Recently, the scientific research team of the Institute of Metallurgy, Chinese Academy of Sciences invented a new type of photodetector -light-controlled diode. It has a new signal behavior, that is, under light, the device can change from a non-conductive "fully off state" to a light-only It has a "rectifying state" that conducts electricity in the voltage direction.
Picture | From right: Researcher Sun Dongming, Associate Researcher Sun Yun, Dr. Feng Shun, Researcher Liu Chi, doctoral student Han Ruyue, doctoral student Li Bo (Source: Data map)
Using this as the basic unit, the team prepared for the first time An anti-crosstalk optoelectronic memory array that does not require the use of gating devices provides a basic device for the ultimate realization of highly integrated optoelectronic arrays in the future, and can be used in new optoelectronic logic circuits. It is a new circuit component and a previously "missing component" that can pave the way for highly integrated, low-power smart optoelectronic systems.
Specifically, light-controlled diodes are expected to play an irreplaceable key role in optical logic, information processing, high-precision imaging and other optoelectronic systems. For example, using light signals as basic input parameters can control the basic logical functions of optoelectronic devices , greatly improving the light control efficiency of the devices and fundamentally subverting the existing photoelectric conversion architecture and basic logical understanding.
(Source: National Science Review)
This kind of optical logic operation from the fully off state to the rectification state has the single-directional conduction function of the rectification state under lighting conditions, so it can avoid array crosstalk under the condition of no gate. question. Using light-controlled diodes as the basic unit and integrated into the image sensor, helps to shrink the size of the array pixel unit and further improve the array integration, while reducing the power consumption and complexity of the device.
Recently, a related paper titled "A photon-controlled diode with a new signal-processing behavior" [1] was published on National Science Review (23.18). Researchers Liu Chi, Cheng Huiming, and Sun Dongming of the Institute of Metal Research, Chinese Academy of Sciences serve as co-corresponding authors.
Figure | Related papers (Source: National Science Review)
All three reviewers believe that this device has a new and interesting signal processing characteristic and is an important progress in the field of photodetectors. For example, reviewer 1 commented: “The author has fabricated a new type of light-controlled diode that can change from the off state to the rectifying state, thereby forming an optoelectronic storage array without gating devices and crosstalk. "Significant progress has been made in the field."
Reviewer 2 emphasized: "Due to this new signal processing behavior, light-controlled diode arrays without any pass devices will not show crosstalk, which is very important for future highly integrated, low-power systems. Very important. I think this device with new properties is very interesting, it is an expanded family of optoelectronic devices that has never been achieved before."
The field of photodetectors has ushered in important progress over the past 70 years, transistors and Integrated circuit technology has achieved amazing development results along the lines of Moore's Law and . As the characteristic sizes of components approach the process and physical limits, on the one hand, integrated circuits will develop along the technical route of scaling down and three-dimensional integration; on the other hand, new forces in the future development of integrated circuits include sensory memory computing brain-like chips, Optoelectronic chips and quantum chip and other technologies.
As an important type of device, photodetectors are semiconductor devices that detect light signals through electrical processes. Typical photodetectors include photodiodes , phototransistors, photoconductors , etc. Although there are many types of photodetectors, their principles and architectures vary.However, depending on the different performances of the device output electrical parameters under photoresponse conditions, the representative device working behavior is manifested in a limited number of aspects.
(Source: National Science Review)
Before and after being excited by a light signal, the change in the output current-voltage relationship of the photodetector has three typical states: fully closed state, fully open state and rectified state. For example, when a typical device represented by a photodiode is exposed to light, the output signal changes from a rectified state to a fully-on state. On the other hand, the output signal of a class of devices represented by photoconductors and phototransistors changes from a fully off state to a fully on state.
Judging from the completeness of the signal change type, there may be a type of device that changes the output signal from a fully off state to a rectified state. The realization of this new type of photodetector device is expected to play a key role in optoelectronic systems such as optical logic, information processing, and high-precision imaging. For example, if uses it as a basic pixel unit, it can build an anti-crosstalk photoelectric array without a gate.
Because every possible leakage path in the array is cut off by its rectification effect, it itself acts as a switch, so there is no need for another gating device, which can greatly save circuit area and complexity. , laying the foundation for the ultimate realization of highly integrated arrays.
