Heterostructure Photodetector Research Articles

Selectively Modulated Photoresponse in Type‐I Heterojunction for Ultrasensitive Self‐Powered Photodetectors

AbstractPhotodetectors based on two‐dimensional (2D) van der Waals heterostructures (vdWHs) have demonstrated great potential in modern nanotechnologies across a wide range of applications. However, due to the severe interface recombination of the photogenerated electron–hole pairs and various absorption edges of constituent layers, they would suffer from low carrier collection efficiency, and the spectral response range of each constituent layer is indistinguishable. Herein, tellurium (Te) nanoflakes with broadband photoresponse are synthesized to construct type‐I InSe/Te vdWHs photodetector, which exhibits an ultralow reverse dark current of 3 × 10−14 A and an ultrahigh current rectification ratio of 108. Moreover, considerable photovoltaic effect of the heterostructure device is observed under illumination, attaining a light on/off ratio of up to 105, a high specific detectivity of 1.77 × 1011 Jones, and a fast response time of 320 µs. Based on type‐I band alignment, the Te layer can collect the photogenerated holes from the InSe layer to suppress the recombination of photogenerated carriers. More importantly, the spectral response of the InSe/Te heterostructure photodetector can be selectively modulated by the InSe layer. This work demonstrates that band alignment engineering of 2D vdWHs holds great potential for developing high‐performance self‐powered photodetectors.

Role of Surface Adsorbates on the Photoresponse of (MO)CVD-Grown Graphene-MoS2 Heterostructure Photodetectors.

A promising strategy toward ultrathin, sensitive photodetectors is the combination of a photoactive semiconducting transition-metal dichalcogenide (TMDC) monolayer like MoS2 with highly conductive graphene. Such devices often exhibit a complex and contradictory photoresponse as incident light can trigger both photoconductivity and photoinduced desorption of molecules from the surface. Here, we use metal-organic chemical vapor deposition (MOCVD) to directly grow MoS2 on top of graphene that is deposited on a sapphire wafer via chemical vapor deposition (CVD) for realizing graphene-MoS2 photodetectors. Two-color optical pump-electrical probe experiments allow for separation of light-induced carrier transfer across the graphene-MoS2 heterointerface from adsorbate-induced effects. We demonstrate that adsorbates strongly modify both magnitude and sign of the photoconductivity. This is attributed to a change of the graphene doping from p- to n-type in case adsorbates are being desorbed, while in either case, photogenerated electrons are transferred from MoS2 to graphene. This nondestructive probing method sheds light on the charge carrier transfer mechanisms and the role of adsorbates in two-dimensional (2D) heterostructure photodetectors.

Vertical Schottky ultraviolet photodetector based on graphene and top–down fabricated GaN nanorod arrays

GaN has been widely used in the fabrication of ultraviolet photodetectors because of its outstanding properties. In this paper, we report a graphene–GaN nanorod heterostructure photodetector with fast photoresponse in the UV range. GaN nanorods were fabricated by a combination mode of dry etching and wet etching. Furthermore, a graphene–GaN nanorod heterostructure ultraviolet detector was fabricated and its photoelectric properties were measured. The device exhibits a fast photoresponse in the UV range. The rising time and falling time of the transient response were 13 and 8 ms, respectively. A high photovoltaic responsivity up to 13.9 A/W and external quantum efficiency up to 479% were realized at the UV range. The specific detectivity D * = 1.44 × 1010 Jones was obtained at –1 V bias in ambient conditions. The spectral response was measured and the highest response was observed at the 360 nm band.

