Reviewed by Lexie CornerMar 12 2025
A team of researchers from the Shanghai Institute of Technical Physics, led by Professor Weida Hu, has developed a new optoelectronic memory device using black phosphorus on indium selenium. This device utilizes band-to-band tunneling (BTBT) to achieve high-speed, low-voltage operation and near-infrared sensitivity.
Working principle of the critical BTBT memory. a. Schematic diagram of the critical BTBT memory. b Negative photomemory characteristics of the critical BTBT memory in response to multiple 520 nm laser pulses with a duration of 500 ns. c Band alignments are depicted at Vg < 0 with a constant Vd. Only when the critical BTBT condition is satisfied does the device exhibit negative and non-volatile photo memory characteristics. Image Credit: Hangyu Xu, Runzhang Xie, et al.
Traditional processing system designs typically separate sensory units from memory and computation components. High-power analog-to-digital conversion (ADC) is used to transfer visual data to binary memory, where it is processed by computational units. This separation leads to speed discrepancies and power consumption issues due to high data transfer overhead.
Optoelectronic memory has potential for combining memory and sensing while minimizing data transfer, but it still faces limitations. Photogating and Fowler-Nordheim tunneling-based technologies are constrained by high barriers and unclear trap energy levels, which result in slow response times and high operating voltages.
The critical BTBT memory device operates at low voltage and with a cumulative photomemory current, meeting the critical BTBT condition through precise band alignment. The device operates in the near-infrared range (940 nm) due to its small barrier.
Additionally, optoelectronic memory devices can store motion, which is represented as the streaming of images across successive frames. The movement trajectory is uniquely defined when combined with an interframe algorithm.
The critical BTBT memory's optoelectronic performance improves neuromorphic vision hardware, allowing accurate moving target tracking and recognition without motion blur.
To better understand the underlying mechanism, the researchers conducted comparative experiments using identical device structures with different materials. They found that the device only exhibits negative and non-volatile current under optical stimulation when the band alignment meets the critical BTBT condition.
They also identified two distinct negative differential resistance (NDR) points, providing clear evidence of electron tunneling and hole memory. The discovery of a novel tunneling mechanism can potentially improve efficiency and performance, representing a significant advancement in ultrafast, high-bandwidth, intelligent optoelectronic memory.
The researchers summarized the critical BTBT memory's working principle in light of their findings.
Researchers said, “The anomalous optoelectronic memory characteristics are attributed to two main factors: (1) The photo-generated carriers are rapidly separated via critical BTBT; (2) The spatial overlap between the electron tunneling region and the hole storage region is minimized, leading to a low recombination rate. We have done a lot of experiments and simulations and found that this photoelectric storage phenomenon does not occur if either of these principles is violated.”
“The discovery of dual NDR points is strong evidence supporting our assumption. Thanks to the critical BTBT, our device demonstrates record photo-memory speed across a wide wavelength range,” the authors added.
“The presented technique can be used for moving target tracking and recognition, enhancing system efficiency. By reducing exposure time, it becomes particularly effective for fast-moving target scenarios, minimizing motion blur and significantly improving accuracy. This innovation could lay the foundation for the development of advanced neuromorphic vision hardware, with the potential to transform human life by enabling smarter, more responsive systems in various applications.”
Journal Reference:
Xu, H., et al. (2025) Critical band-to-band-tunnelling based optoelectronic memory. Light: Science & Applications. doi.org/10.1038/s41377-025-01756-7.