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Review of photoresponsive properties at SrTiO <sub/>3</sub> -based heterointerfaces
摘要： The two-dimensional electron gas at SrTiO3-based heterointerfaces has received a great deal of attention in recent years owing to their potential for the exploration of emergent physics and the next generation of electronics. One of the most fascinating aspects in this system is that the light, as a powerful external perturbation, can modify its transport properties. Recent studies have reported that SrTiO3-based heterointerfaces exhibit the persistent photoconductivity and can be tuned by the surface and interface engineering. These researches not only reveal the intrinsic physical mechanisms in the photoresponsive process, but also highlight the ability to be used as a tool for novel all-oxide optical devices. This review mainly contraposes the studies of photoresponse at SrTiO3-based heterointerfaces.
关键词： persistent photoconductivity (PPC),complex oxides,two-dimensional electron gas,LaAlO3/SrTiO3 heterointerfaces
更新于2025-09-10 09:29:36
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Optimized preparation of Co-Pi decorated g-C3N4@ZnO shell-core nanorod array for its improved photoelectrochemical performance and stability
摘要： The cobalt-phosphate (Co-Pi) decorated g-C3N4@ZnO shell-core nanorod array (Co-Pi/g-C3N4@ZnO NRA) photoanode with broadened spectral response and optimized photoelectrochemical (PEC) performance was prepared. The g-C3N4@ZnO NRA was prepared via improved urea impregnation and calcination methods in semi enclosed environment. The g-C3N4 flexible slice shell was uniformly wrapped on ZnO nanorods core and the intimately contacted heterojunction was formed between the interface of g-C3N4 and ZnO. The g-C3N4@ZnO NRA promotes the separation and transfer of the photogenerated electron-hole pairs on g-C3N4 and ZnO under either visible light or white light illumination. The prepared g-C3N4@ZnO NRA was further electrodeposited with Co-Pi nanoparticles (NPs). The Co-Pi NPs can assist in the consumption of the photoinduced holes as well as pull the Fermi level potential of g-C3N4@ZnO NRAs towards the positive direction, resulting in the upward band bending at the band-edge position for Co-Pi/g-C3N4@ZnO NRAs and promoting the separation efficiency of the photogenerated electron-hole pairs. Consequently, the Co-Pi/g-C3N4@ZnO NRA exhibits an improved PEC performance under both visible light and white light illumination. In addition, g-C3N4 flexible slice shell decorated with Co-Pi NPs covered on the surface of ZnO NRAs core improved the stability of the ZnO NRA photoanode.
关键词： Heterojunctions,Photoconductivity and photovoltaics,Optical properties,Surfaces and interfaces,Semiconductors,Electrode materials
更新于2025-09-10 09:29:36
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Engineering Interface-Dependent Photoconductivity in Ge <sub/>2</sub> Sb <sub/>2</sub> Te <sub/>5</sub> Nanoscale Devices
摘要： Phase change materials are increasingly being explored for photonics applications, ranging from high resolution displays to artificial retinas. Surprisingly, our understanding of the underlying mechanism of light-matter interaction in these materials has been limited to photothermal crystallization, because of its relevance in applications such as re-writable optical discs. Here we report a photoconductivity study of nanoscale thin films of phase change materials. We identify strong photoconductive behaviour in phase change materials, which we show to be a complex interplay of three independent mechanisms: photoconductive, photo induced-crystallization and photo-induced-thermoelectric effects. We find these effects also congruously contribute to a substantial photovoltaic effect, even in notionally symmetric devices. Notably, we show that device engineering plays a decisive role in determining the dominant mechanism; the contribution of the photothermal effects to the extractable photocurrent can be reduced to < 0.4 % by varying the electrodes and device geometry. We then show that the contribution of these individual effects to the photoresponse is phase-dependent with the amorphous state being more photoactive than the crystalline state and that a reversible change occurs in the charge transport from thermionic to tunnelling during phase transformation. Finally we demonstrate photodetectors with an order of magnitude tuneability in photodetection responsivity and bandwidth using these materials. Our results provide insight to the photo-physics of phase change materials and highlight their potential in future opto-electronics.
