Metal-semiconductor Structures Research Articles

Huge photosensitivity gain combined with long photocurrent decay times in various polymorphs of Ga2O3: effects of carriers trapping with deep centers

Abstract The materials system of ultra-wide bandgap Ga2O3 has already shown great promise in the field of solar-blind photodetectors with high photoresponsivity, high photoresponsivity gain and low dark current. These promising results have been achieved on Ga2O3 films of different polymorphs and by different methods, often not with particularly high crystalline quality. In fact, it would often seem the case that the lower the crystalline quality of the films, the higher the photosensitivity and its gain. This, however, is in most cases accompanied by unusually long photocurrent build-up and decay times. We show that the experimental results can be explained by models in which the high photosensitivity gain is related to the effects of holes being trapped by deep states that, in Schottky diodes, results in the decrease of the Schottky barrier height with consequent increase of electron current, and in Metal-Semiconductor-Metal (MSM) structures additionally gives rise to the usual gain increase due to the increased concentration and lifetime of electrons. We present and discuss the models describing the effects in Ga2O3 Schottky diodes, MSM structures, unipolar and bipolar heterojunctions and propose possible candidates for the role of the hole traps in different Ga2O3 polymorphs. We also discuss the existing results for the photocurrent build-up and decay times and offer possible explainations of the observed temperature dependences of the characteristic times where such data are present.

High ultraviolet gain in Ga2O3/ZnO heterojunction photodetector based on MSM structure

Amorphous Ga2O3 (a-Ga2O3) has attracted extensive attention due to its simple preparation process and low cost, but the extension of photoelectron lifetime caused by the trap state inhibits the responsiveness of a-Ga2O3 photodetector (PD), and how to improve the ultraviolet (UV) gain of a-Ga2O3 based PD is still a challenge. In this study, an a-Ga2O3/ZnO heterojunction PD based on metal-semiconductor-metal (MSM) structure was designed and fabricated by radio frequency magnetron sputtering (RFMS), and a high-concentration electron transport channel was formed by using carrier multiplication and specific band structure in the high-field region of MSM structure, which achieved high optical gain and extraordinary optical detection ability. In the UVC-UVA band, the device has a peak responsivity of 1.59 A W−1 and a high light-dark ratio, EQE and D* of 1×104, 647 % and 3.6×1012 Jones under 5 V, respectively. In particular, compared to ZnO PD and a-Ga2O3 PD, the responsivity of the device is improved by a factor of 21 and 90, respectively. This study provides a new and effective method for the significant improvement of a-Ga2O3 based UV photoelectric detection performance.

Characterization of composition dependence of properties of a MgNiO-based MSM structure

In this study, the effect of Mg composition on structural and optical properties of MgxNi1-xO alloy thin film single crystal semiconductors as well as their implementation into Metal-Semiconductor–Metal (MSM) photodetector are studied. An 850 meV blue-shift of the bandgap is observed from 3.65 eV to 4.50 eV with increasing Mg composition from 0% to 67%. The deep ultraviolet/visible rejection ratio, which is the ratio of photosensitivity at a peak wavelength of 360 nm to that at 450 nm is found to be ∼58 for Mg composition of 67%. Mg rich (%67 Mg) alloy-based photodetector is found to have two orders smaller dark current and have higher spectral response compared to NiO-based one. Spectral responsivities for MgxNi1-xO photodetectors are determined as 415 mA W−1, 80 mA W−1, and 5.6 mA W−1 for Mg compositions of 67%, 21%, and 0% (reference-NiO), respectively. Furthermore, the detectivity of the photodetectors enhances as Mg composition increases and the highest detectivity of a magnitude of ∼1011 Jones is found for the photodetector with Mg composition of 67%.

Heteroepitaxial α‐Ga2O3 Thin Film‐Based X‐Ray Detector with Metal–Semiconductor–Metal Structure

This study explores the potential of 700‐nm‐thick heteroepitaxial α‐Ga2O3 thin films on c‐plane sapphire substrates for X‐ray detector applications. The crystal quality and optical bandgap of the heteroepitaxial α‐Ga2O3 thin films are comparable to those of high‐quality α‐Ga2O3 thin films. The α‐Ga2O3 thin film X‐ray detector with a metal–semiconductor–metal structure exhibits a charge neutral point shift, resulting in a short‐circuit current density of 9.07 nA cm−2 and an open‐circuit voltage of –1.2 V. The detector achieves the highest signal‐to‐noise ratio of 973 at 0 V, while the maximum sensitivity (14.7 μC Gyair−1 cm−2) occurs at 10 V. The proposed X‐ray detector demonstrates a reliable transient response and long‐term robustness, suggesting the promise of heteroepitaxial α‐Ga2O3 for low‐cost, high‐quality, large‐area X‐ray detectors.

