A photodetector with history-dependent dynamical responses to optical inputs could offer an essential breakthrough in performing temporal vision processing and time-series prediction without the requirement for sophisticated circuitry and undesired high energy consumption. Till now, memristor dynamics and its effective modulation with photo illumination have been utilized to mimic bio-inspired vision processing. Despite significant effort, it is still challenging to process real-time analogue temporal optical information with high accuracy, which requires developing a photonic counterpart of the electric-triggered memristor. Here, we report on the development of a Ga2O3-based proof-of-concept memphotoristor, in which memristive dynamics were stimulated with ultraviolet photon flux rather than conventional voltage. Specifically, a distinct hysteresis loop opening appeared in the cyclic photocurrent-ultraviolet intensity curves, where the magnitude of the loop opening depends on the photon flux. Additionally, light-illumination-induced fading memory, nonlinearity, and temporal dynamics were successfully utilized to demonstrate in-sensor reservoir computation and time-series prediction with an accuracy of 98.86%. Our research will pave the way to developing a wide range of cutting-edge optoelectronics for various applications, such as photosensors, photonic memory storage, and neuromorphic vision sensing of objects in real time.
This study was supported through the National Research Foundation of Korea [ NRF- 2023R1A2C2003242 , NRF–2019R1A2C2003804 and NRF-2022M3I7A3037878 ] of the Ministry of Science and ICT , Republic of Korea.Since the key to realizing the RC with a photodetector is to have a significant number of in-gap states (i.e., defects), initially we studied the growth of Ga2O3 [33]. Indeed, not only does Ga2O3 have a broad band gap (Eg ∼ 4.4–4.9 eV), but it also has rich in-gap states, which enable it to be utilized as one of the materials in the design of a memphotoristor. The cross-section transmission electron microscopy (TEM) image of the Ga2O3 thin film (thickness ∼ 60 nm) grown on p++-Si (resistivity ∼10−3 Ω-cm) is shown in Fig. 1c, showing a uniform and smooth interface with top Au/Cr and bottom native oxide (SiO2, ∼2 nm) covered Si. Additionally, the magnified TEM image from the Ga2O3 is shown in Fig. 1d, which confirms that the film is mostly amorphous, indicating that in-gap states could be the predominant [30]. For clarity, the Gaussian-fitted arrangements of the atoms from the magnified TEM image are shown in the inset of Fig. 1d, making it clear that the film contains defects [30, 33–35]. Further, the elemental distribution was mapped using the electron energy loss spectroscopy (EELS) measurements, which reveal that the Ga and O have the atomic percentages of 38 and 56%, respectively, and are uniformly distributed across the film (Fig. 1e), leading to the formation of Ga2O3, which is supported by energy-dispersive spectroscopy (EDS) measurements (see Fig. S1, Supporting Information). For the oxidation state analysis, EELS spectra were collected from bottom Si to Au–Cr (see dotted white line in Fig. 1e), which show an oxygen K-edge with two main peaks, labelled A (∼535.6 eV) and B (∼539.8 eV) that are related to the O 2p-Ga 4s and O 2p-Ga 4p bonding, respectively, as shown in Fig. 1f.This study was supported through the National Research Foundation of Korea [NRF- 2023R1A2C2003242, NRF–2019R1A2C2003804 and NRF-2022M3I7A3037878] of the Ministry of Science and ICT, Republic of Korea.