Manipulating Picosecond Photoresponse in van der Waals Heterostructure Photodetectors

AbstractSelf‐powered ultrafast 2D photodetectors have demonstrated great potential in imaging, sensing, and communication. Understanding the intrinsic ultrafast charge carrier generation and separation processes is essential for achieving high‐performance devices. However, probing and manipulating the ultrafast photoresponse is limited either by the temporal resolution of the conventional methods or the required sophisticated device configurations. Here, van der Waals heterostructure photodetectors are constructed based on MoS2/WSe2 p–n and n–n junctions and manipulate the picosecond photoresponse by combining photovoltaic (PV) and photothermoelectric (PTE) effects. Taking time‐resolved photocurrent (TRPC) measurements, a TRPC peak at zero time delay is observed with decay time down to 4 ps in the n–n junction device, in contrast to the TRPC dip in the p–n junction and pure WSe2 devices, indicating an opposite current polarity between PV and PTE. More importantly, with an ultrafast photocurrent modulation, a transition from a TRPC peak to a TRPC dip is realized, and detailed carrier transport dynamics are analyzed. This study provides a deeper understanding of the ultrafast photocurrent generation mechanism in van der Waals heterostructures and offers a new perspective in instruction for designing more efficient self‐powered photodetectors.

Self-powered topological insulator Bi2Te3/Ge heterojunction photodetector driven by long-lived excitons transfer

Due to the wide spectral absorption and ultrafast electron dynamical response under optical excitation, topological insulator (TI) was proposed to have appealing application in next-generation photonic and optoelectronic devices. Whereas, the bandgap-free speciality of Dirac surface states usually leads to a quick relaxation of photoexcited carriers, making the transient excitons difficult to manipulate in isolated TIs. Growth of TI Bi2Te3/Ge heterostructures can promote the specific lifetime and quantity of long-lived excitons, offering the possibility of designing original near-infrared optoelectronic devices, however, the construction of TI Bi2Te3/Ge heterostructures has yet to be investigated. Herein, the high-quality Bi2Te3/Ge heterojunction with clear interface was prepared by physical vapor deposition strategy. A significant photoluminescence quenching behaviour was observed by experiments, which was attributed to the spontaneous excitation transfer of electrons at heterointerface via theoretical analysis. Then, a self-powered heterostructure photodetector was fabricated, which demonstrated a maximal detectivity of 1.3 × 1011 Jones, an optical responsivity of 0.97 A W−1, and ultrafast photoresponse speed (12.1 μs) under 1064 nm light illumination. This study offers a fundamental understanding of the spontaneous interfacial exciton transfer of TI-based heterostructures, and the as-fabricated photodetectors with excellent performance provided an important step to meet the increasing demand for novel optoelectronic applications in the future.

Sulfide‐Inhibiting Growth of Lead Sulfide Rods Array Film from Micron to Nano for NIR Photodetector

In general, the growth rate of lead sulfide (PbS) crystals in the solution is fast, and it is difficult to obtain nanosized structure films without the presence of inhibitors. Herein, highly crystalline 1D single‐crystal PbS nanorods array on the graphene substrate is prepared in the solution containing a high‐concentration sulfur ion as the inhibitors by electrochemical atomic layer epitaxy (ECALE) method. Meanwhile, the diameter of the PbS array from micrometers to nanometers can be controlled by adjusting the ratio of lead and sulfur. Through polarization studies on graphene substrates, the critical role of Au–thiolate in the vertical growth of PbS nanorod is controlled. Finally, the PbS array–graphene heterostructure photodetector presents an extraordinary photoresponsivity in 1.55 μm at room temperature.

High-Performance Photodetectors Based on MoTe2-MoS2 van der Waals Heterostructures.

Two-dimensional (2D) materials have got extensive attention for multifunctional device applications in advanced nanoelectronics and optoelectronics, such as field-effect transistors, photodiodes, and solar cells. In our work, we fabricated MoTe2–MoS2 van der Waals heterostructure photodetectors with great performance using the mechanical exfoliation method and restack technique. It is demonstrated that our MoTe2–MoS2 heterostructure photodetector device can operate without bias voltage, possessing a low dark current (10 pA) and high photocurrent on/off ratio (>104). Importantly, the room temperature photoresponsivity of the MoTe2–MoS2 photodetector can reach 110.6 and 9.2 mA W–1 under λ = 532 and 1064 nm incident laser powers, respectively. Our results indicate that the van der Waals heterostructure based on 2D semiconducting materials is expected to play an important role in nanoscale optoelectronic applications.