Modulation of oxygen vacancies in InSnZnO thin films and applications for high-speed metal-semiconductor-metal ultraviolet photodetectors

Enhancing the response speed of photodetectors is of great significance, for meeting the requirements of high-density optical arrays and integration. Wide bandgap indium oxide with high electron mobility makes it suitable for the preparation of high-speed response ultraviolet photodetectors. Nevertheless, oxide semiconductor is prone to form oxygen vacancies during the growth process, leading to persistent photoconductivity in photodetectors, which considerably limits the practical application in ultraviolet detection. In this work, a well-performing metal–semiconductor-metal structure ultraviolet photodetector based on amorphous indium-tin-zinc-oxide was fabricated via co-sputtering technique. By enhancing the oxygen ratio during the co-sputtering, the concentration of oxygen vacancies was effectively reduced, which modulated the performances of the photodetector. This approach not only shortened the photodetector’s response time but also omitted the annealing step, enabling a room-temperature fabrication process. As a result, the optimized indium-tin-zinc-oxide photodetector of 30 % oxygen exhibited remarkably rapid response characteristics under 367 nm ultraviolet irradiation, with rise and decay times of 0.018 and 0.066 s, respectively. Simultaneously, the optimized indium-tin-zinc-oxide phototransistor exhibited exceptional performance metrics, including a high photoresponsivity of 480 A/W, a detectivity of 3.2 × 1012 Jones and an external quantum efficiency of 1336 % under 367 nm ultraviolet irradiation with 1 mW/cm2 light intensity.

Electrical and dielectric behaviors of Al/SiO2-surfactant/n-Si schottky structure in wide range of voltage and frequency

SiO2 surfactant insulator into Al/n-Si metal-semiconductor (MS) structure was fabricated into Al/SiO2-surfactant/n-Si metal–insulator–semiconductor (MIS) structure and its effect on the electrical properties of the final structure was investigated. The SiO2-surfactant layer is coated on the n-Si wafer by the spin coating technique. The I-V data is used to calculate the fundamental electrical parameters of this MIS structure. The density distribution of the surface states (Nss) is computed depending on the energy at forward potential. The current conduction mechanisms (CCMs) in the MIS structure are examined at the reverse and forward biases applied. To get more accurate and reliable results, the profiles of I-V and C/(G/ω)-V are measured at a wide range of bias voltage (0.25V-4V) and frequency (1kHz-1MHz), respectively. The performance of the MIS is significant due to the basic values of electrical parameters (n, I0, Rs, Rsh, Nss, ΦB0, and Rectifying Ration (RR)) and dielectric parameters (ε′, ε″, tan δ, M′, M″, Rs, and σ) compared with the MS structure. The other electrical parameters (ND, WD, Em, ΦΒ) are extracted from the slope and intercept of the reverse bias C−2-V plot as a function of frequency. Furthermore, the profile of voltage-dependent Rs and Nss was determined using different methods from I-V and C/G-V data and examined comparatively with each other. The changes in impedance properties with frequency and voltage of the MIS are discussed in detail.

Self-Powered InGaZnO Ozone Gas Sensors Based on a Metal–Semiconductor–Metal Structure with Asymmetric Interdigitated Electrodes

Self-Powered InGaZnO Ozone Gas Sensors Based on a Metal–Semiconductor–Metal Structure with Asymmetric Interdigitated Electrodes

Enhanced sensitivity of MoS2:Er-based flexible near-infrared photodetectors via tellurium-induced interfacial charge transfer

The persistent photoconductive behavior caused by traps in the active materials usually weakens the sensitivity and stability of photodetectors. Herein, tellurium (Te) microwire and polyvinyl alcohol (PVA) composites were developed as functional flexible substrates to improve the near-infrared (NIR) photoresponse performance of MoS2:Er-based devices with the metal–semiconductor–metal structure. The flexible photodetector exhibits a rise/fall time of ∼2.9–3.1 ms, a responsivity of ∼0.28 mA W−1, and a detectivity of ∼1.41 × 1010 Jones under 808 nm irradiation. The enhanced mechanism can be attributed to the charge transfer between Te microwires and MoS2:Er films, which suppresses the dark current of the device and optimizes the generation process of electron–hole pairs under light illumination. Meanwhile, the flexibility of the device allows it to be employed in human heart rate monitoring. This work offers a simple and essential strategy for constructing integrated flexible NIR photodetectors with high performance.

