Good Rectification Properties Research Articles

Enhancing photo-response performance through ultrathin Al2O3 modification at the p-SnO2:Al/n-GaN heterojunction interface

We report on photoconductive and p-n heterojunction ultraviolet (UV) photodetectors based on p-type Al-doped SnO2 (p-SnO2:Al) thin films. We investigated the structural, optical, and electrical properties of Al-doped SnO2 thin films prepared using sol-gel methods, with our results being strongly supported by first-principles calculations. To achieve a self-powered photodetector device at zero bias, we fabricated p-SnO2:Al thin film on an n-GaN layer to form a p-n heterojunction. The responsivity of the p-n heterojunction UV detector, measured at zero bias, is 0.05 A/W, indicating good rectification properties. In order to improve device performance, a p-n heterojunction with a passivation layer was formed by inserting an ultrathin Al2O3 layer between the n-GaN layer and the p-SnO2:Al layer. With this change, the device's responsivity was 0.44 A/W at 350 nm at zero bias, roughly 10 times better than the detector without the Al2O3 passivation layer. The insertion of an ultrathin Al2O3 layer, which increases the efficiency of carrier separation on the SnO2 side while lowering the rate of carrier recombination at the interface, is responsible for the increased light responsivity performance.

High-photoresponsivity heterojunction based on MoTe2/2D electron gas at the LaAlO3/SrTiO3 interface

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are ideal elements for many optoelectronic devices owing to their outstanding optoelectrical performance under visible and infrared light. Heterostructures composed of TMDs and other non-TMD materials may exhibit rich properties. In this study, a high-performance heterojunction based on 2D MoTe2 and 2D electron gas (2DEG) at the LaAlO3/SrTiO3 interface was fabricated. The device exhibits good current rectification properties with a high rectification ratio exceeding 103 and a low leakage current (∼1 nA at −6 V bias). Moreover, a high photoresponsivity of ∼800 A W−1 and a large specific detectivity of 4 × 1012 Jones at 405 nm were also obtained at room temperature. Heterostructures based on 2D TMDs and oxide 2DEG are expected to become essential elements in multifunctional microdevices and optoelectronic devices.

Band alignment and electrical properties of NiO/β-Ga2O3 heterojunctions with different β-Ga2O3 orientations

Due to the difficulty of p-type doping in β-Ga2O3, NiO/β-Ga2O3 heterojunction becomes a promising candidate for fabricating bipolar devices. In this work, we performed a comparative study on the band alignment and electrical properties of the NiO/β-Ga2O3 heterojunctions with different β-Ga2O3 orientations. NiO thin films were sputtered on three β-Ga2O3 substrates with (−201), (001) and (010) orientations and were subsequently fabricated into NiO/β-Ga2O3 heterojunction diodes. A type-Ⅱ band alignment between the NiO and β-Ga2O3 was identified by the transmittance spectra and X-ray photoelectron spectroscopy (XPS) measurements. The valence band offsets (VBOs) of the NiO/β-Ga2O3 heterojunctions on (−201), (001) and (010) substrates were determined to be (2.12 ± 0.06) eV, (2.44 ± 0.07) eV and (2.66 ± 0.07) eV, respectively, and their corresponding conduction band offsets (CBOs) were (1.22 ± 0.06) eV, (1.49 ± 0.07) eV and (1.86 ± 0.07) eV. In addition, the fabricated heterojunction diodes showed good rectification properties with different turn-on voltages, which was in good agreement with the XPS results. The revealed influence of substrate orientations on the properties in NiO/β-Ga2O3 heterojunctions were of great importance for the design and optimization of β-Ga2O3-based heterojunction devices.

Construction of n-SnO2 microwire/p-InGaN heterojunction for self-powered and broadband photodetector

