Large Photoresponse Research Articles

Graphene electrode-enhanced InSe/WSe2 van der Waals heterostructure for high-performance broadband photodetector with imaging capabilities

2D vdWs heterostructure is realized as a powerful technique for tuning the optoelectronic properties and thus developing the future generation optoelectronic devices, especially for photodetectors. However, photodetectors based on 2D vdWs heterostructure suffer from responsivity, detectivity, and large photoresponse speed inhibits their applications in further diverse areas. Here, a graphene electrode-based InSe/WSe2 vdWs heterostructure is proposed aiming to develop a high-performance photodetector. Owing to the graphene electrode, the heterostructure devices build a strong electronic field at the surface of the InSe/WSe2 vdWs heterostructure. As a result, the device shows excellent optoelectronic characteristics such as broad band photoresponse ranging from 532 nm (visible) to 1100 nm (near infrared) including a high responsivity of 829.7 AW−1, a detectivity of 2.81×1014 Jones and a rapid photoresponse of 10 µs. Significantly, as presented photodetector device is applied in an imaging system, showcasing its capability for high-contrast photodetection. These findings highlight that the potential of graphene electrode integration in 2D vdWs heterostructure provides an effective roadmap for developing the advancing next generation of optoelectronic devices.

Acousto-Drag Photovoltaic Effect by Piezoelectric Integration of Two-Dimensional Semiconductors.

Light-to-electricity conversion is crucial for energy harvesting and photodetection, requiring efficient electron-hole pair separation to prevent recombination. Traditional junction-based mechanisms using built-in electric fields fail in nonbarrier regions. Homogeneous material harvesting under a photovoltaic effect is appealing but is only realized in noncentrosymmetric systems via a bulk photovoltaic effect. Here we report the realization of a photovoltaic effect by employing surface acoustic waves (SAWs) to generate zero-bias photocurrent in the conventional layered semiconductor MoSe2. SAWs induce periodic modulation to electronic bands and drag the photoexcited pairs toward the traveling direction. The photocurrent is extracted from a local barrier. The separation of generation and extraction processes suppresses recombination and yields a large nonlocal photoresponse. We distinguish the acousto-electric drag and electron-hole pair separation effect by fabricating devices of different configurations. The acousto-drag photovoltaic effect, enabled by piezoelectric integration, offers an efficient light-to-electricity conversion method, independent of semiconductor crystal symmetry.

Synthesis of 2D yttrium zinc oxide nanosheets via simple chemical route toward high performance Schottky diode based on large charge carriers density and photoresponsivity

Yttrium zinc oxide (Zn0.85Y0.15O) nanostructures were stoichiometrically prepared by co-precipitation method. XRD, EDX, XPS, SEM, and TEM spectroscopy were examined to investigate structure, composition, and morphological characteristics. The synthesized nanocomposite exhibited polycrystalline structure with small crystallite size ∼ 27 nm in which the particles appeared in sheets like shape with high atomic density on surface. The optical parameters including energy gap (Eg) and refractive index (n) were investigated from (T%) and (R%) measurements through wavelength range from 300–900 nm. Al/Y:ZnO/p-Si/Ag Schottky diode was fabricated using thermal evaporating technique and its current–voltage (I–V) was analyzed using different models. The photodiode showed non-ideal behavior with ideality factor greater than unity and small potential barrier. Under various illuminations, the photodiode has revealed high photosensitivity attributed to trapped charge carriers at the interface. The charge carrier density Nd and built-in voltage Vbi were estimated from Mott Schottky (M–S) function suggesting high Schottky diode efficiency.