Efficient and stable self-powered PbSe photodetectors via doping-induced asymmetric Cr electrodes modulation of surface work function

Conventional PbSe infrared photodetectors typically demands a substantial external electric field, posing challenges in energy-constrained environments. Self-powered photodetectors present a promising avenue for addressing such electricity-related challenges. Nevertheless, the inherent limitations of symmetric Schottky contacts in metal-semiconductor-metal (MSM) photodetectors constrain their self-powered performance, resulting in opposing photocurrents. Constructing asymmetric MSM structures usually requires intricate design or sustained external fields. In this study, we propose a novel contact engineering strategy based on iodine doping to modulate surface work functions of PbSe film. Utilizing Cr electrodes, we achieve Ohmic contact on the iodine-doped top surface of PbSe film and Schottky contact on the as-grown bottom surface. This approach establishes a self-powered PbSe infrared photodetector with an asymmetric top-bottom MSM structure. We comprehensively investigate contact engineering by investigating surface chemical states, elemental variations, and surface work functions variation. Remarkably, the photodetector demonstrates an exceptional zero-bias detectivity of 1.13 × 109 Jones, with an extremely low dark current of 3.67 pA, high Ilight/Idark ratio exceeding 104, and extremely short response times of less than 1 ms, respectively. Our work introduces a new strategy for modifying the band structure, contributing to the fabrication of high-performance self-powered photodetectors.

Electrical properties of PVC:BN nanocomposite as interfacial layer in metal-semiconductor structure

In this study, a comprehensive examination is assumed to investigate the influence of interfacial layers composed of polyvinyl chloride (PVC) and polyvinyl chloride-boron nitride (PVC: BN) on the electrical characteristics of the Au/n-Si structure. Two distinct structures, namely Au/PVC/n-Si (MPS1) and Au/PVC: BN/n-Si (MPS2), are fabricated for this purpose. The provided boron nitride (BN) nanostructures are analyzed using X-ray diffraction (XRD) patterns to determine their average crystalline size and surface morphology. Following the structural analysis, current-voltage (I–V) measurements are conducted over an extensive voltage range (± 3 V). Subsequently, the fundamental electrical properties of the developed Schottky structures are determined using various methods and compared. Experimental results indicate that the PVC: BN nanocomposite leads to an increase in the potential barrier height (BH), shunt resistance (Rsh), and rectifying rate (RR = IF/IR), while simultaneously decreasing the ideality factor (n), series resistance (Rs), and surface states density (Nss). It was discovered that the MS structure’s RR was 7 times lower than that of the MPS2 structure. Moreover, the energy-dependent Nss density is also derived using n(V) and ΦB0(V) functions. Based on the ln(IR)−VR0.5 profile at the reverse bias region, the Schottky-emission (SE) type conduction mechanism is effective for MS structures, whereas Poole-Frenkel-emission (PFE) is effective for MPS structures.

Development of Cu2O-Cu-ZnO ternary nanocomposites for high-performance photoelectrochemical non-enzymatic glucose sensor

The construction of ternary nanocomposites has shown promising prospects in photoelectrochemical (PEC) glucose sensing. In this work, cubic Cu2O-Cu-ZnO (CCZ) ternary nanocomposite was synthesized through a straightforward method. The CCZ/Nafion/GCE (glassy carbon electrode) electrode possessed excellent photo-response and was used for PEC glucose sensing. As the light intensity increased, the CCZ/Nafion/GCE electrode exhibited higher sensitivity (1.213 mA mM−1 cm−2), wider linear range (0–5 mM), shorter response time (3 s) and lower detection limit (2.10 μM). The anti-interference and stability tests proved the high stability of the CCZ-based glucose sensor. Further results confirmed that the glucose concentration detected by the CCZ-based glucose sensor was close to the results detected by a commercial sensor, indicating the application prospect of the CCZ-based PEC glucose sensor. This work provided a novel perspective for the development of ternary semiconductor-metal structure in PEC glucose sensing.

Room temperature growth of CsPbBr3 single crystal for asymmetric MSM structure photodetector

UV–visible broadband light harvesting ability is critical for photodetectors, and all inorganic perovskite CsPbBr3 is regarded as a promising candidate as the response active material. Herein, a saturated-solution crystallization method is employed to synthesize CsPbBr3 single crystal. Temperature-dependent photoluminescence spectra with one-photon and two-photon excitation are systematically investigated, determining a large exciton binding energy of 39.8 meV. This allows the stable excitonic emission of CsPbBr3 single crystal at room temperature. Subsequently, an asymmetric structure CsPbBr3 photodetector is fabricated by using InGa alloy as the Ohmic electrode and Au as the Schottky electrode. At -8 V, the device exhibits a prominent response to the irradiation from UV to green band with a maximum responsivity of 2.56 A/W, an external quantum efficiency of 580 %, and a detectivity of 1.24 × 1013 Hz1/2 W−1. In addition, the CsPbBr3 photodetector also presents rapid response speeds at both reverse and forward bias voltages and self-powered characteristics owing to the Schottky depletion layer underneath the Au electrode. The demonstration of asymmetric metal-semiconductor-metal (MSM) structure photodetector presents a promising pathway toward next-generation CsPbBr3 optoelectronic devices.