Spectral response optimization in Pentacene and cupric oxide-based photodetector using structural engineering: Planar and bulk heterostructure

This research focuses on the performance analysis of planar and bulk heterostructure photodetector based on Pentacene and cupric oxide (CuO) for an optimized spectral response. Planar structure ITO/PEDOT:PSS/Pentacene/CuO/Al and bulk-heterostructure ITO/PEDOT:PSS/Pentacene:CuO/Al are compared for the analysis. The research is based on the structure's optical and electrical properties. It was discovered that the devices perform admirably in terms of spectral response range, spanning from UV (ultraviolet)-to-NIR (near-infrared). Also, the carrier transport mechanism employs a photomultiplication process, which results in high external quantum efficiency (EQE). For the photodetectors under analysis, the bulk heterostructure device is recognized to have the best UV and NIR spectral performance, while the planar heterostructure device shows the best visible (Vis) spectral response. This illustrates that structural engineering can be opted in such kind of photodetectors for an optimized spectral response.

Facile, Real‐Time Identification of Blood Components with Self‐Powered Organic–Inorganic Heterostructure Photodetectors

AbstractA rapid and efficient opto‐electrical method for the determination of blood components is demonstrated through a tin oxide (SnO2) quantum dot (QD) fluorene copolymer heterojunction photodetector (FP‐PD). The photo‐active materials, the device structure, and the sensing system are carefully designed to provide miniaturization at a low cost. SnO2 QDs are synthesized with a one‐step solvothermal reaction and a photodetector, and then fabricated in a simple sequential spin‐coating process. Under optimal conditions, the SnO2 QD/FP‐PD shows remarkable responsivity, detectability, fast responses, and stability under self‐powered operation. In this research, optical characteristics of blood components, and interactions between the photodetector and blood components from illuminating two different wavelengths of ultraviolet light, are systemically investigated. Furthermore, three different blood component mixtures are successfully determined by the SnO2 QD/FP‐PD based on specific absorption phenomena, which provides a simple and efficient technique for emergency medical care and health monitoring systems.

Two-Dimensional Cs2AgBiBr6/WS2 Heterostructure-Based Photodetector with Boosted Detectivity via Interfacial Engineering.

Two-dimensional (2D) transition metal dichalcogenide (TMDC) monolayers have been widely used for optoelectronic devices because of their ultrasensitivity to light detection acquired from their direct gap properties. However, the small cross-section of photon absorption in the atomically thin layer thickness significantly limits the generation of photocarriers, restricting their performance. Here, we integrate monolayer WS2 with 2D perovskites Cs2AgBiBr6, which serve as the light absorption layer, to greatly enhance the photosensitivity of WS2. The efficient charge transfer at the Cs2AgBiBr6/WS2 heterojunction is evidenced by the shortened photoluminescence (PL) decay time of Cs2AgBiBr6. Scanning photocurrent microscopy of Cs2AgBiBr6/WS2/graphene reveals that improved charge extraction from graphene leads to an enhanced photoresponse. The 2D Cs2AgBiBr6/WS2/graphene vertical heterostructure photodetector exhibits a high detectivity (D*) of 1.5 × 1013 Jones with a fast response time of 52.3 μs/53.6 μs and an on/off ratio of 1.02 × 104. It is worth noting that this 2D heterostructure photodetector can realize self-powered light detection behavior with an open-circuit voltage of ∼0.75 V. The results suggest that the 2D perovskites can effectively improve the TMDC layer-based photodetectors for low-power consumption photoelectrical applications.

