【Domestic Papers】Combination of Gallium Oxide Power Devices and DUV Optoelectronic Devices (3)

07 High performance TiO2@GaOxNy-Ag heterojunction photodetector with plasma assisted enhancement

      Gallium Oxide (Ga₂O₃ ) materials provide a unique research perspective and broad application prospects in the field of photoelectric detection because of its ultra-wide optical band gap, high breakdown field strength, high Baliga’s figure of merit and excellent chemical and thermal stability. However, its intrinsic deep ultraviolet absorption edge and preparation method bring defects and impurities of the material itself, which affect the generation, separation and transfer of charge carriers in the photoelectric process, which makes the photoelectric detection performance is not ideal, and seriously hinders the practical application of its photoelectric devices.

      Recently, a team led by Professor Lu Hongliang and researcher Liu Wenjun at Fudan University reported the performance of TiO₂@GaO_xN_y-Ag ultraviolet-visible metal-semiconductor-metal (MSM) photodetector. The team realizes controlled N doping and interface correction of GaO₃ nanofilms based on atomic layer deposition, and combines the advantages of one-dimensional TiO₂₂ nanoarrays and the Ag surface plasmon resonance effect (SPR) to design a new heterojunction TiO@GaO_xN_y-Ag. Emphasis is placed on the structure-activity relationship between TiO₂@GaO_xN_y-Ag heterostructure and photoelectric detection performance. The results show that the response rate of TiO@GaON-₂Ag detector_x at_y 580 nm is 4 times that at 380 nm, and the detection rate and response time of TiO@GaON-Ag detector are better than those of single structure TiO and GaO detectors₂. ₂₃The excellent photoelectric detection performance of the heterojunction is mainly due to the synergistic effect of TiO₂@GaO_xN_y type II band structure and Ag particle SPR effect. This not only increases the absorption rate of light, but also promotes the effective separation of photogenerated carriers. At the same time, one-dimensional core-shell heterojunction nanowire arrays provide a large contact area for the photoelectric process, and also provide a direct path for photogenerated carrier transmission and separation. In addition, the experimental results have been strongly supported by FDTD simulation and calculation.

      The MSM detector based on TiO₂@Ga₂O_3xN_y-Ag heterojunction provides a unique path for the design of high-performance photoelectric conversion devices, and will facilitate the application of GaO based devices in the fields of sensing detection and imaging display.

      This paper is entitled “Surface plasmon assisted high-performance photodetectors based on hybrid TiO₂@GaO_xN_y-Agheterostructure” was published in the Journal of Semiconductors.

FIG. 1. TiO₂@GaO_xN_y-Ag device: (a) structure diagram, (b) optical display diagram; (c) I-V curves of Ga₂O₃ based devices with different structures. TiO₂@GaO_xN_y-Ag device at different wavelengths: (d) I-V curves, (e) I-T total curves, and I-T curves in a single period (f) 380 nm, (g) 480 nm, (h) 580 nm; (i) Comparison of optical responsivity of different devices.

FIG. 2. (a) TiO₂@GaO_xN_y-Ag structure used for FDTD simulation. (b) optical absorption simulation results of different devices. TiO₂@GaO_xN_y-Ag electric field simulation results under different wavelength illumination conditions: (c) 380 nm, (d) 480 nm, (e) 580 nm.

doi: 10.1088/1674-4926/44/7/072806

08 Based on PEDOT: Self-powered, self-healing sun-blind UV detector of PSS/Ga₂O₃ heterojunction

      In recent years, sun-blind UV detectors are expected to be applied in biological, medical and civil fields due to their weak background interference and low false warning rate. Wide-band gap semiconductor materials are considered as a popular choice for the preparation of sun-blind UV detectors. Gallium Oxide (Ga₂O₃) has a wide band gap (4.9eV), a large absorption coefficient, and a cutoff wavelength of about 250 nm. It is a promising solar blind UV detector material. The reported Ga₂O₃₃ based UV photodetectors are usually prepared on hard substrates and do not have mechanical flexibility, which greatly limits the application of GaO solar blind UV detectors in emerging electronic fields such as transparent, wearable and foldable. The self-healing device can recover automatically in the event of accidental damage, which can effectively extend the lifetime of the device. As a result, they have greater durability and lower replacement costs.