关键词： Mixed-Mode Operation,Photothermal effects,Tuneable Photodetector,Phase Change Materials,Photoconductivity
更新于2025-09-10 09:29:36
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Concentration of defects responsible for persistent photoconductivity in Cu(In,Ga)Se2: Dependence on material composition
摘要： Persistent photoconductivity PPC in thin Cu(In,Ga)Se2 films is discussed within a model of relaxing defects acting as donors or acceptors depending on their configurational and charge state. The aim of this work is to identify the factors related to technological processes which affect the magnitude of PPC. We established a method of evaluation of the concentration of metastable defects in thin Cu(In,Ga)Se2 films relating it to the position of the Fermi level in thermodynamic equilibrium and used it to compare and discuss the impact of preparation details on the PPC value. The main result is that deviation from Cu/(Ga+In)Se2 stoichiometry does not change the concentration of metastable defects. Post deposition annealing in selenium affects the PPC depending on the presence of sodium during the treatment, while the impact of sodium itself on the metastable defect concentration apparently depends on whether it is present during the Cu(In,Ga)Se2 deposition process or whether it is supplied during post-deposition treatment.
关键词： Thin films,Photoconductivity,Copper indium gallium selenide,Metastability,Defects
更新于2025-09-09 09:28:46
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Disorder effect on photoconductivity properties in metallic Pb<sub>1-x</sub>Eu<sub>x</sub>Te epitaxial layers
摘要： In this work, we present photoconductivity measurements performed on metallic p-type Pb1-xEuxTe epitaxial films for x~ 0.02 and x~0.03 in the temperature range of 77K – 300K. The results show that sample with x~ 0.02 presented negative photoconductivity effect in the whole range of temperatures measured, while sample with x~0.03 presented a transition from positive to negative photoconductivity. Hall measurements were also performed to investigate the effects observed in both samples, but could not give any conclusive explanation. On the other hand, we showed that disorder changes considerably the generation/recombination ratios as temperature is varied giving rise to the anomalous effects observed.
关键词： disorder,PbEuTe,Photoconductivity
更新于2025-09-09 09:28:46
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Modular time division multiplexer: Efficient simultaneous characterization of fast and slow transients in multiple samples
摘要： A modular time division multiplexer (MTDM) device is introduced to enable parallel measurement of multiple samples with both fast and slow decay transients spanning from millisecond to month-long time scales. This is achieved by dedicating a single high-speed measurement instrument for rapid data collection at the start of a transient, and by multiplexing a second low-speed measurement instrument for slow data collection of several samples in parallel for the later transients. The MTDM is a high-level design concept that can in principle measure an arbitrary number of samples, and the low cost implementation here allows up to 16 samples to be measured in parallel over several months, reducing the total ensemble measurement duration and equipment usage by as much as an order of magnitude without sacrificing fidelity. The MTDM was successfully demonstrated by simultaneously measuring the photoconductivity of three amorphous indium-gallium-zinc-oxide thin films with 20 ms data resolution for fast transients and an uninterrupted parallel run time of over 20 days. The MTDM has potential applications in many areas of research that manifest response times spanning many orders of magnitude, such as photovoltaics, rechargeable batteries, amorphous semiconductors such as silicon and amorphous indium-gallium-zinc-oxide.
关键词： fast and slow transients,a-IGZO,MTDM,modular time division multiplexer,amorphous indium-gallium-zinc-oxide,parallel measurement,photoconductivity
更新于2025-09-09 09:28:46
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Sign-alternating photoconductivity and magnetoresistance oscillations induced by terahertz radiation in HgTe quantum wells
摘要： We report on the observation of terahertz radiation induced photoconductivity and of terahertz analog of the microwave-induced resistance oscillations (MIRO) in HgTe-based quantum well (QW) structures of different width. The MIRO-like effect has been detected in QWs of 20 nm thickness with inverted band structure and a rather low mobility of about 3 × 105 cm2/V s. In a number of other structures with QW widths ranging from 5 to 20 nm and lower mobility we observed an unconventional nonoscillatory photoconductivity signal which changes its sign upon magnetic ?eld increase. This effect was observed in structures characterized by both normal and inverted band ordering, as well as in QWs with critical thickness and linear dispersion. In samples having Hall bar and Corbino geometries an increase of the magnetic ?eld resulted in a single and double change of the sign of the photoresponse, respectively. We show that within the bolometric mechanism of the photoresponse these unusual features imply a nonmonotonic behavior of the transport scattering rate, which should decrease (increase) with temperature for magnetic ?elds below (above) the certain value. This behavior is found to be consistent with the results of dark transport measurements of magnetoresistivity at different sample temperatures. Our experiments demonstrate that photoconductivity is a very sensitive probe of the temperature variations of the transport characteristics, even those that are hardly detectable using standard transport measurements.