Large‐Area Self‐Assembled Hexagonal Boron Nitride Nanosheet Films for Ultralow Dark Current Vacuum‐Ultraviolet Photodetectors

AbstractHexagonal boron nitride (hBN) is one of the most promising candidates for vacuum‐ultraviolet photodetectors (VUV PDs). However, the efficient and low‐cost fabrication of large‐area hBN‐PDs still encounters challenges. Herein, a cost‐effective route is proposed for fast and scalable fabrication of high‐performance VUV PDs via hBN nanosheet (BNNS) films. BNNSs are peeled from bulk hBN and self‐assembled into large‐area ordered films. In such PDs, junction barriers are present at the contact interfaces of BNNSs and give the PDs a “light‐induced reduction of junction barrier height” working mechanism. The number of junction barriers are qualitatively adjusted by designing the size of BNNSs to optimize the performance of the devices. The performance of ultralow dark current (0.27 pA@80 V), high detectivity (3.42 × 1011 Jones), and fast response speed (20.97/17.69 ms) for 185 nm VUV light is achieved by a fabricated PD. Analysis based on the Schottky contact model proves that the large photoresponse is mainly attributed to the reduction of the barriers and series resistance on illumination. Meanwhile, a physical model is established to describe the working process of such PDs, of which conductivity is dominated by the junction barriers. Besides, a flexible PD is also fabricated, depicting excellent stability, and robustness.

Temperature dependent charge carrier dynamics in 2D ternary Cu2MoS4 nanoflakes: An effect of electron-phonon coupling.

Two-dimensional transition metal chalcogenides (2D TMCs) like MoS2, WS2 etc., have established significant dominance in the field of nanoscience and nanotechnology, owing to their unique properties like strong light-matter interaction, high carrier mobility, large photo-responsivity etc. Despite the widespread utilization of these binary TMCs, their potential in the advancement of the optoelectronic research is limited due to the constraints in band tuning and charge carrier lifetime. To overcome these limitations, ternary transition metal chalcogenides have emerged as promising alternatives. Although, the optical properties of these materials have never been explored properly. Herein, we have investigated one such promising member of this group, Cu2MoS4 (CMS) using both steady state and time-resolved spectroscopic techniques. The material exhibits a broad range of visible light absorption, peaking at 576nm. Photoluminescence spectroscopy confirmed the presence of both band gap emission and trap state-mediated emissions. Transient absorption spectroscopy unraveled the excited state charge carrier dynamics of CMS in sub-ps timescale, upon irradiation of visible light. We found significant influence of the trap mediated recombination, while Auger process being dominant at high charge density. We extended our study in a wide temperature range (5-300K), which reveals the impact of electron-phonon coupling strength on the band gap and charge carrier dynamics of this material. This detailed study would draw more attention toward the unexplored optical properties of ternary 2D chalcogenides and will open new avenues for the construction of 2D material-based optical devices.

High photoresponsivity MoS2 phototransistor through enhanced hole trapping HfO2 gate dielectric

Phototransistor using 2D semiconductor as the channel material has shown promising potential for high sensitivity photo detection. The high photoresponsivity is often attributed to the photogating effect, where photo excited holes are trapped at the gate dielectric interface that provides additional gate electric field to enhance channel charge carrier density. Gate dielectric material and its deposition processing conditions can have great effect on the interface states. Here, we use HfO2 gate dielectric with proper thermal annealing to demonstrate a high photoresponsivity MoS2 phototransistor. When HfO2 is annealed in H2 atmosphere, the photoresponsivity is enhanced by an order of magnitude as compared with that of a phototransistor using HfO2 without annealing or annealed in Ar atmosphere. The enhancement is attributed to the hole trapping states introduced at HfO2 interface through H2 annealing process, which greatly enhances photogating effect. The phototransistor exhibits a very large photoresponsivity of 1.1 × 107 A W−1 and photogain of 3.3 × 107 under low light illumination intensity. This study provides a processing technique to fabricate highly sensitive phototransistor for low optical power detection.

Enhanced photovoltaic and piezo-photovoltaic effects in flexible oxide ferroelectric film directly coated on polyimide substrate

