Metal-semiconductor-metal Photodetectors Research Articles

Responsivity Surge in MAPbI3:PC61BM/Au/ZnO Sandwich‐Structured Photodetector

AbstractThe low gain in the presence of a single transverse external electric field limits the application of metal‐semiconductor‐metal (MSM) photodetectors. Here, a longitudinal built‐in electric field by spin‐coating CH3NH3PbI3:PC61BM on the electrode region of an Au/ZnO MSM photodetector, which constitutes a vertically crossed composite electric field with a transverse external electric field, is constructed. In this case, the transverse electric field collects the electrons, and the longitudinal electric field separates them. Based on this novel electric field structure, carrier multiplication at lower voltage conditions is achieved. Compared to the low voltage, there is a significant amplification effect when the voltage reaches 7 V. The responsivity is increased ≈270 times for UV–vis wavelengths, escalating from ≈0.02 to ≈5.4 A W−1. This study provides a novel carrier transport control scheme for high‐gain perovskite‐based photodetectors.

Improvement of Photoconductivity in a‐Oriented α‐Ga2O3 Thin Films Grown on Sapphire Substrates by Mist Chemical Vapor Deposition

α‐Ga2O3 is a suitable material for UV‐C optical devices owing to its optical absorption edge wavelength. In this study, α‐Ga2O3 thin films are grown on c‐, a‐, m‐, n‐, and r‐oriented sapphire substrates by mist chemical vapor deposition. Furthermore, their structural fluctuations, (normal direction of the surface) and (rotational direction on the surface), are examined. As a result, the a‐oriented α‐Ga2O3 thin films exhibit the smallest and . Based on the results of the previous examination, metal–semiconductor–metal (MSM) photodetectors are fabricated using c‐ and a‐oriented α‐Ga2O3 thin films and their photoconducting properties are characterized. Under D2 lamp light illumination, the MSM photodetector using a‐oriented films produces photocurrent four to six times greater than those using c‐oriented films. The visible‐light rejection ratios are at 10 V and 105.2 at 24 V. The photoresponsivity is estimated to be 2.2 A W−1 under the illumination of a D2 UV lamp and 24 V bias voltage. In these results, it is suggested that the a‐oriented α‐Ga2O3 thin film exhibits a higher in‐plane carrier mobility than the c‐oriented film. Thus, a‐oriented α‐Ga2O3 films are more suitable than c‐oriented α‐Ga2O3 films for fabricating MSM photodetectors.

Substrate temperature dependent crystal structure and deep-ultraviolet photodetection of ZnGa2O4 thin films * *Project supported by This work was supported by the National Natural Science Foundation of China (No. 12074044), the Fund of State Key Laboratory of Information Photonics and Optical Communications (IPOC2021ZT05), and the Fundamental Research Funds for the Central Universities (BUPT, 2023ZCJH1).

Zinc gallate (ZnGa2O4) is a promising material for deep-ultraviolet (DUV) photodetectors, owing to its wide bandgap and high transparency. However, the effect of substrate temperature on the structural and optical properties of ZnGa2O4 thin films prepared by magnetron sputtering is not well understood. Here, we report a systematic study of the influence of substrate temperature on the crystal quality, stoichiometry, bandgap, and photodetection performance of ZnGa2O4 thin films deposited on sapphire substrates. We find that the films undergo a phase transition from amorphous to polycrystalline at 300 °C, and then to single crystalline at 500 °C, accompanied by an increase in the bandgap from 4.6 to 4.9 eV. We also fabricate metal-semiconductor–metal photodetectors based on the ZnGa2O4 thin films with Ti/Au electrodes, which exhibit excellent Ohmic contact and high light-to-dark current ratio. The photodetectors show remarkable and stable DUV response, with the highest performance achieved at a substrate temperature of 650 °C. Our results demonstrate the crucial role of substrate temperature in tailoring the crystal structure and DUV photodetection of ZnGa2O4 thin films, and provide a facile route for optimizing their performance.

