【Domestic Papers】University of Science and Technology of China Has Made New Progress in the Field of High-energy Photon Detection

      Recently, Professor Long Shibing's Research Group at the School of Microelectronics of the University of Science and Technology of China has made new progress in Gallium Oxide high-energy photon detector. Aiming at the shortcomings of wide-bandgap semiconductor high-energy photon detectors in detection sensitivity and response speed, this research group first proposed a design strategy to improve detection performance by coupling interface pyroelectric effect and photoconductive effect based on PGR-GaO_X. This work fully embodies the application potential of the pyroelectric effect in the field of semiconductor photoelectric detection, providing a new reference for realizing highly sensitive and high-speed detectors. The relevant results were published in the internationally renowned journal Advanced Materials under the title “Pyroelectric Photoconductive Diode for Highly Sensitive and Fast DUV Detection”.

      High-energy photon detectors (for ultraviolet and X-ray bands) are very important in national security, biomedicine, industrial science and other fields. At present, commercial semiconductor materials such as Si, a-Se, etc. have problems with high leakage current and low X-ray absorption coefficient, which makes it difficult to meet the needs of high-performance detection technology. In contrast, wide-bandgap semiconductor Gallium Oxide materials show great potential in high-energy photon detection. However, due to the inevitable deep-level trap in the material aspect and the lack of effective design in the device structure, it has been difficult to realize the high sensitivity and high response speed broadband gap semiconductor high energy photon detector. The pyroelectric effect is introduced into the detector, which can help improve the comprehensive response characteristics of the detector by adjusting the separation, transmission and extraction of photogenerated carriers. The traditional pyroelectric effect exists in non-centrosymmetric materials. Recently, the discovery of the interfacial pyroelectric effect based on centrosymmetric materials provides a convenient path for the realization of high-performance detectors. However, the pyroelectric effect is weakened due to the joule heat generated when the detector operates at a higher bias voltage. Therefore, detectors based on this effect can only operate at low bias voltages, and the response current of the device is limited. To solve the above problems and meet the practical application requirements of high sensitivity and high-speed detectors, it is necessary to couple the pyroelectric effect with traditional photoconductivity or photovoltaic effect phase to make full use of its advantages.

      In response to the above challenges, Professor Long Shibing's research group designed a pyroelectric photoconductive diode based on PGR-GaOX, which achieved improved detection performance based on the coupling interface pyroelectric effect and photoconductive effect (FIG. 1a, b). This kind of pyroelectric photoconductive diode detector has extremely high sensitivity to deep ultraviolet and X-ray. Its response to UV is up to 10⁴A/W, and the sensitivity to X-ray is up to 10⁵μC × Gyair⁻¹/cm² (FIG. 1c, d). In addition, the interface pyroelectric effect caused by the polar symmetry of the depletion region of the PGR-GaOX device can significantly improve the response speed of the device by 10⁵ times, up to 0.1ms (FIG. 1e). Compared with the traditional photodiode (FIG. 1a, b), in the self-powered mode (@0V), due to the presence of the pyroelectric electric field, the pyroelectric photoconductive diode can generate greater gain at the instant of optical switching, in addition, the current polarity is opposite and the response speed is fast. The device principle is shown in FIG. 1f. In addition, the device can work in bias mode (photoconductivity mode), and the photocurrent gain is highly dependent on the bias, so ultra-high photocurrent gain can be obtained by increasing the bias voltage. When working in the photoconductive mode, the pyroelectric effect generated immediately after the light disappears accelerates the carrier recombination, prompting the device to achieve rapid recovery, thus improving the response speed of the device. The working principle of the device is shown in Figure 1g. Combined with the above characteristics, pyroelectric photoconductive diodes have great application potential in low-power and high-sensitivity imaging enhancement systems. This work not only shows that Ga₂O₃ is a promising high-energy photon detection material, but also provides a new scheme for the design of detectors with high sensitivity and high response speed.

FIG. 1. (a) Schematic diagram of PGR-GaOX-Based pyroelectric photoconductive diode structure. (b) Pyroelectric photoconductive diode and traditional photodiode in self-powered mode (I) and performance comparison in bias mode (II, III). (c) The dependence of the responsiveness and external quantum efficiency of the device on the light intensity under deep ultraviolet illumination. (d) The response current characteristic curve of the device under X-ray irradiation. (e) I-t response characteristic curve of the device under optical switching. At the moment of light off, 0 V electrical pulse operation can significantly improve the response speed of the device. (f) Optical response gain and current polarity change of the device under the optical switch in self-powered mode. (g) The photoconductance gain and the mechanism of the pyroelectric effect improve response speed under bias mode.

      Dr. Hou Xiaohu, School of Microelectronics, University of Science and Technology of China, is the first author of this thesis. Professor Long Shibing and Associate Researcher Zhao Xiaolong are the co-corresponding authors of this paper. The National Natural Science Foundation of China, the National Key R&D Program of China, the Basic Research Business Fund of Central Universities, and the China Postdoctoral Science Foundation supported the research. It was also supported by Anhui Provincial Key Laboratory of Integrated Circuit Science and Engineering, USTC Center for Micro- and Nanoscale Research and Fabrication, and Experimental Center of Information Science, University of Science and Technology of China.