Flexible ferroelectric photovoltaic (FePV) films have drawn widespread attention. However, in addition to the low filling factor (FF) and large bandgap of ferroelectrics, the direct fabrication of oxide FePV film on polymer substrate is also a challenging research topic. Here, we demonstrate high-performance FePV devices can be obtained with partially crystallized Zn0.92-xCux(Fe0.04Li0.04)O (ZCFLO) film directly coted on polyimide substrate utilizing a cheap and simple dip-coating method at low-temperature processing. By introducing the local ferroelectricity and the piezo-photovoltaic effect, enhanced carrier transportation is achieved in designed ferroelectric/amorphous nanostructures, and the photovoltaic performances of the ZCFLO devices are enhanced in broadened spectral range. Under the AM 1.5 G light and the tensile strain of 0.39%, the markedly improved FF (> 86%), large photoresponse (>15 mA/W), giant piezo-photovoltaic (PPV) tensor (∼1.94 mA∙W−1∙GPa−1) and resulted high PCE (>2.9%) were obtained in flexible ZCFLO (x = 0.05) FePV devices. This work not only offers a cost-efficient pathway to design high-performance FePV devices but also further broadens the research scope of piezo-phototronics.

High-Performance Planar Field-Emission Photodetector of Monolayer Tungsten Disulfide with Microtips.

Monolayer tungsten disulfide (ML WS2 ) is believed as an ideal photosensitive material due to its small direct bandgap, large exciton/trion binding energy, high carrier mobility, and considerable quantum conversion efficiency. Compared with other photosensitive devices, planar field emission (FE)-type photodetectors with a full-plane structure should simultaneously have rapider switching speed and lower power consumption. In this work, ML WS2 microtips are fabricated by electron beam lithography (EBL) way and used to construct a planar FE-type photodetector. By optimization design, ML WS2 with three microtips can exhibit the maximum current density as high as 52 A cm-2 (@300V µm-1 ), and the largest photoresponsivity is up to 6.8 × 105 A W-1 under green light irradiation, superior to that of many other ML transition metal dichalcogenide (TMDC) detectors. More interestingly, ML WS2 devices with microtips can effectively solve the contradictory problem between large photoresponsivity and rapid switching speed. The excellent photoresponse performances of ML WS2 with microtips should be attributed to their high carrier mobility, sharp emission edge, ultrahigh quantum yield, and unique planar FE device structure. Ourresearch may shed new light on exploring the fabrication technology and photosensitive mechanism of two dimensional (2D) material-based planar FE photodetectors.

Controllable Synthesis, Polar Behavior and Photoelectric Properties of BiOCl Microplates

Bismuth oxychloride (BiOCl) square microplates were prepared via a facile hydrothermal method. The X-ray diffraction patterns of the samples reveal a tetragonal BiOCl phase, and the scanning electron microscopy images show plate-like structures with large lateral size of 3~6 μm and thickness in the range of 100~300 nm. The effects of surfactant, reaction temperature and duration on the morphology of BiOCl powders are systematically investigated. The polar behavior of a BiOCl single-crystalline microplate is examined by using piezoresponse force microscopy evidenced over 80 pm displacement under 40 V bias voltage. In addition, the photoelectric performance of the BiOCl microplates is evaluated by using electrochemical workstation with three-electrode system, and large photocurrent densities (over 0.5 μA/cm2) and fast photoresponse (0.7~1.1 s) are detected by applying both 365 nm monochromatic light and sunlight illumination. The surface potential changes of BiOCl microplate under different light condition, characterized by in-situ Kelvin probe force microscopy, further verify the separation ability of the photo-induced charge carriers. These findings would be beneficial for further design photocatalytic and piezocatalytic materials.

Ab initio study of the nonlinear optical properties and dc photocurrent of the Weyl semimetal TaIrTe4

The type-II Weyl semimetal TaIrTe${}_{4}$ exhibits one of the largest nonlinear photoresponses measured to date [Ma $e\phantom{\rule{0}{0ex}}t$ $a\phantom{\rule{0}{0ex}}l$., Nature Materials 18, 476 (2019)]. The present work provides theoretical calculations on several competing candidate effects that can account for it. The third-order contribution known as the jerk current matches the measured magnitude of the photocurrent as well as its angular distribution. The origin of the large photoresponse is traced back to a constructive interference between the effective mass and the dipole matrix element of the Weyl bands crossing the Fermi level.