Synthesis and characterization of Cu-Doped ZnO nanostructures for UV sensing application

In this work, Fabrication, and characterization of Cu-doped ZnO thin films deposited on porous silicon (PSi) substrates have been reported using electrochemical deposition (ECD) technique. The influence of Cu-doping concentrations on morphology, structure, and electrical characteristics of zinc oxide (ZnO) thin films were presented. X-ray diffraction analysis (XRD) has been used to characterize the lattice constants, average size, in-plane (along a-axis) and out of plane (along c-axis) strains for the Cu–ZnO crystals. The effects of Cu-doping concentration on crystal parameters were also investigated from the XRD analysis. The samples were used for UV-sensing applications. In addition, Cu-doped ZnO and pure ZnO metal–semiconductor-metal photodetector, with Cu as electrode contacts were successfully produced for ultraviolet (UV) detection. The I-V (current–voltage) characteristics were used to study the sensing enhancement. Finally, the UV photodetector based on Cu-doped ZnO films was successfully fabricated and shows a five times enhancement in the sensitivity to UV light compared to that of pure ZnO photodetector.

Gallium oxide cantilevered thin film-based solar-blind photodetector and its arc detection applications

The performance of gallium oxide (Ga<sub>2</sub>O<sub>3</sub>) thin film detector based on metal-semiconductor-metal (MSM) is highly dependent on the uniformity of the Ga<sub>2</sub>O<sub>3</sub> thin film, and the manufacturing process is quite sophisticated, which poses a challenge for the scale-up and mass production of thin film photodetectors. In this work, an MSM Ga<sub>2</sub>O<sub>3</sub> thin film solar-blind photodetector with five-finger interdigital electrodes is fabricated by physically depositing Ga<sub>2</sub>O<sub>3</sub> thin film on the surface of a mass-produced cantilevered thin film chip. Through the microelectromechanical system (MEMS) process, the cantilever electrode structure is prepared, which protects the internal circuit and the integrity of the thin film. The Ga<sub>2</sub>O<sub>3</sub> thin film treated by argon plasma at a low temperature is amorphous, but the photodetector still possesses considerable ultraviolet detection performance. At a bias voltage of 18 V, it approaches the detection performance of crystalline Ga<sub>2</sub>O<sub>3</sub> thin film, with a detectivity of 7.9×10<sup>10</sup> Jones, an external quantum efficiency of 1779%, rise time and decay time of 1.22 s and 0.24 s, respectively. Moreover, a system of arc detection is built in outdoor environments. Without any optical focusing system, this photodetector achieves sensitive detection of pulsed arc in an outdoor sunlight environments. For pulsed arcs with an output voltage of 100 kV, the photodetector is capable of sensitive detection at a distance of 25 cm. Besides, the maximum detection distance of 155 cm indicates that the photodetector will have a favorable potential application value in the field of solar-blind detection. This work develops a sensitive functional thin film deposition technology based on the cantilever electrode structure fabricated by the MEMS process, which avoids the influence of the large-area uniformity of the functional thin film on the etching circuit. It provides a new technical approach and process route for preparing MSM photodetectors.

High performance metal-semiconductor-metal ultraviolet photodetector based on mixed-dimensional TiO2/CsPbBr3 heterostructures

Zero-dimensional (0D) and one-dimensional (1D) mixed heterostructure semiconductors can bring superior electrical and optoelectronic performances due to the synergistic advantages of different dimensionalities. Here, a metal-semiconductor–metal (MSM) ultraviolet (UV) photodetector based on 1D-0D TiO2/CsPbBr3 heterostructure semiconductor is constructed, which exhibits excellent photodetection performance. A back-to-back Schottky contact is formed in the MSM (Au/TiO2/Au) structure due to the large band-energy bending resulted from the abundant surface-states at 1D-TiO2 surface. Under an applied voltage, a small saturation current flows through the device. Benefiting from the decoration of CsPbBr3 QDs, the dark current of MSM photodetectors can be further suppressed, and producing the improved on/off ratio (I light/I dark), photoresponsivity (R λ ), and detectivity (D*). PL properties study suggested that an energy transfer is occurred between the 0D-CsPbBr3 and 1D-TiO2. The TiO2/CsPbBr3 heterojunctions are beneficial for photo-induced charge transfer in hetero-interface because of the type-II energy-band alignment, but not non-radiative energy transfer from 0D-CsPbBr3 to 1D-TiO2. On the whole, this study depicts a fascinating coupling architecture of mixed-dimensional materials toward implementing low-cost and high-performance optoelectronic devices.