Optoelectric response of Schottky photodiode with a PVP: ZnTiO3 nanocomposite as an interfacial layer

This work aims to study the photo-response of the fabricated silicon-based Al/PVP:ZnTiO3/p-Si photodiode (PD) in a wide range of illumination intensities. To make a metal-polymer/nanocomposite-semiconductor (MPS) PD, a thin film of PVP:ZnTiO3 nanocomposite is deposited at the interface of the metal-semiconductor (MS) structure. Information regarding the preparation and manufacturing procedures is provided. Through the examination of the current-voltage (I–V) behavior, essential electrical properties such as leakage current (I0), barrier height (ΦB0), ideality factor (n), series and shunt resistances (Rs, Rsh), energy-dependent interface states density (Nss), photocurrent (Iph), and photosensitivity (S) are acquired. The thermionic emission (TE) theory, along with the Norde and Cheung methods, is employed to calculate the parameters ΦB0, n, and Rs. The values of ΦB0 and Rs are decreased by raising the illumination intensity while the n value is increased. In addition, the illumination coefficient (α) and the value of ΦB0 in the ideal case are determined from the ΦB0-P and ΦB0-n plots. The efficiency (η) of the sample is calculated at each illumination intensity whose maximum value is 2.30 % at the intensity of 450 mW/cm2. The illumination-dependent photocurrent is investigated at the negative bias region that shows a good linear behavior in the ln(Iph)-ln(P) profile. The photosensitivity (S) of the fabricated PD is obtained as ⁓500 which is, compared with previous PDs. These findings demonstrate that the developed silicon-based MPS-type PD with a structure of Al/PVP:ZnTiO3/p-Si exhibits a good photo-response and can successfully replace traditional MS PDs in optoelectronic and photovoltaic applications.

Investigation of electrical, dielectric and interface state densities of Al/p-Si structures with PTCDA interlayer under different light intensities

In our study; we investigated illumination intensity-dependent electrical and dielectric properties of the Al/p-type Si metal-semiconductor (MS) structures with perylenetetracarboxylic dianhydride (PTCDA) interface using current-voltage (I–V) and capacitance-conductance-voltage (C-G/ω--V) measurements. Thin film layer with PTCDA interface was coated on p-type Si by Spin Coating method. The structure of PTCDA organic semiconductor powder examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrical parameters such as ideality factors (n), barrier heights (Φbo), rectification ratios (RR), saturation currents (I0) and series resistances (RS) were obtained from both thermionic emission (TE) theory and Cheng theory and compared with each other. Dielectric properties such as dielectric constant (ε′), dielectric loss (ε''), loss tangent (tanδ), electrical conductivity (σac), and interface state densities (NSS) were obtained from C–V and G/ω-V measurements. It was seen that the values of ε′, ε'', tanδ, and NSS decreases with increasing illumination while σac increase with increasing illumination intensity. Experimental results show that Al/PTCDA/p-type Si semiconductor structure can improve efficiency in electronic devices.

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.

Experimental and theoretical analysis of a Visible-Light photodetector based on cadmium sulfide fabricated on interdigitated electrodes

The wide range of applications for photodetectors, such as in space, industry, medical, and military, has garnered significant research attention in recent years. In this study, an n-type single-layer photodetector based on a Cu/CdS/Cu metal–semiconductor-metal structure with a micro interdigitated electrode array (IDE) was fabricated. The surface morphology and absorption properties of the CdS thin films were characterized using atomic force microscopy, scanning electron microscopy, and UV–Vis spectrometry. The photo response characteristics of the photodetector were recorded across wavelengths of 400–780 nm. The optoelectronic analyses of the structure revealed a maximum responsivity value of approximately 98.73 % at 405 nm incident light, with a high response time of about 0.12 s. Furthermore, the structure was theoretically studied and simulated, with the simulation results demonstrating good agreement with the measured experimental evidence. The above results indicate that the present CdS photodetector holds excellent potential for use in high-sensitivity optoelectronic integrated circuits.