The self-biased photodetectors without an external power source, which have been extensively utilized in wireless communication, imaging, light-sensing and so on, are urgently in demand. In this study, we successfully constructed a self-energized photodetector on the basis of n-SnO2 microwire/p-InGaN heterojunction, which exhibits an good current rectification property in darkness and superior photovoltaic behaviors upon ultraviolet–visible (330–530 nm) light irradiation. Under 360 nm light irradiation, the designed photodetector reveals a superior photoresponsivity surpassing 152.5 mA/W, a high detectivity exceeding 3.77 × 1012 Jones, a fast response speed (the rising/decaying times ∼0.2/14.6 ms) and a high Ion/Ioff ratio over 105 when operated in a self-driven manner. Additionally, the responsivities of our self-powered photodetector were derived to about ∼85.2 and 5.5 mA/W upon illumination with visible light of 405 and 532 nm, respectively. The highly-sensitive broad-spectrum photodetection mechanism of the as-constructed n-SnO2 microwire/p-InGaN heterojunction is resulted from the combination of ultraviolet-sensitive SnO2 monocrystals and visible-sensitive capability of InGaN material. The resultant photoresponse properties of the designed n-SnO2 microwire/p-InGaN heterojunction photodetector that having merits of low cost and facile construction, can enable a competitive and potential candidate with prospect of developing high-performance self-biased photodetectors in the broadband ranging from ultraviolet to visible.

Diamond Schottky barrier diodes fabricated on sapphire-based freestanding heteroepitaxial diamond substrate

In this study, diamond Schottky barrier diodes (SBDs) fabricated on a sapphire-based heteroepitaxial diamond substrate were demonstrated. For commercializing diamond-based power electronics, a large-sized heteroepitaxial diamond substrate is essential. Sapphire is one of the most promising candidates among the diamond heteroepitaxial substrates because it can be produced on a large scale and its thermal expansion coefficient is similar to that of diamond, compared to that of any other non-diamond hetero substrate. The current-voltage characteristics of heteroepitaxial diamond SBDs grown under different growth rates were analyzed, and good rectification properties of SBDs were observed at the device grown with low growth rate. The ideality factor was 1.4, and the maximum breakdown field was approximately 1.1 MV/cm. The value of built-in potential derived from the capacitance-voltage characteristics was in good agreement with the approximated barrier heights. Some ball-shaped features on the SBD along the threading dislocation were directly observed after performing the breakdown test under reverse bias condition using transmission electron microscope (TEM). Threading dislocation which induces breakdown or large leakage current under reverse bias in diamond SBD was clarified and this will lead the research direction of a heteroepitaxial diamond electronic device. Prime novelty statementsRecently, the diamond SBD grown on large-size heteroepitaxial diamond substrates becoming alternative to conventional high temperature high pressure (HPHT) diamond-based diamond SBD. In this study, diamond SBD grown on sapphire-based freestanding heteroepitaxial diamond substrate was successfully demonstrated. The sapphire substrate is one of the most promising material as substrate for heteroepitaxial diamond which is low cost and large sized. The heteroepitaxial diamond SBD structures with different growth rate were grown using microwave plasma CVD (MPCVD) and its structural properties were characterized. After device fabrication process, the detailed analysis of electrical properties of SBD were carried out. The direct observation of breakdown and leakage current features on SBD was obtained before and after electrical test under reverse bias condition.

Camphor-Based CVD Bilayer Graphene/Si Heterostructures for Self-Powered and Broadband Photodetection.

This work demonstrates a self-powered and broadband photodetector using a heterojunction formed by camphor-based chemical vaper deposition (CVD) bilayer graphene on p-Si substrates. Here, graphene/p-Si heterostructures and graphene layers serve as ultra-shallow junctions for UV absorption and zero bandgap junction materials (<Si bandgap (1.1 eV)) for long-wave near-infrared (LWNIR) absorption, respectively. According to the Raman spectra and large-area (16 × 16 μm2) Raman mapping, a low-defect, >95% coverage bilayer and high-uniformity graphene were successfully obtained by camphor-based CVD processes. Furthermore, the carrier mobility of the camphor-based CVD bilayer graphene at room temperature is 1.8 × 103 cm2/V·s. Due to the incorporation of camphor-based CVD graphene, the graphene/p-Si Schottky junctions show a good rectification property (rectification ratio of ~110 at ± 2 V) and good performance as a self-powered (under zero bias) photodetector from UV to LWNIR. The photocurrent to dark current ratio (PDCR) value is up to 230 at 0 V under white light illumination, and the detectivity (D*) is 8 × 1012 cmHz1/2/W at 560 nm. Furthermore, the photodetector (PD) response/decay time (i.e., rise/fall time) is ~118/120 μs. These results support the camphor-based CVD bilayer graphene/Si Schottky PDs for use in self-powered and ultra-broadband light detection in the future.