(Invited) Leading-Edge Diamond FET, MEMS, and Photodetector Devices

Diamond is a candidate material for next-generation power electronics, micro-electro mechanical systems (MEMS), and solar-blind deep-ultraviolet (DUV) photodetector devices with excellent thermal stability and radiation hardness, which operate under extreme environment. In order to use an advantage of high-density hole channel of hydrogenated diamond (H-diamond) surface, we have developed the high-k stack gate dielectrics and AlN heterojuction gate for H-diamond FETs, such as HfO2/HfO2, LaAlO3/Al2O3 Ta2O5/Al2O3, and ZrO2/Al2O3, AlN/Al2O3 prepared by a combination of sputter-deposition (SD) and atomic layer deposition (ALD) techniques [1,2]. We also demonstrated the artificial diamond Fin-FETs with high-current level [3] and the nanolaminate insulator gate metal-oxide-gate FETs (MOSFETs) with k value as high as 100 [4], and the new transistor concept named by metal-insulator-metal-semiconductor field-effect transistor (MIMS-FET) to achieve normally-off operation by combining the advantages of MOSFET and metal-semiconductor FET [5]. In addition, we developed the routine ion-implantation process for preparing the diamond cantilever with a resonant frequency quality factor as high as one million [6,7]. We have also developed thermally stable Schottky barrier photodiode (SPD), metal-semiconductor-metal photodetector (MSMPD), and MSM-type SPD (IDF-SPD) with a large photoconductivity gain in DUV wavelength and a large discrimination ratio between DUV/visible light responsivity [8,9]. In this presentation, we will review the comprehensive our work on the diamond FET, MEMS, and photodetector devices. Acknowledgements: This work was in collaboration with J-W. Liu, M. Imura, M-Y. Liao, J. Alvarez in NIMS and A. Ouchiero and E. Obaldia in University of Taxes, Dallas, and partly supported by JSPS KAKENHI Grant Number 20H00313.

InGaAs-Based MSM Photodetector: Researching Absorption Layer, Barrier Layer, and Digital Graded Superlattice Layer with 3D Simulation

The effects of absorption, barrier, and digital graded layer thickness on dark current and photocurrent in Metal Semiconductor Metal (MSM) photodetectors by using 3D Silvaco TCAD are reported. The photo-dark current ratio (Iphoto/Idark) is calculated using the photocurrent and dark current values obtained by simulation. In study A (absorption layer thickness variation) the photocurrent, dark current and photo-dark current ratio are increased with increased absorption layer thickness, and the dark current is 1.138x10-7 A levels. In Study B (barrier layer thickness variation), when the barrier layer is added to the absorption layer, the dark current is decreased to 1.56x10-11 A levels. It is reported that the photo-dark current ratio with increasing barrier layer thickness increases. In study C (digital graded superlattice layer thickness variation), the dark current increases, and photocurrent decreases with the increase of the digital graded superlattice layer thickness. However, the photo-dark current ratio with increasing digital graded superlattice layer thickness decreases. Furthermore, a similar trend of development is observed on photo-dark current with adding of the barrier layer and digital graded superlattice layer on the absorption layer. These findings demonstrate the importance of optimizing layer thickness in MSM photodetectors for improved device performance.