Chemical vapor deposited WS2/MoS2 heterostructure photodetector with enhanced photoresponsivity

Two-dimensional transition metal dichalcogenides (TMDCs) have attracted great interest due to their unique semiconductor properties. Among all TMDC materials, MoS2 and WS2 are promising for composing heterostructures. However, traditional TMDC heterostructure fabrication depends on transfer process, with drawbacks of interface impurity and small size. In this work, a two-step chemical vapor deposition (CVD) process was applied to synthesize large-scale WS2/MoS2 heterostructure. Surface morphology and crystal structure characterizations demonstrate the high-quality WS2/MoS2 heterostructure. The WS2/MoS2 heterostructure photodetector fabricated by photolithography exhibits an enhanced photoresponsivity up to 370 A W−1 in comparison with single WS2 or MoS2 devices. This study suggests a direct CVD growth of large-scale TMDC heterostructure films with clean interface. The built-in electric field at interface contributes to the separation of photo-generated electron–hole pairs, leading to enhanced photocurrent and responsivity, and showing promising potentials in photo-electric applications.

Simultaneous visible and ultraviolet photoresponse improvement of MoS2/ZnO heterostructure photodetector via direct resonant coupling of Au nanoparticles localized surface plasmon resonance

Localized surface plasmon resonance (LSPR) as a unique property of metal nanoparticles (NPs) has been widely applied to enhance the performance of optoelectronic devices. However, limited by the specific resonance frequency of plasmonic NPs, the LSPR of NPs can only improve the photoresponse performance of photodetectors at specific wavelength. In this work, a simple strategy is proposed to simultaneously improve the performance of the p-MoS2/n-ZnO heterostructure photodetector in visible and ultraviolet (UV) light regions by modifying Au NPs. The Ilight/Idark ratio of the photodetector is considerably increased after the functionalization with plasmonic Au NPs under visible and UV light illumination due to the direct resonant coupling of LSPR. In particular, the photocurrent of the photodetector increases 14.8 times after Au NPs modification under 532 nm illumination, giving rise to an obvious increase in responsivity, external quantum efficiency and specific detectivity. Moreover, the modification of Au NPs facilitates the rapid separation of electrons and holes due to the generation of surface depletion regions located at Au/MoS2 and Au/ZnO interfaces. Consequently, the photoresponse speed is also drastically improved after Au NPs decoration in both visible and ultraviolet light regions. The strategy of direct resonant coupling of Au NPs LSPR with two photosensitive materials proposed in this work will provide a new avenue for optimizing the performance of optoelectronic devices.

Self-powered semitransparent/flexible doped-graphene/WS2 vertical-heterostructure photodetectors

A combination of semi-metallic graphene and photosensitive two-dimensional (2D) transition metal dichalcogenide for heterostructures is ideal for high-performance optoelectronic device applications. Here, we first report semitransparent/flexible photodetectors (PDs) employing trifluoromethanesulfonyl-amide (TFSA)-doped graphene (GR) (TFSA-GR)/WS2 vertical heterostructures. The TFSA-GR/WS2 PDs show a delta-function-like photo-/dark-current (or on/off) ratio-vs-voltage behavior at zero bias, irrespective of wavelength (λ), meaning “self-powered”, mainly resulting from the surface doping of GR. The photoresponse is very sensitive in a wide ultraviolet-to-visible λ range. Maximum key figures of merit obtained for the PDs: responsivity (R), external quantum efficiency, and detectivity are 0.14 AW−1, 40%, and 2.5 × 109 cm Hz1/2 W−1, respectively, comparable to or even larger than those of previously-reported self-powered and/or hetero-structured PDs. The average transmittance of the PDs in the visible region is about 40%, indicating their semitransparency. The PDs maintain 88% of the initial R even after bending tests at 4 mm bending radius for 3000 cycles, demonstrating the excellent flexibility.