Facile and Effective Band Gap Engineering of 2D Ruddlesden–Popper Perovskites with Improved Structural and Optoelectronic Properties

Incorporation of alkali metal ions (Li+, Na+, K+, Rb+, and Cs+) into 3D metal-halide perovskite crystal structures has resulted in improved crystallinity and film morphology, reduced trap density, and enhanced charge carrier transport. However, due to intrinsic structural instability associated with 3D perovskites, their alkali metal ion-doped semiconductors are not a suitable option for real device optoelectronics. In recent years, Ruddlesden–Popper (RP)-phase quasi-two-dimensional (2D) metal halide perovskites have drawn considerable attention due to their tunable energy band gap, large electron and hole diffusion lengths (∼10 μm), and lower recombination rates compared to pristine 2D metal halide perovskites (n = 1). However, alkali metal ion-incorporated RP perovskite systems are not explored much; therefore, we demonstrate the incorporation of Rb+, using the RbI precursor, into the quasi-2D RP perovskite (BA)2(MA)Pb2Br7 (BA = C4H9NH3; MA = CH3NH3), which has also resulted in the successive replacement of Br– with I– in the PbBr6 network. Subsequent replacement of Br– with I– finely tuned the energy band gap from 2.92 to 2.43 eV, while keeping the phase of the pristine lead bromide RP perovskite intact, as confirmed by X-ray diffraction investigations. MA+ cations available at the outer edge sites got partially exchanged with Rb ions, which in turn has regulated the perovskite crystal growth, whereas the excess Rb+ alloyed with replaced Br– to form RbBr, which resulted in the formation of thinner grain boundaries and thus showed improved charge transport. Transient photocurrent measurements performed for RbI-doped perovskites (lateral configuration photodetector: fluorine-doped tin oxide (FTO)/RP-perovskite/FTO of channel width ∼150 μm), for 35 cycles under standard Xe-lamp (100 mW/cm2) illumination, have shown strong and fast photocurrent response with large photoresponsivity (3.92 × 10–4 A/W). Comparison of structural, optical, and optoelectronic properties of RbI-doped RP perovskites is carried out with the mixed RP perovskites and has further confirmed that Rb+ incorporation plays an important role in enhancing the crystal growth.

Multifunctional l-tryptophan derivative induced surface passivation for lateral perovskite photodetectors

Organic-inorganic hybrid perovskites have already been employed as promising light-sensitive materials for high-performance photodetectors (PDs) due to their intriguing optoelectronic features. Nonetheless, such perovskite-based PDs often suffer from low sensitivity, high dark current and inevitable degradation. In this work, a novel multifunctional molecule l-tryptophan ethyl ester hydrochloride (l-TEEH) was used to treat the surface defects of triple-cation mixed halide perovskite film. It is found that the modulator with multiple functional groups can effectively passivate the uncoordinated ions (Pb2+ and I-) and halide (I and Cl) vacancies of the perovskite film. Owing to the reduced defects, the dark current of the pristine perovskite PD significantly decreases from ∼ 10-9 A to ∼ 10-11 A after the l-TEEH treatment. Moreover, the perovskite PD with the l-TEEH treatment exhibits a large photoresponsivity (1.27 A/W) and an ultrahigh on/off ratio (∼9 × 103). More impressively, the optimized device shows excellent stability in air with a relative humidity of 40–50 %. Furthermore, the reliable imaging capability of perovskite device with the l-TEEH treatment is also successfully demonstrated.

Electronic transport and polarization-dependent photoresponse in few-layered hafnium trisulfide (HfS3) nanoribbons

Few-layered HfS3 nanoribbons exhibit n-type conductivity and a large photoresponse to visible light. The photocurrent strongly depends on the polarization direction of the excitation laser due to the highly anisotropic quasi-1D crystal structure of HfS3.

Thickness dependent wavelength selective NIR-UV-visible photoresponse in ZnO nanowires and silicon heterojunction