Photocarrier transport reconstruction and dramatical performance enhancement in ultrawide-bandgap ε-Ga2O3 photodetectors via surface defect passivation

The semiconductor surface is a major platform dictating carrier transport and recombination, in particular for planar photoconductive devices such as metal-semiconductor-metal (MSM) photodetectors. Here we demonstrate the integration of an ultrathin Al2O3 capping layer to effectively passivate the surface defects of epitaxial ε-Ga2O3 films and substantially enhance the photodetector performance. Incorporating an Al2O3 layer is found to significantly reduce the dark current of ε-Ga2O3 MSM photodetectors by more than three orders of magnitude, and simultaneously enhance the photocurrent and the response speed. With an ultrathin Al2O3 surface layer, the Al2O3/ε-Ga2O3 MSM photodetector achieves a superhigh responsivity of >104 A/W, a detectivity of >1016 Jones with a photo-to-dark ratio of >107, an UV–vis rejection ratio of >104 and millisecond response time for continuous-wave illumination. The surface passivation mechanism is analyzed by combined X-ray photoemission spectroscopy, secondary ion mass-spectroscopy and numerical calculations. It is revealed that the Al2O3 capping layer passivates the surface defects that are in the form of reduced tin species and oxygen vacancies, and reconstructs a faster surface transport channel for more efficient photocarrier collection. This study expands the design concept of surface passivation with ultrawide bandgap semiconductors for developing efficient deep ultraviolet photodetectors.

Study of nanoscale three dimensional Au/GaN Schottky junctions: Fabrication, morphology and optoelectronic properties

Owing to the effective carrier transfer at interface, the utilization of three-dimensional (3D) Schottky junctions transcends the limitations imposed by planar junctions, exhibiting significant potentials in optoelectronics of plasmon-semiconductor system. However, in nanoscale, widespread adoption of 3D Schottky junctions are significantly hindered by complexities of nanoscale photolithography processes. In this work, the Au/GaN 3D Schottky junctions are fabricated via thermal induced etching process. The etching behavior is investigated in terms of morphology and optical properties. Based 3D Schottky junctions, GaN metal–semiconductor-metal photodetectors are fabricated and the optoelectronic properties of Au/GaN 3D Schottky barriers are investigated. With 3D Schottky junctions, the sensitivity and detectivity have been improved by 20.7 and 3.6 times in comparison with the planar Au/GaN junctions. Meanwhile, the noise equivalent power has been reduced of 76.3%, showing a large improvement in response of small signals.

Metal–Semiconductor–Metal Ultraviolet Photodetectors Based on Al Nanoparticles in 4H-SiC Microholes

A significant ultraviolet (UV) detection enhancement is realized by etching microhole (MH) arrays and localized surface plasmon resonance (LSPR) of Al nanoparticles (NPs) on 4H-SiC metal–semiconductor–metal (MSM) photodetectors (PDs). 4H-SiC PDs with different diameters of MHs are fabricated, which exhibit an ultralow dark current of approximately 5.0 × 10–15 A at 5 V bias. The PD with 3 μm MH exhibits the best performance, and its peak responsivity is 35% higher than that of device without MH. The peak responsivity of PDs with both 3 μm MH and NPs enhanced nearly 6 times that without Al NPs. The PD with both 3 μm MH and Al NPs indicates the best detection performance, with a maximum detectivity of 4.0 × 1013 Jones at 270 nm, which is nearly an order of magnitude higher than devices without Al NPs. The fabricated MH and Al NPs MSM PDs have a high response on the order of nanoseconds, with a rise/decay time of 2.1 ns/2.5 ns at 5 V bias. The complementary optical properties of MH and Al NPs with 4H-SiC can promote the development and application of high-performance UV PDs.

Study of Porous III-V Surface Structure via Etching Process: Effect of Pore Depth

In this project, the surface structure of III-V semiconductor, GaAs, was altered to enhance the optical and electronic properties of the semiconductor. This project involved the designing and fabrication of non-porous and porous GaAs structures using SILVACO TCAD tools. The porous GaAs with different pore depth were designed and simulated to investigate the effect of pore depth on the optical and electrical properties of GaAs semiconductor. The pore depth of porous GaAs structure was varied with 2, 4, 6 and 8 μm. The porous GaAs structures were then tested for the metal-semiconductor-metal (MSM) photodetector device application. The non-porous and porous GaAs MSM photodetectors were compared systematically through current-voltage (I-V) characteristics, current gain, and spectral response. The result showed that the porous GaAs MSM photodetector has better performance in terms of electrical and optical properties than the non-porous photodetector. Amongst the MSM GaAs photodetectors, the porous GaAs photodetector with pore depth of 6 μm obtained the highest current gain value of 3.22. While for optical properties, the spectral response showed the current intensity of 11.370 µA which was recorded at the peak wavelength of 880 nm. Therefore, porous GaAs showed good potential and can be used for optoelectronic device applications such as MSM photodetector.