关键词： HgTe quantum wells,terahertz radiation,magnetoresistance oscillations,bolometric mechanism,photoconductivity
更新于2025-09-04 15:30:14
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A new method of accurately measuring photoconductive performance of 4H-SiC photoconductive switches
摘要： A new method of accurately measuring the photoconductive performance of photoconductive semiconductor switch (PCSS) was proposed. By this method, we succeeded extracting the photoconductivity of 4H-SiC substrate free from the obstruction of parasitic inductance in the test circuit. Photoconductive performance of the PCSS were precisely measured, where a maximum on-state photoconductivity of 6.26 (Ω · m)?1, a minimum on-state resistivity of 0.16 Ω · m and an accurate minimum resistance of 1.71 Ω were obtained for SiC substrate. The quantitative relationship between the on-state resistance and the reciprocal of area of laser trigger region was proved. The performance of PCSSs can be continuously adjusted to adapt different application requirements just by changing the area of laser excitation region.
关键词： pulse-power system switches,silicon carbide,Photoconductive switch,on-state resistance,intrinsic photoconductivity
更新于2025-09-04 15:30:14
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Applicability of the thin-film approximation in terahertz photoconductivity measurements
摘要： Thin mesoporous photoconductive layers are critically important for efficient water-spitting solar cells. A detailed understanding of photoconductivity in these materials can be achieved via terahertz transient absorption measurements. Such measurements are commonly interpreted using the thin-film approximation. We compare this approximation with a numerical solution of the transfer function without approximations using experimental results for thin-film mesoporous tin oxide (SnO2) samples which range in thickness from 3.3 to 12.6 mm. These samples were sensitized with either a ruthenium polypyridyl complex or a porphyrin dye. The two sensitizers have markedly different absorption coefficients, resulting in penetration depths of 15 mm and 1 mm, respectively. The thin-film approximation results are in good agreement with the numerical work-up for the short penetration length dye. For the longer penetration length samples, the thin-film formula fails even for thicknesses of only 3 mm (cid:2) k/100. The imaginary part of the conductivity calculated using the thin-film formula was significantly larger in magnitude than the value without approximations. This discrepancy between the commonly used thin-film approximation and the numerical solution demonstrates the need for a careful analysis of the thin-film formula.
关键词： thin-film approximation,terahertz photoconductivity,mesoporous SnO2,ruthenium polypyridyl complex,porphyrin dye
更新于2025-09-04 15:30:14
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Study of spectral and recombination characteristics of HVPE GaN grown on ammono substrates
摘要： A comprehensive study of the bulk ~400 μm thick GaN samples, grown by HVPE technology on AT-GaN seeds, and containing different carbon doping is reported. Spectroscopy of point centres has been implemented by combining several contactless/optical techniques: time resolved photoluminescence (TR-PL), microwave probed photoconductivity (MW-PC) transient and pulsed-photo-ionization spectroscopy (PPIS) techniques, together with steady-state PL (SS-PL) and transmission spectral measurements. The dynamics of the non-radiative and radiative recombination dependent on the excess carrier density and incorporated carbon concentration has been revealed. The cross-section of the photon-electron interaction and broadening factors due to electron-phonon coupling have been evaluated for various centres. Profiling of the excess carrier decay transients by scanning a wafer-edge boundary has been employed for estimation of surface recombination velocity. The asymmetry of surface recombination in heavily carbon doped samples has been corroborated by SS-PL intensity changes when comparing spectra recorded by exciting the opposite wafer surfaces using UV light. It has been inferred that the surface and bulk non-radiative recombination with 70 ns carrier lifetime is efficient only within initial stages of MW-PC and TR-PL transients. Several traps, tentatively attributed to CNON, CN, CI, VGa point defects, have been deduced from pulsed photo-ionization spectroscopy. The CN defect appeared to be the most efficient in redistribution of the radiative recombination. For these centres, the parameters such as the photon-electron interaction cross-section, broadening factor due to electron-phonon coupling, and concentration have been evaluated for GaN samples, carbon doped with different levels. The CNVGa, CICGa, CGaVN complexes have also been implied by considering TR-PL and SS-PL spectra. The conversion from absorption to emission spectra has been revealed and explained based on van Roosbroeck-Shockley approach. The long-tail photoluminescence decay with durations up to tens of ms has been explained by nearly resonant photo-ionization and photoluminescence transitions in sequence of self-sustaining processes when local excitation travels by hopping over the re-absorption lengths.
关键词： Photo-ionization spectroscopy,Microwave probed photoconductivity transients,Photoluminescence spectroscopy,Carbon doped HVPE GaN,Surface recombination
更新于2025-09-04 15:30:14