In this paper, we report ZnO nanowires (NWs) and silicon-based type-II PN heterojunction for UV–Visible–Infrared self-powered photodetection. The as-grown ZnO NWs were highly crystalline and aligned along the c-axis in the [002] direction revealed in the HRTEM and XRD measurements. The Hall measurements revealed the n-type behavior for ZnO and p-type for p-Si with carrier concentrations of 4.09 × 1016 cm−3 and 1.38 × 1017 cm−3, respectively. The depletion widths were estimated to be ∼35 nm and ∼120 nm, respectively for p-Si and n-ZnO NWs. The Ag/n-ZnO NWs/p-Si/Ag PN heterojunction showed large photoresponse, even at zero bias, under the illumination of commercially available UV–Visible–NIR LEDs, thus acting as a self-powered photodetector. It was interesting to observe that the photoresponse was dependent on the growth time and hence the thickness of ZnO NWs thin film. A maximum zero bias responsivity of ∼0.1 A/W at green (515 nm) was observed and was large for the junction with thicker ZnO NWs film (5 h growth), compared with thinner (3 h growth) device under IR (950 nm) LED illumination, however, it was observed otherwise for UV (395 nm) LED. This suggests that tuning the thickness of the ZnO NWs thin film results in the wavelength selective photoresponse, consequently, paving the way towards UV blind IR-visible photodetector based on ZnO NWs. The transient short circuit current (Isc vs t) and open circuit voltage (Voc vs t) properties showed fast and large responses under periodic illumination of all LEDs (UV–Vis–NIR). The response was observed to depend on the intensity of light and the maximum Voc comes out to be ∼102 mV and Isc ∼5.58 μA, under the illumination of a red laser diode.

Suppressing the Multiple Nucleation for the Uniform Growth of Perovskite Single‐Crystal Microplates Arrays toward High‐Performance Optoelectronic Devices

AbstractThe pursuit of high‐performance and integrated perovskite optoelectronic devices drives the development of efficient methods to pattern perovskite single crystals (PSCs). However, due to stochastic and multiple nucleation, PSCs obtained from traditional patterning methods still suffer from heterogeneous morphology and low crystallinity, resulting in unwanted large variation in the device performance. Herein, an effective and universal strategy is reported for the large‐scale patterned growth of high‐quality perovskite single‐crystal microplates with uniform size and thickness. By modulating the wettability of gold nanoparticles, nucleation energetic barriers are subtly regulated and thus intractably random and multiple nucleation are fundamentally suppressed, enabling the formation of homogeneous perovskite microplates with exceptional properties in terms of ultralow surface defect density (6.1 × 107 cm−2) and high carrier mobility (176 cm2 V−1 s−1). In consequence, the photodetector array based on the patterned perovskite microplates exhibits a large photoresponsivity up to 615 A W−1, along with a low photocurrent variable coefficient <5.2%, which enables the realization of ultrasensitive and high‐contrast imaging functions. This patterning technique constitutes a major step toward the deployment of PSCs in integrated optoelectronic devices.

Broadband Photodetection of Cd3As2: Review and Perspectives

Due to the topologically protected gapless electronic structure, Cadmium arsenide (Cd3As2) is predicted to possess large and high-speed photoresponses in a broad spectrum. The progressively developed device process and material technologies offer the possibility to integrate semimetals with semiconductors or 2D materials into heterojunctions, which can suppress the intrinsically high dark current. Hence, photodetectors based on Cd3As2 and its heterostructures has been gradually evolved in recent years, showing an excellent broadband photodetection capability. In this Perspective, we elaborate on several key parameters for evaluating the performance of a photodetection. We overview recent studies on photodetection and imaging based on Cd3As2 nanostructures or thin films, and further discuss the opportunities and challenges for Cd3As2 photodetectors.

Co-sputtering deposition of high-photoresponsivity and high-mobility polycrystalline BaSi2 films on Si substrates