Preparation of hierarchical MOF-5 films using morphology controlled ZnO coatings for temperature dependent optical sensors application

Morphology and well-organized hierarchical structures are so effective on the properties of materials and their device applications. Herein, the metal organic framework (MOF-5) has been prepared by solvothermal transformation of nanostructured zinc oxides (ZnO) with different morphologies including nanorods (NRs), hollow spheres (HSs) and porous spheres (PSs). The SEM image indicates growth of MOF-5 sheets around the ZnO NRs with straight hexagonal arrangement. X-ray diffraction (XRD) illustrates the good crystal structure of MOF-5 grown around the ZnO NRs with a dominant crystal orientation (220). Moreover, the morphology and crystalline properties of the ZnO NRs remained intact after the deposition of MOF-5 structures. The photoluminescence (PL) properties of the MOF-5/ZnO film show a slight improvement compared to both the ZnO and MOF-5 components, which must originate from the improved transfer of charge carriers between the MOF-5 and ZnO NRs. The sensitivity and detectivity 5.6 and 1.2 times increased by decreasing temperature from 300 K to 285 K. Finally, a metal-semiconductor-metal (MSM) photodetector based on MOF-5/ZnO NRs was prepared. The optoelectrical behavior of the device is determined through current-voltage (I–V) and time-volage (t-V) curves under UV illumination at different temperatures. The MOF-5/ZnO MSM photodetectors are a temperature-dependent photodetector with excellent UV photosensitivity at lower temperatures. The voltage responsivity was 43.64 and 70.73 kV W−1 at 300 K and 285 K, respectively. NEP and detectivity was measured 15.53 pW Hz−1/2 and 2.03 × 108 Hz−1/2w−1 at 285K respectively.

Enhancing Photoresponse of GaAs-Based Photodetector by Plasmon Grating Structures

Nanostructured metal–semiconductor-metal photodetectors (MSM-PDs) can assist in future high-speed communication devices for achieving high responsivity characteristics. However, such devices suffer from low responsivity due to low absorption, and the large band gap limits its detection range. Herein, we propose a GaAs-based photodetector with enhanced photoresponse by plasmonic Au-GaAs grating structure. The design of a grating structure on the surface of n-GaAs can excite a plasmon mode to enhance the photoelectric performance of photodetectors. Consequently, under 795 nm incident light irradiation, the grating hybrid detector exhibits a nearly 4.2-fold increase in photocurrent compared to the bare GaAs device. The enhanced absorption can be up to 99% and a specific responsivity of 240 mA/W is realized. These results can thus provide a potential scheme to fabricate high-performance GaAs detector for numerous applications.

Fabrication of UV Photodetectors Based on Photoelectrochemically Etched Nanoporous Silicon: Effect of Etchants Ratio

Despite several attempts to enhance the electrical and charge carrier transport characteristics of porous silicon (PSi), the requisite conditions for optimally synthesizing n-PSi with appealing optoelectronic properties are yet to be achieved. Therefore, this research explores the effect of the chemical ratio of precursor materials (HF:C2H6O:H2O2) on the surface morphology, crystalline structure, and optical and electric properties of PSi. The PSi was produced by photoelectrochemical etching followed by anodization of the n-type Si under light illumination. The properties of the as-prepared PSi were studied by means of microscopic and spectroscopic techniques. The HF:C2H6O:H2O2 chemical ratio was optimized at 2 : 1 : 1. A metal–semiconductor–metal (MSM) ultraviolet photodetector (Pt/n-PSi/Pt) was fabricated, which exhibited high performances under UV light (365 nm) illumination. The photodetector was shown to be highly stable and reliable with a rapid rise time of 0.56 s at a bias voltage of +5 V. The MSM photodetector displayed responsivity (Rp) of 9.17 A/m at 365 nm, which significantly exceeds the values reported for TiC/porous Si/Si in some contemporary research. The photodetector fabricated from n-PSi, synthesized at an optimum chemical ratio (2 : 1 : 1) exhibited the best photodetection performance, possibly due to the high porosity and defect-free state of the n-PSi thin films.