High-performance near-infrared photodetectors based on gate-controlled graphene–germanium Schottky junction with split active junction

Abstract The structure of a gate-controlled graphene/germanium hybrid photodetector was optimized by splitting the active region to achieve highly sensitive infrared detection capability. The strengthened internal electric field in the split active junctions enabled efficient collection of photocarriers, resulting in a responsivity of 2.02 A W−1 and a specific detectivity of 5.28 × 1010 Jones with reduced dark current and improved external quantum efficiency; these results are more than doubled compared with the responsivity of 0.85 A W−1 and detectivity of 1.69 × 1010 Jones for a single active junction device. The responsivity of the optimized structure is 1.7, 2.7, and 39 times higher than that of previously reported graphene/Ge with Al2O3 interfacial layer, gate-controlled graphene/Ge, and simple graphene/Ge heterostructure photodetectors, respectively.

Self-powered heterojunction photodetector based on thermal evaporated p-CuI and hydrothermal synthesised n-TiO2 nanorods

CuI film was grown by thermal evaporation technology on TiO2 nanorods array synthesized using a hydrothermal method, and a p-CuI/n-TiO2 heterostructure photodetector was constructed. The structure, morphology, light absorption, and photoresponse performance of the device were investigated. The heterojunction detector is self-powered and sensitive to light in the range of 320nm∼450nm. At 0V, the on/off ratio of the device is ∼770. The peak responsivity (0V, 410nm) is about 4.5mA/W and the peak detectivity is 1.08×1011 Jones. Also, the reproducibility and stability of the heterojunction photodetector are excellent. This work provides an effective route for the study of self-powered photodetectors.

Self-driven heterostructure photodetector of sputtered CZTS film on c-Si with an inverted pyramid structure

Ag has been incorporated into the CZTS film through post-doping by magnetron sputtering to decrease the CuZn anti-site defect. Efforts have been dedicated to optimize the Ag sputtering time and 60 s will be the best as surveyed from the SEM, XRD and Raman spectra. Then the broad-band self-driven heterostructure photodetector has been manufactured by combining the CZTS and inverted pyramid n-Si (IP n-Si). The device represents the first-rank property under the irradiation of 5 mW, 780 nm LED with 0 V bias with the responsivity and detectivity of 7.2 mA/W and 4.98 × 1010 Jones respectively. The device can persist excellent linearity when enduring a 40 mW-80 mW, 980 nm NIR laser with 0 V bias. The comprehensive performance becomes the best under the irradiation of a 50 mW laser. The responsivity and detectivity are 1.22 mA/W and 1.98 × 1010 Jones. The device can also work stably as the laser changes from 1 Hz to 15 kHz. The rise time and decay time are 93.3 μs and 141.0 μs respectively. These results open up an innovative application for CZTS to build a broad-band self-driven photodetector as a window-layer.

Energy-Band Engineering by Remote Doping of Self-Assembled Monolayers Leads to High-Performance IGZO/p-Si Heterostructure Photodetectors.

Metal oxide semiconductors are of great interest for enabling advanced photodetectors. However, operational instability and the absence of an appropriate doping technique hinder practical development and commercialization. Here, a strategy is proposed to dramatically increase the conventional photodetection performance, having superior stability in operational and environmental atmospheres. By performing energy-band engineering through an octadecylphosphonic acid (ODPA) self-assembled-monolayer-based doping treatment, the proposed indium-gallium-zinc oxide (IGZO)/p-Si heterointerface devices exhibit greatly enhance the photoresponsive characteristics, including a photoswitching current ratio with a 100-fold increase, and photoresponsivity and detectivity with a 15-fold increase each. The observed ODPA doping effects are investigated through comprehensive analysis with X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and Kelvin probe force microscopy (KPFM). Furthermore, the proposed photodetectors, fabricated at a 4 in. wafer scale, demonstrate its excellent operation robustness with consistent performance over 237 days and 20000 testing cycles.