      Recently, the research group of Guo Daoyou, Distinguished professor at Zhejiang University of Science and Technology, built a self-powered, self-healing photodetector by constructing PEDOT: PSS/Ga₂O₃ heterojunction on a self-healing hydrogel substrate. The device uses an agarose/polyvinyl alcohol (PVA) double-network (DN) hydrogel substrate, which has reversible properties and enables hydrogen bonds to quickly re-form when broken hydrogels come into contact. In a period of about 30 seconds, the cut in the hydrogel can fully heal, allowing the photodetector to return to its original structure and function after damage. The photodetector light absorption layer is composed of a PEDOT: PSS/Ga₂O₃ heterostructure. Due to the Fermi energy level difference between PEDOT: PSS and Ga₂O₃₃, electrons flow from PEDOT: PSS to GaO until thermal equilibrium is reached. The formation of a depletion region at the interface of the two materials is able to effectively suppress the dark current, thus improving the detection capability of the device. When exposed to light, the photogenerated electrons in the Ga₂O₃ layer will flow to the silver nanowire (Ag NW) electrode under the action of the built-in electric field. At the same time, the photogenerated holes will be attracted and reach the electrode through the PEDOT: PSS layer. As a result, the photodetector showed a photoresponsiveness of 0.24 mA/W to sun-blind UV light at 254 nm, even without applied voltage.

      This paper presents a wearable solar-blind UV photodetector that can be used as an electronic skin application. The success gives the device self-power, excellent mechanical strength and excellent self-healing ability, which has great potential in the application of the next generation of smart devices.

      The article was published in the Journal of Semiconductors as "Self-Healing wearable self-powered deep ultraviolet photodetectors based on Ga₂O₃."

Figure 1. (a) Self-healing process of agarose/PVA hydrogels. (b) Self-healing mechanism of agarose/PVA hydrogels. (c) Freezing resistance of samples with or without addition LiCl hydrogel at -80℃. (d) LiCl improves the water-locking ability mechanism of agarose/PVA hydrogels.

Figure 2. (a) I-V curve of PEDOT: PSS/Ga₂O₃ photodetector. (b) I-V curve of the PEDOT: PSS/Ga₂O₃ photodetector under 0 V and 254 nm laser irradiation. (c) Photocurrent and responsivity of PEDOT: PSS/Ga₂O₃ photodetector under different light intensity densities. (d) Band map of PEDOT: PSS/ Ga₂O₃ heterojunction.

doi: 10.1088/1674-4926/44/7/072807

09 Optoelectronic synapses with amorphous Gallium Oxide homojunction are used for multifunctional signal processing

      In the era of big data, the optimization and updating of intelligent algorithms for accurate identification and information processing is evolving rapidly. However, the lag in the development of hardware devices has led to bottlenecks in increasing power consumption and speed during the processing of complex tasks. The main reason for this is the gradual failure of Moore's Law and the hindrance of the traditional von Neumann computing paradigm. At present, the perception-memory integrated computing strategy as an effective solution seems to be able to break the above barriers. The simulation of the basic unit of synapses, inspired by the human brain, offers possibilities for such solutions. At present, some excellent work is focused on the realization of artificial synapses regulated by electricity, light and other signals. However, both a single electrical signal and a single wavelength of light greatly limit the parallel processing capabilities of optoelectronic devices and future intelligent applications. Therefore, there is an urgent need to expand the types and operational range of tunable signals, thereby broadening the ability of synaptic devices to handle multiple types of tasks.

      Recently, Professor Shen Guozhen's research group at the Beijing Institute of Technology and Professor Li Yang's research group at Shandong University have proposed a multifunctional photoelectric synaptic (MFOS) device composed of Al/Ga₂O₃₃ (OR) /GaO (OD) /ITO. In this work, the main functional bilayer of the component device is sputtered from the same material under different experimental conditions, which undoubtedly greatly simplifies the complexity of device preparation. At the same time, a certain amount of defects are introduced into the double-layer film, and under the action of the energy band difference formed in the homojunction and the sustained photoconductivity effect, the electrical and optical signals can respectively induce MFOS to exhibit rich electrical and optical synaptic behavior. Further, in view of the good sensitivity of artificial synaptic devices to single wavelength (254 nm) optical signal frequency, two functions of high-pass filtering and small-scale visual array in photosynaptic mode have been successfully developed. Moreover, thanks to the difference in the light absorption range of the double-layer homogeneous material, MFOS allows simultaneous response to multiple wavelengths of signal. This modulation of multi-wavelength optical signals gives the synaptic device the ability of experiential learning, and the logic gate function after flipping the voltage reading has been successfully expanded.

      In summary, this work experimentally proves a multifunctional integrated optoelectronic synapse, which is expected to broaden the application scenarios of future artificial intelligence while improving the efficiency of future neuromorphic computing.

      The paper is entitled "Amorphous gallium oxide homojunction-based optoelectronic synapse for multi-functional signal processing "was published in the Journal of Semiconductors.

Figure 1. Device design and associated synaptic performance. (a) Schematic diagram of the MFOS device. (b) SEM image of cross-section. (c) Band diagram of carrier distribution of Ga₂O₃ (OD) and Ga₂O₃ (OR). (d) Schematic diagram of biological synapses transmitting neural signals. (e) Diagram of the result of continuous scanning curves under negative voltage and (f) positive voltage. (g) Schematic diagram of MFOS device under optical signal. Different optical synaptic response behavior of the device under optical signals of (h) 365 nm and (i) 254 nm.

doi: 10.1088/1674-4926/44/7/074101