(Source: National Science Review)
In order to realize this new device, the team selected two-dimensional material with excellent optoelectronic properties as the device material, and at the same time constructed the heterojunction device together with the bulk material. Specifically, it inserts a MoS2 n/n− junction between two graphene/MoS2 Schottky junctions to form a channel, uses BN material as a grating layer, and controls the Schottky junction by capturing and releasing photogenerated carriers. On and off, thereby revealing or inhibiting the rectification characteristics of the MoS2 n/n− junction, thereby realizing for the first time a new signal behavior in which the device current state converts from a fully off state to a rectification state under light.
Constructing a 3×3 optoelectronic memory array without gating devices
Before the research on light-controlled diodes was carried out, the research group had already carried out a series of research work in the field of optoelectronics, including carbon nanotube photoelectric memory [2], carbon nanotubes neuromorphic photosensor array [3], double heterojunction phototransistor [4] and wafer-level MXene photodetection array [5], etc.
They found that in order to avoid crosstalk, when optoelectronic devices are integrated in the array, additional gating devices must be added to the array unit to control leakage current, which inherently limits the integration of the system. Liu Chi said: "We can't help but think, is it possible to develop an optoelectronic device that can achieve a crosstalk-free array without using a gating device?"
After conducting literature research, the team believed that if this function could be realized , a new type of optoelectronic device must be developed, which can convert between the two states of "full off" and "rectification" under light. Based on this, the research team began the design and construction of the device.
(Source: National Science Review)
The main research idea is to connect two Schottky junctions and a rectifier junction (diode) in series, and control the cutoff or conduction of the Schottky junction through the grating layer to suppress or reveal The rectifying function of the diode enables the device to switch from the "fully off state" to the "rectifying state".
Specific to material selection, combined with the team’s previous research experience, two-dimensional layered materials are used as the main part of the device, with graphene as the electrode material, molybdenum disulfide n/n− junction as the channel material, Hexagonal boron nitride is used as the grating layer.In the
research, they prepared van der Waals heterojunctions through dry transfer, and then used device processes such as oxygen plasma treatment, electron beam exposure, reactive ion etching, and electron beam evaporation to realize the construction of light-controlled diodes.
(Source: National Science Review)
After the construction of a single device, electrical and optoelectronic characterization was performed. Under a certain gate voltage, the device behaves in a fully off state in the dark, but can be converted into a rectified state when illuminated, and has a rectification ratio of more than 106, which is a great encouragement to the research team.
The team then experimented with the effect of different thicknesses of grating layers on device performance. When ultrathin hexagonal boron nitride (1nm) is used as the grating layer, the device can be used as a photodetector; as the thickness of the grating layer increases to more than 5nm, the photocurrent of the device exhibits non-volatile properties and can be used in photovoltaics. memory.
Further, they tested the device's response to light of different wavelengths and intensities. Since the grating mainly relies on the defect energy level in hexagonal boron nitride, the shorter the wavelength of the incident light, the more likely it is to excite deep defects. The photoelectricity of the device The more responsive it is.
Finally, the team used light-controlled diodes as the basic unit to construct a 3×3 optoelectronic storage array without gating devices, verifying the array's anti-crosstalk capability. At the same time, based on the differences in the device's response to light of different wavelengths and intensities, the wavelength selection and power selection functions of the array were also demonstrated.
Based on this work, the team plans to develop a spherical brain-like two-dimensional material circuit for artificial vision systems. By cooperating with relevant domestic scientific research units, wafer-level two-dimensional materials are used to build highly integrated, flexible, and transparent light-controlled diode arrays, and realize artificial vision system functions such as image detection, image memory, and image learning.
Going forward, they plan to develop a curved light-controlled diode array. At that time, the evolution of the performance of spherical light-controlled diodes and the relationship between spherical arrays and detection angles will be studied, and the functional verification of combining with artificial carriers such as contact lenses will be explored.
-End-
Reference: 1, Shun Feng, Ruyue Han, Lili Zhang, Chi Liu, Bo Li, Honglei Zhu, Qianbing Zhu, Wei Chen, Hui-Ming Cheng, Dong-Ming Sun, A photon-controlled diode with a new signal-processing behavior, National Science Review, 2022;, nwac088, https://doi.org/10.1093/nsr/nwac0882, Advanced Materials, 32, 1907288, 2020 3、Nature Communications, 12, 1798, 20214、Nature Communications, 12, 4094, 20215, Advanced Materials, 2201298, 2022
