection in β-Ga₂O₃ PD well coincides with the density functional theory calculations concerning the selective transition of photoelectrons from split valence bands to the conduction band minimum. Finally, the new transition-rule-defined deep-ultraviolet polarization detector is leveraged to discriminate amino acids. This work demonstrates the remarkable meaning of a delicate control of the selective electron transitions in β-Ga₂O₃ polarization PDs for amino acid sensing with high sensitivity and specificity.