Vertical asymmetric metal-semiconductor-metal photodiode based on β-Ga2O3 thin films fabricated via solution process for arc discharge detection

Arc discharge detection is a preeminent strategy for diagnosing aging of high-power electric equipment. Therefore, the timely detection of arc discharge can prevent immense disasters, such as massive fire accidents. Ultraviolet C (UVC) photodetectors (PD) are effective devices for optical arc discharge detection because of their solar blindness, which enables noise-free and highly selective arc discharge detection. In this study, we developed a solution-processed β-Ga2O3-based vertical asymmetric metal-semiconductor-metal (MSM) UVC PD as a high-performance and inexpensive UVC detector. The high bandgap of photoactive β-Ga2O3 (4.7–5.1 eV) enables selective UVC detection. The Schottky barrier heights at two different metal-semiconductor junctions (PEDOT:PSS/β-Ga2O3 and ITO/β-Ga2O3) were systematically modulated by varying the β-Ga2O3 film annealing temperature and thickness, which enabled fast photoresponse and self-powered operation, as demonstrated by various optical and electrical analyses. The optimized device exhibited a fast photoresponse (rise/fall time of 67/53 ms) and high responsivity (41 mA W−1) and detectivity (1.5×1011 Jones) in self-powered mode. The instantaneous arc discharge was successfully detected using the β-Ga2O3 based vertical MSM PD, demonstrating its feasibility for arc discharge detection. Thus, this study provides new insights into inexpensive self-powered PDs that can be implemented for the facile and prompt monitoring of aging electric equipment and prevention of potential fire accidents.

High-performance fully transparent Ga2O3 solar-blind UV photodetector with the embedded indium–tin–oxide electrodes

Transparent ultraviolet (UV) photodetectors have attracted the increasing attention due to their giant potential in integrated transparent electronics applications. In this work, a fully transparent metal-semiconductor-metal (MSM) solar-blind UV photodetector with embedded indium–tin–oxide (ITO) electrodes based on Ga2O3 films was successfully designed and constructed for the first time. A novel method to prepare a MSM photodetector with embedded electrode structure is proposed by selective epitaxying β-Ga2O3 thin films on c-plane sapphire substrate with ITO inter-digital electrodes prepared in advance. An ultra-low dark current of 1.6 pA, a superb UV-to-visible rejection ratio of 1.3 × 106 (R250/R400), a high specific detectivity of 7.4 × 1015 Jones and a large responsivity of 74.9 A/W can be observed in our device at 10 V, which are superior to those of other reported transparent UV photodetectors based on Ga2O3 films. The strong and uniform electrical field in β-Ga2O3 between two adjacent embedded ITO electrodes, and the high quality of β-Ga2O3 films should be responsible the excellent solar-blind photodetection performance. Our findings pave a new way to realize a high-performance fully transparent Ga2O3 solar-blind UV photodetector, which has the giant potential for applications in future transparent electronics.

Air-Stable Flexible Photodetector Based on MXene-Cs3Bi2I9 Microplate Schottky Junctions for Weak-Light Detection.