Synthesis of vertically-aligned large-area MoS2 nanofilm and its application in MoS2/Si heterostructure photodetector

Van der Waals heterostructures based on the combination of 2D transition metal dichalcogenides and conventional semiconductors offer new opportunities for the next generation of optoelectronics. In this work, the sulfurization of Mo film is used to synthesize vertically-aligned MoS2 nanofilm (V-MoS2) with wafer-size and layer controllability. The V-MoS2/n-Si heterojunction was fabricated by using a 20 nm thickness V-MoS2, and the self-powered broadband photodetectors covering from deep ultraviolet to near infrared is achieved. The device shows superior responsivity (5.06 mA W−1), good photodetectivity (5.36 × 1011 Jones) and high on/off ratio I on/I off (8.31 × 103 at 254 nm). Furthermore, the V-MoS2/n-Si heterojunction device presents a fast response speed with the rise time and fall time being 54.53 ms and 97.83 ms, respectively. The high photoelectric performances could be attributed to the high-quality heterojunction between the V-MoS2 and n-Si. These findings suggest that the V-MoS2/n-Si heterojunction has great potential applications in the deep ultraviolet-near infrared detection field, and might be used as a part of the construction of integrated optoelectronic systems.

Hybrid 1D/2D heterostructure with electronic structure engineering toward high-sensitivity and polarization-dependent photodetector

The widespread application of photodetectors has triggered an urgent need for high-sensitivity and polarization-dependent photodetection. In this field, the two-dimensional (2D) tungsten disulfide (WS2) exhibits intriguing optical and electronic properties, making it an attractive photosensitive material for optoelectronic applications. However, the lack of an effective built-in electric field and photoconductive gain mechanism in 2D WS2 impedes its application in high-performance photodetectors. Herein, we propose a hybrid heterostructure photodetector that contains 1D Te and 2D WS2. In this device, 1D Te induces in-plane strain in 2D WS2, which regulates the electronic structures of local WS2 and gives rise to type-II band alignment in the horizontal direction. Moreover, the vertical heterojunction built of 2D WS2 and 1D Te introduces a high photoconductive gain. Benefiting from these two effects, the transfer of photogenerated carriers is optimized, and the proposed photodetector exhibits high sensitivity (photoresponsivity of ~27.7 A W−1, detectivity of 9.5 × 1012 Jones, and short rise/decay time of 19.3/17.6 ms). In addition, anisotropic photodetection characteristics with a dichroic ratio up to 2.1 are achieved. This hybrid 1D/2D heterostructure overcomes the inherent limitations of each material and realizes novel properties, opening up a new avenue towards constructing multifunctional optoelectronic devices.

Graphene/SnS2 van der Waals Photodetector with High Photoresponsivity and High Photodetectivity for Broadband 365-2240 nm Detection.

The fabrication of graphene/SnS2 van der Waals photodetectors and their photoelectrical properties are systematically investigated. It was found that a dry transferred graphene/SnS2 van der Waals heterostructure had a broadband sensing range from ultraviolet (365 nm) to near-infrared (2.24 μm) and respective improved responsivities and photodetectivities of 7.7 × 103 A/W and 8.9 × 1013 jones at 470 nm and 2 A/W and 1.8 × 1010 jones at 1064 nm. Moreover, positive and negative photoconductance effects were observed when the photodetectors were illuminated by photon sources with energies greater and smaller than the bandgap of SnS2, respectively. The photoresponsivity (R) versus incident power density (P) follows the empirical law R ∝ Pinβ, with β > -1 for positive photoconductance effects and β < -1 for negative photoconductance effects. On the basis of the Fowler-Nordheim tunneling model and a Poisson and drift-diffusion simulation, we show quantitatively that the barrier height and barrier width of the heterostructure photodetector could be controlled by a laser and an external electrical field through a photogating effect generated by carriers trapped at the interface, which could be used to tune the separation and transport of photogenerated carriers. Our results may be useful for the design of high performance van der Waals heterojunction photodetectors.