Multiframe-integrated, in-sensor computing using persistent photoconductivity

The utilization of processing capabilities within the detector holds significant promise in addressing energy consumption and latency challenges. Especially in the context of dynamic motion recognition tasks, where substantial data transfers are necessitated by the generation of extensive information and the need for frame-by-frame analysis. Herein, we present a novel approach for dynamic motion recognition, leveraging a spatial-temporal in-sensor computing system rooted in multiframe integration by employing photodetector. Our approach introduced a retinomorphic MoS_(2) photodetector device for motion detection and analysis. The device enables the generation of informative final states, nonlinearly embedding both past and present frames. Subsequent multiply-accumulate (MAC) calculations are efficiently performed as the classifier. When evaluating our devices for target detection and direction classification, we achieved an impressive recognition accuracy of 93.5%. By eliminating the need for frame-by-frame analysis, our system not only achieves high precision but also facilitates energy-efficient in-sensor computing.

Suppression of persistent photoconductivity in high gain Ga_(2)O_(3) Schottky photodetectors

The defect-related photoconductivity gain and persistent photoconductivity(PPC)observed in Ga_(2)O_(3)Schottky photodetectors lead to a contradiction between high responsivity and fast recovery speed.In this work,a metal-semiconductor-metal(MSM)Schottky photodetector,a unidirectional Schottky photodetector,and a photoconductor were constructed on Ga_(2)O_(3)films.The MSM Schottky devices have high gain(>13)and high responsivity(>2.5 A/W)at 230-250 nm,as well as slow recovery speed caused by PPC.Interestingly,applying a positive pulse voltage to the reverse-biased Ga_(2)O_(3)/Au Schottky junction can effectively suppress the PPC in the photodetector,while maintaining high gain.The mechanisms of gain and PPC do not strictly follow the interface trap trapping holes or the self-trapped holes models,which is attributed to the correlation with ionized oxygen vacancies in the Schottky junction.The positive pulse voltage modulates the width of the Schottky junction to help quickly neutralize electrons and ionized oxygen vacancies.The realization of suppression PPC functions and the establishment of physical models will facilitate the realization of high responsivity and fast response Schottky devices.

Self-magnetism and Persistent Photoconductivity

Persistent photoconductivity has been investigated by various models, among which the Macroscopic Barrier model, Large-Lattice-Relaxation model, and Random Local Potential Fluctuations model are mostly well known. Although the three well-known models have played important roles in describing the persistent photoconductivity, they are not the principal cause of persistent photoconductivity. In this paper a classical model originated from ＂selfmagnetism of electron gas＂ is proposed to illustrate the persistent photoconductivity phenomenon. This classical model is based on electron gas pulsation, which depends on the charge density. Different concentrations of current carriers create different frequencies in the system, and thus the system is sensitive to different wave lengths of incident light. Then the construction of different detectors can be possible for different wave lengths of incident light.

Ultraviolet irradiation dosimeter based on persistent photoconductivity effect of ZnO

It is essential to determine the accumulative ultraviolet(UV)irradiation over a period of time in some cases,such as monitoring UV irradiation to the skin,solar disinfection of water,photoresist exposure,etc.UV colorimetric dosimeters,which use dyes'color change to monitor the amount of UV exposure,have been widely studied.However,the exposure data of these UV colorimetric dosimeters can hardly be converted to digital signals,limiting their applications.In this paper,a UV dosimeter has been proposed and demonstrated based on the persistent photoconductivity(PPC)in zinc oxide microwires(ZnO MWs).The PPC effect usually results in high photoconductivity gain but low response speed,which has been regarded as a disadvantage for photodetectors.However,in this work,the unique characteristics of the PPC effect have been utilized to monitoring the accumulative exposure.We demonstrate that the photocurrent in the ZnO MWs depends on the accumulative UV exposure due to the PPC effect,thus the photocurrent can be utilized to determine the UV accumulation.The dosimeter is immune to visible light and exhibits a photoconductive gain of 2654,and the relative error of the dosimeter is about 10%.This UV dosimeter with electrical output is reusable and convenient to integrate with other electronic devices and may also open a new application area for the PPC effect.

Origin of the giant persistent photoconductivity in LaAlO_(3)/SrTiO_(3)heterostructures probed by noise spectroscopy

LaAlO_(3)/SrTiO_(3)(LAO/STO)heterostructures have shown a strong persistent photoconductivity(PPC)at room temperature.The abnormally strong PPC has attracted immense research interest due to its possible applications in optically-tunable electronic devices.Despite its promise,the fundamental understanding of the PPC in the LAO/STO heterostructures is still elusive.Herein,we report that the giant PPC origi-nates from the photo-induced valence change in oxygen vacancies near the LAO/STO interface.Our spec-tral analysis of the photocurrent and the model-fitting study consistently show that the ionized oxygen vacancies near the interface are neutralized during the electron relaxation process.They hinder the complete relaxation of the photoexcited electrons by the deeply-located oxygen vacancies and result in the strong PPC.The change in the ionization state distribution of the oxygen vacancies is probed by the per-sistent noise behavior at the frequency between 1 kHz and 20 kHz regime.These results provide insight into the role of oxygen vacancies in influencing the internal charge distribution and triggering the PPC phenomena in complex oxide heterostructures.

Persistent photoconductivity in neutron irradiated GaN

Unintentionally doped GaN films grown by MOCVD were irradiated with neutrons at room temperature. In order to investigate the influence of neutron irradiation on the optical properties of GaN films, persistent pho toconductivity （PPC） and low temperature photoluminescence （PL） measurements were carried out. Pronounced PPC was observed in the samples before and after neutron irradiation without the appearance of a yellow lumi- nescence （YL） band in the PL spectrum, suggesting that the origin of PPC and YL are not related. Moreover, PPC phenomenon was enhanced by neutron irradiation and quenched by the followed annealing process at 900 ℃. The possible origin of PPC is discussed.