Exploration of a wide bandgap semiconducting supramolecular Mg(II)-metallohydrogel derived from an aliphatic amine: a robust resistive switching framework for brain-inspired computing

A rapid metallohydrogelation strategy has been developed of magnesium(II)-ion using trimethylamine as a low molecular weight gelator in water medium at room temperature. The mechanical property of the synthesized metallohydrogel material is established through the rheological analysis. The nano-rose like morphological patterns of Mg(II)-metallohydrogel are characterized through field emission scanning electron microscopic study. The energy dispersive X-ray elemental mapping analysis confirms the primary gel forming elements of Mg(II)-metallohydrogel. The possible metallohydrogel formation strategy has been analyzed through FT-IR spectroscopic study. In this work, magnesium(II) metallohydrogel (Mg@TMA) based metal–semiconductor-metal structures have been developed and charge transport behaviour is studied. Here, it is confirmed that the magnesium(II) metallohydrogel (Mg@TMA) based resistive random access memory (RRAM) device is showing bipolar resistive switching behaviour at room temperature. We have also explored the mechanism of resistive switching behaviour using the formation (rupture) of conductive filaments between the metal electrodes. This RRAM devices exhibit excellent switching endurance over 10,000 switching cycles with a large ON/OFF ratio (~ 100). The easy fabrication techniques, robust resistive switching behaviour and stability of the present system makes these structures preferred candidate for applications in non-volatile memory design, neuromorphic computing, flexible electronics and optoelectronics etc.

Self-powered AlGaN-based MSM solar-blind ultraviolet photodetectors with high Al-content AlxGa1−xN/AlyGa1−yN asymmetrical heterostructure

An Al0.4Ga0.6N-based metal–semiconductor–metal (MSM) ultraviolet (UV) photodetector (PD) based on intentionally asymmetrical polarized Al0.55Ga0.45N/Al0.4Ga0.6N/Al0.65Ga0.35N heterostructure has been fabricated and investigated, which achieves the self-powered capabilities. Operated at zero bias, the device presents an ultralow dark current of 7.8 × 10−13 A, a high peak responsivity of 0.04 A/W at ∼275 nm, a cut-off wavelength at ∼285 nm, and a corresponding detectivity of 3.1 × 1012 Jones. In comparison, the device with symmetrical heterostructure has no response at 0 V, confirming the effect of the proposed asymmetrical MSM structure. Furthermore, it is expressly demonstrated that the structure provides an asymmetrical energy band due to different barrier heights at the metal/Al0.4Ga0.6N and metal/Al0.55Ga0.45N/Al0.4Ga0.6N Schottky contacts and enhances the built-in electric field in the Al0.4Ga0.6N active layer owing to its polarization effect through simulations theoretically. Therefore, the improvement of photogenerated carrier transport can be obtained at 0 V, contributing to the high-performance self-powered UV PD.

Low resistance large area terahertz detector based on antimony telluride thin film

Terahertz technology has great potential for various applications in fields like biomedicine, astronomy, communications, and security inspection. Therefore, terahertz detectors that can operate at room temperature with fast response times, high sensitivity, wide detection bandwidth, and can be seamlessly integrated. To achieve this, a metal–semiconductor-metal structure with a subwavelength gap is used, which creates an electromagnetic induced potential well within the semiconductor by utilizing the antisymmetric electric field of terahertz radiation. This structure allows for the injection and retention of electrons from the metal, enhancing electrical conductivity. Experimental results have shown that reducing the spacing between the forked finger electrodes improves the detection performance of the device. At room temperature, with a bias voltage of 1 V and 0.28 THz radiation, the device achieves an equivalent noise power of 9.76 × 10−13 W/Hz/2 and a detection rate of 2.41 × 1011cm Hz1/2W−1. Additionally, the device's simple structure and large effective detection area make it suitable for producing low-resistance and large-area terahertz detectors.

Construction of organic/GaN heterostructures for DUV-to-NIR broadband photodetection.

Herein, a broadband photodetector (BPD) is constructed with consistent and stable detection abilities for deep ultraviolet to near-infrared spectral range. The BPD integrates the GaN template with a hybrid organic semiconductor, PM6:Y6, via the spin-coating process, and is fabricated in the form of asymmetric metal-semiconductor-metal structure. Under an optimal voltage, the device shows consistent photoresponse within 254 to 850 nm, featuring high responsivity (10 to 60 A/W), photo-to-dark-current ratio over 103, and fast response time. These results show the potential of such organic/GaN heterojunctions as a simple and effective strategy to build BPDs for a reliable photo-sensing application in the future.