• Stoichiometric BaSi 2 films were obtained by co-sputtering from BaSi 2 and Ba targets. • Power applied on the targets controlled the Ba and Si species reaching the substrate. • Deposition without Ba target resulted in Ba-deficient films. • Large photoresponsivity was observed in spite of polycrystalline films. Barium disilicide (BaSi 2 ) has shown great promise for solar cell applications. Recent studies have revealed that defects such as Si vacancies in BaSi 2 films caused by the Ba/Si atomic ratios being away from stoichiometry degrade the electrical and photoresponse properties of BaSi 2 films. The formation of BaSi 2 films by sputtering has been performed using basically one BaSi 2 target, which makes it difficult to control the Ba/Si atomic ratio of the grown films. In this work, we investigate the formation of BaSi 2 films on Si(111) substrates by radio-frequency (RF) sputtering of BaSi 2 and Ba targets, and independently control the RF powers set on the targets. It is found that the contribution of sputtering the Ba target to the BaSi 2 growth rate ( GR Ba / GR BaSi2 ) can be used to find the growth conditions for high-photoresponsivity BaSi 2 films. The highest photoresponsivity reached 1.4 A W −1 at room temperature for BaSi 2 films grown at 600°C when a bias voltage of 0.5 V was applied between the front indium tin oxide electrodes and rear Al electrodes. The electron mobility depended on sputtering conditions, but mostly exceeded 1000 cm 2 V −1 s −1 in spite of randomly oriented polycrystalline films. These values are comparable to those obtained for BaSi 2 epitaxial films on Si(111) by molecular beam epitaxy.

The High Photoresponse of Stress‐Tuned MoTe2 Optoelectronic Devices in the Telecommunication Band

There are attractive prospects to achieve large photocurrent and high optical response in telecommunication wavelengths for optoelectronic devices. Inspired by the recent experiment [Nat. Photonics 2020, 14, 578], the photocurrent of the devices composed of noncentral inversion symmetric monolayer MoTe2 along the armchair direction under different linearly polarized light by the quantum transport calculation is investigated. The results demonstrate that the maximum photocurrent will increase under the biaxial tensile stress, and importantly, the peak of photocurrent will move toward the direction of lower photon energy owing to the reduction of the bandgap of monolayer MoTe2, which is opposite to the case of applying the bias voltage. Ultimately, it is proved that monolayer MoTe2 devices with large photoresponse can be tuned to the interesting telecommunication band via the imposition of biaxial stress and bias voltage, which makes the devices have potential applications in the field of silicon photonics.

SnS Nanoflakes/Graphene Hybrid: Towards Broadband Spectral Response and Fast Photoresponse.

High responsivity has been recently achieved in a graphene-based hybrid photogating mechanism photodetector using two-dimensional (2D) semiconductor nanosheets or quantum dots (QDs) sensitizers. However, there is a major challenge of obtaining photodetectors of fast photoresponse time and broad spectral photoresponse at room temperature due to the high trap density generated at the interface of nanostructure/graphene or the large band gap of QDs. The van der Waals interfacial coupling in small bandgap 2D/graphene heterostructures has enabled broadband photodetection. However, most of the photocarriers in the hybrid structure originate from the photoconductive effect, and it is still a challenge to achieve fast photodetection. Here, we directly grow SnS nanoflakes on graphene by the physical vapor deposition (PVD) method, which can avoid contamination between SnS absorbing layer and graphene and also ensures the high quality and low trap density of SnS. The results demonstrate the extended broad-spectrum photoresponse of the photodetector over a wide spectral range from 375 nm to 1550 nm. The broadband photodetecting mechanisms based on a photogating effect induced by the transferring of photo-induced carrier and photo-hot carrier are discussed in detail. More interestingly, the device also exhibits a large photoresponsivity of 41.3 AW−1 and a fast response time of around 19 ms at 1550 nm. This study reveals strategies for broadband response and sensitive photodetectors with SnS nanoflakes/graphene.

Enhanced photogalvanic effect in a 2D ferroelectric ZrI2 by interlayer sliding

Two-dimensional ferroelectrics with moderate band gap enable unprecedented applications in optoelectronics. Here, we report that the photogalvanic effect (PGE) of narrow-band-gap semiconductor bilayer ZrI2 is significantly enhanced by the interlayer sliding which turns out to be ferroelectric with both in-plane and out-of-plane polarizations. The intrinsic ferroelectric field promotes the separation efficiency of photogenerated carriers and reduces the recombination rate of electron–hole pairs, thus improving the photoelectric conversion efficiency and resulting in a larger photoresponse. The magnitude of the maximum photoresponse in the bilayer β-ZrI2 (ferroelectric) is enhanced by about 5 times than in the bilayer s-ZrI2 (paraelectric). A robust broadband photoresponse from mid-infrared to visible can be found from its photodetector. Our results provide great insights to engineering novel optoelectronic applications by ferroelectric slidetronics.