A systematic study of light dependency of persistentphotoconductivity in a-InGaZnO thin-film transistors

Persistent photoconductivity(PPC)effect and its light-intensity dependence of both enhancement and depletion(E-/D-)mode amorphous InGaZnO(a-IGZO)thin-film transistors(TFTs)are systematically investigated.Density of oxygen vacancy(V O)defects of E-mode TFTs is relatively small,in which formation of the photo-induced metastable defects is thermally activated,and the activation energy(E a)decreases continuously with increasing light-intensity.Density of V O defects of D-mode TFTs is much larger,in which the formation of photo-induced metastable defects is found to be spontaneous instead of thermally activated.Furthermore,for the first time it is found that a threshold dose of light-exposure is required to form fully developed photo-induced metastable defects.Under low light-exposure below the threshold,only a low PPC barrier is formed and the PPC recovery is fast.With increasing the light-exposure to the threshold,the lattice relaxation of metal cations adjacent to the doubly ionized oxygen vacancies(V O^2+)is fully developed,and the PPC barrier increases to∼0.25 eV,which remains basically unchanged under higher light-exposure.Based on the density of V O defects in the channel and the condition of light illumination,a unified model of formation of photo-induced metastable defects in a-IGZO TFTs is proposed to explain the experimental observations.

Persistent photoconductivity of amorphous Hg0.78Cd0.22Te：In films

The persistent photoconductivity（PPC） of amorphous Hg（0.78）Cd（0.22）Te. In films has been studied under illumination by super-bandgap light（a He–Ne laser, hv=1.96 eV, 30 mW/cm^2） and sub-bandgap light（1000 K Blackbody source, the largest photon energies h vp=0.42 eV, 8.9 mW/cm^2） in the range of 80–300 K. The persistent photoconductivity effect increases with increase in illumination intensity and illumination time. However,it decreases with increase in working temperature. The non-exponential decay of photoconductivity implies the presence of continuous distribution of defect states in amorphous Hg（0.78）Cd（0.22）Te. In films. These results indicate that the decay of photoconductivity is not governed by the carrier trapped in the intrinsic defects, but it may be due to light-induced defects under light illumination.

Interface terminal group regulated organic phototransistors with tunable persistent and switchable photoconductivity

With both light detection and intrinsic amplification functions,organic phototransistors have demonstrated promising applications,including photodetection and photomemory.To achieve excellent photoresponse and superior photogain,a common and effective strategy is to modulate the trapping effect with the purpose of reducing recombination or prolonging the lifetime of the photogenerated charge carriers.However,introducing trapping sites delicately is challenging and might sacrifice the response rate together with a typical persistent photoconductivity.Here,we demonstrate a facile strategy for achieving high photo-responsive organic phototransistors with both persistent and switchable photoconductivity features via interface terminal group regulation.By varying the terminate groups of self-assembled monolayer(SAMs)from the strong electron withdrawing group-F,neutral−CH_(3) to electron donating−NH_(2) on the dielectric surface,we realize both minority carrier trapping and majority carrier trapping in the organic phototransistor based on the C8-BTBT active layer.The electron withdrawing effect of F significantly enhances the minority carrier trapping process and yields a high photoresponsivity with a long-lasting persistent photoconductivity.In contrast,the electron donating group−NH_(2) with a distinct majority carrier trapping ability causes switchable photoconductivity so that the photocurrent can rise pronouncedly and fully decay along with light on/off.Attractively,both cases can deliver high performance with photoresponsivities higher than 104 A W^(−1) together with a photosensitivity in the level of 107 and a detectivity of approximately 10^(15)–10^(16) Jones.Such a tunable,excellent photoresponse property enables the convenient exploration of organic phototransistors to satisfy different application requirements.

A method for modeling and deciphering the persistent photoconductance and long-term charge storage of ZnO nanorod arrays

The controllability of persistent photoconductance （PPC） and charge/energy storage of ZnO nanorod arrays （NRAs） were demonstrated experimentally by tuning the nanorod diameter. The dependency of the ZnO NRAs＇ photoelectric characteristics on the nanorod diameter suggests that the Debye length and photon penetration depth in ZnO could spatially partition a standalone nanorod into three different photoelectric functional regions （PFRs）. Theoretically, a series of rate functions was employed to describe the different extrinsic/intrinsic carrier photogeneration/recombination dynamic sub-processes occurring in the different PFRs, associated with oxygen chemisorption/photodesorption, oxygen vacancy photoionization, and electron trapping by photoionized oxygen vacancies. On the basis of the coupled contributions of these different dynamic sub-processes in the photoelectric properties of the ZnO NRAs, a thorough-process photoelectric dynamic model （TPDM） was proposed using the simultaneous rate functions. Through solving the rate functions, the corresponding analytical equations could be employed to simulate the time-resolved PPC spectra of the ZnO NRAs, and then the quantitative parameters extracted to decipher the PPC and charge/energy storage mechanisms in the ZnO NRAs. In this way, the TPDM model provided a numerical-analytical method to quantitatively evaluate the photoelectric properties of ZnO NRA-based devices. Additionally, the TPDM model revealed how the different photoinduced carrier dynamics in the different PFRs could play functional roles in different optoelectronic applications, e.g., photodetectors, photocatalysts, solar cells and optical nonvolatile memories, and thus it illuminated a practical approach for the design of ZnO NRA-based devices via optimization of the modularized spatial configuration of the PFRs.