Weak-light detection technology is widely used in various fields, including industry, high-energy physics, precision analysis, and reflection imaging. Metal-semiconductor-metal (MSM) photodetectors demonstrate high detectivity and high response speed and are one of the suitable structures for the preparation of weak-light detectors. However, traditional MSM photodetectors tend to exhibit high dark currents, which are not conducive to performance improvement. Here, a MXene-Cs3Bi2I9-MXene weak-light detector is proposed. Based on the MXene-Cs3Bi2I9 Schottky junctions, the dark current is reduced by 2 orders of magnitude and the responsivity is significantly improved compared with the traditional Cr/Au-Cs3Bi2I9-Cr/Au MSM photodetector. The device demonstrates excellent photodetection capacity with a photoresponsivity of 6.45 A W-1, a specific detectivity of 9.45 × 1011 Jones, and a fast response speed of 0.27/2.32 ms. Especially, the device yielded a superior weak-light detectable limit of 10.66 nW cm-2 and demonstrated excellent optical communication capability. Moreover, such a flexible device shows little degradation in photodetection performance after extreme bending for 4500 cycles, proving remarkable bending endurance and flexibility. The obtained results highlight the great potential of such Cs3Bi2I9/MXene devices as a stable and environmentally friendly candidate for weak-light detection.

Directional Carrier Transport in Micrometer-Thick Gallium Oxide Films for High-Performance Deep-Ultraviolet Photodetection.

Incorporating emerging ultrawide bandgap semiconductors with a metal-semiconductor-metal (MSM) architecture is highly desired for deep-ultraviolet (DUV) photodetection. However, synthesis-induced defects in semiconductors complicate the rational design of MSM DUV photodetectors due to their dual role as carrier donors and trap centers, leading to a commonly observed trade-off between responsivity and response time. Here, we demonstrate a simultaneous improvement of these two parameters in ε-Ga2O3 MSM photodetectors by establishing a low-defect diffusion barrier for directional carrier transport. Specifically, using a micrometer thickness far exceeding its effective light absorption depth, the ε-Ga2O3 MSM photodetector achieves over 18-fold enhancement of responsivity and simultaneous reduction of the response time, which exhibits a state-of-the-art photo-to-dark current ratio near 108, a superior responsivity of >1300 A/W, an ultrahigh detectivity of >1016 Jones, and a decay time of 123 ms. Combined depth-profile spectroscopic and microscopic analysis reveals the existence of a broad defective region near the lattice-mismatched interface followed by a more defect-free dark region, while the latter one serves as a diffusion barrier to assist frontward carrier transport for substantially enhancing the photodetector performance. This work reveals the critical role of the semiconductor defect profile in tuning carrier transport for fabricating high-performance MSM DUV photodetectors.

Toward sustainable optoelectronics: solution-processed quantum dot photodetector fabrication using a surgical blade

Fabrication of optoelectronic devices relies on expensive, energy-consuming conventional tools including chemical vapor deposition, lithography, and metal evaporation. Furthermore, the films used in these devices are usually deposited at elevated temperatures (>300 ° C) and under high vacuum, which necessitate further restrictions on the device fabrication. Developing an alternative technology would contribute to the efforts on achieving a sustainable optoelectronics technology. Keeping this in our focus, here we present a simple technique to fabricate visible photodetectors (PDs). These fully solution-processed and transparent metal-semiconductor-metal (MSM) PDs employ silver nanowires (Ag NW) as the transparent electrodes replacing the indium-tin-oxide (ITO) commonly used in optoelectronic devices. By repeatedly spin coating Ag NWs on a glass substrate followed by the coating of zinc oxide nanoparticles, we obtained a highly conductive transparent electrode reaching a sheet resistance of 95 Ω / □ as measured by the four-probe method. Optical spectroscopy revealed that the transmittance of the Ag NW-ZnO films was 84% at 450 nm while the transmittance of the ITO films was 90% at the same wavelength. Following the formation of the conductive film, we scratched it using a heated surgical blade to open a gap. The scanning electron microscope images indicate that a gap of ∼30 μm is opened forming an insulating line. As the active layer, we drop-casted red-emitting CdSe/ZnS core-shell quantum dots (QDs) onto this gap to form a MSM PD. These visible QD-based PDs exhibited responsivities and detectivities up to 8.5 mA / W and 0.95 × 109 Jones, respectively at a bias voltage of 5 V and wavelength of 650 nm. These proof-of-concept PDs show that the environmentally friendly, low-cost, and energy-saving technique presented here can be an alternative to conventional, high-cost, and energy-hungry techniques while fabricating photoconductive devices.