【Member Papers】Professor Tang Weihua's research team at Nanjing University of Posts and Telecommunications —— Self-powered solar-blind detector array based on ε-Ga₂O₃ Schottky photodiodes for dual-mode binary UV communication

      Wide bandgap semiconductor Ga₂O₃ with a bandgap of around 4.9 eV is a preferred choice to perform solar-blind photodetection, which has lots of applications in both military and civilian fields. The study on Ga₂O₃ materials and devices has been reported by many research institutions around the world, while the photodetector array of high performances and optical integration remains huge challenges. Metal-semiconductor-metal Ga₂O₃ photodetector array verified its prospect for applications, while the large dark current and low signal-to-noise ratio led to low resolution and contrast. This project intends to construct Schottky photodiode array, and solar-blind UV communication based on optical integration. The Schottky barrier at the metal-semiconductor interface could quickly separate the photo generated carriers for improving the photo response, especially for the photo-to-dark current ratio and response speed, etc. that are key parameters for achieving fast and accurate optical communication.

      In this work, a solar-blind UV metal-semiconductor Schottky photodiode array is constructed by using metalorganic chemical vapor deposition grown ε-Ga₂O₃ thin film, possessing high-performance and self-powered characteristics, towards dual-mode (self-powered and biased modes) binary light communication. The 4×4 square layout in this work is more conducive to saving the occupied area of the detector array, conducive to integrated applications, and does not require complex insulation isolation technology. The current signal can be recorded and read out by an external circuit in a single and rapid manner. For the array unit, the responsivity, specific detectivity and external quantum efficiency are 30.8 A/W/6.3×10^-2A/W, 1.51×10⁴%/30.9%,1.28×10¹⁴/5.4×10¹² Jones for biased (-10 V)/self-powered operation. In particular, the rise and decay time are 0.19 ms and 7.96 ms at biased modes, respectively; suggesting an ability to trace fast light signal. In addition, the maximum standard deviation of the array photocurrent is only 4.3%, highlighting the importance of accurate information communication. Finally, the application of Ga₂O₃-based photodiode array for solar blind ultraviolet communication is presented. At self-powered and bias modes, the digital signal of the array unit is collected by defining the high current signal as digital signal 1 and the low current signal as digital signal 0, and then the two characters "NY" and "IC" are decoded through ASCII codes. Dual-mode binary deep ultraviolet communication is realized. In all, this work would provide useful references for the development of wide band gap Ga₂O₃-based optoelectronics.

      In summary, the preparation of high-performance Ga₂O₃ based Schottky barrier photodiode array detectors will provide useful guidance for the development of wide bandgap optoelectronics based on Ga₂O₃. In addition, compared to discrete devices, array devices can greatly reduce the time required for signal transmission and can also transmit clearer and more accurate information. This has opened up new directions for promoting the research of gallium oxide based materials in the field of ultraviolet communication applications.

(a) The schematic diagram of the ε-Ga₂O₃-based Schottky photodiode array, (b) and (c) are its partial enlarged figures. (d) The AFM image, (e) XRD pattern, and (f) UV-vis absorbance spectrum of the prepared ε-Ga₂O₃ thin film. (g) The spectral response of one array unit.

(a) The schematic photograph of the optical communication system based on ε-Ga₂O₃ Schottky photodiode array. The time response of the array unit illuminated for 1 s at (b) self-powered mode and (d) reverse biased mode, respectively. The optical communication results based on ASCII codes at (c) self-powered mode and (e) reverse biased mode, respectively.