High responsivity ZnO based p–n homojunction UV-photodetector with series Schottky barrier

In the present article, we proposed a p–n homojunction photodetector with a series Schottky barrier and a high value of responsivity in the ultraviolet region. The thin-film photodetector makes use of a junction between an RF-sputtered n-type ZnO nanostructure and a p-type copper doped ZnO (CZO) thin film derived through the spin coating process on an ITO coated glass substrate. Palladium metal contacts have been deposited to form the Schottky barrier in series with the p–n homojunction. The device has been simulated, fabricated, and tested only after ensuring the stability of the p-type CZO thin film. The measured I–V characteristics of the fabricated photodetector under illuminated and dark conditions showed excellent UV response and good rectification properties. The device exhibits a peak responsivity of 13.2 A W−1 for a reverse biasing voltage of 3 V. This value is much higher than the values reported by others for a ZnO based photodetector.

Design of a piezoelectric energy harvesting device based on ZnO–Na2Ti6O13 heterojunction nanogenerator

Enhancing the performance of nanogenerators is vital in the development of new piezoelectric applications that reveal high sensitivity to the surrounding waste of mechanical vibrational energy. In this paper, two major solutions are presented. The first is an easy and low-cost nanogenerator method utilizing Disodium Hexatitanate (Na2Ti6O13) as an alkali catalyzed material for growing the ZnO seed layer. The second solution is to suppress the screening effect that takes place in ZnO-metal harvester by forming a ZnO–Na2Ti6O13 heterojunction harvester. In other words, improvement can be realized by adopting a p-n junction approach instead of using the traditional Schottky contact approach. The ZnO–Na2Ti6O13 nanogenerator was grown hydrothermally. The size and nanofiber’s shape, material compounds distribution in the p-n junction and the crystal phases are investigated. The result was a fabricated ZnO nanofiber with a length and diameter of 3.726 μm and 0.158 μm respectively and the average crystal size of the Na2Ti6O13 nanofiber was 97.74 nm, with a fiber diameter of approximately 8.699 nm. The maximum AC voltage (Vpk-pk) and current upon finger pressing reached about 2 V and 2 μAcm−2 respectively. A good rectification property resulted based on the use of a p-n junction approach. The ZnO–NTO nanofiber could provide DC voltage up to 3.6 V where the derived energy is sufficient to power LCD digital screen.

X-Ray Detector Based on p+-Si/n-Zn2SiO4 Heterojunction Diode

p+-Si/n-Zn2SiO4 heterojunction diodes were fabricated on Si substrate, and tested as X-ray detector for the first time in this letter. The devices exhibited good rectification properties at dark current, and the dark current density was $\sim 5.6\times 10^{\mathbf {-6}}$ A/cm2 at −40 V. An obvious response to X-ray illumination (generated by bremsstrahlung with a tungsten target with tube voltage 30 kV) was observed at reversed bias, and the photo-to-dark ratio exceeding 480 was achieved. Furthermore, the detector exhibited both photoconductive behavior and photovoltaic behavior to switching X-ray illumination, and response time and recovery time are discussed on both mechanisms. In addition, the detector showed fast response time less than 200 ms and the linear outputs against incident X-ray dose rate from 0.383 Gy/s to 4.596 Gy/s at zero-bias voltage. The results imply that the ultra-wide band gap Zn2SiO4 based junction-type detectors have the potential for passive X-ray dose detection and nuclear battery cell applications.

Solution-Processed TiO2-Based Schottky Diodes With a Large Barrier Height

Thin-film Schottky diodes are one of the key elements in large-area flexible electronics. In such devices, a highly uniform semiconductor film is vital for the device performance. Here, we propose a novel solution-based anodization method to form a conformal oxide semiconductor layer for Schottky diodes. The thickness of the anodized TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer varied from 12 to 22.5 nm. The optimized Pt/TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Ti Schottky diode demonstrated a large barrier height of 1.19 eV, an ON/OFF ratio as high as 3.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> at ± 2 V, and an ideality factor of 1.5. The average breakdown electric field was 5.5 MV/cm, which is higher than typical values of conventional solution processed TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The diode with a 15-nm-thickTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer also showed good rectification properties up to 0.7 MHz.

β‐Ga2O3/p‐Type 4H‐SiC Heterojunction Diodes and Applications to Deep‐UV Photodiodes

Here, pn heterojunction diodes based on β‐Ga2O3/p‐type 4H‐SiC structures are fabricated. The current–voltage characteristics of the diodes are measured in the temperature range from 23 to 500 °C. These diodes exhibit good rectification properties and stability under high temperatures. The rectification ratios exceed 1000 even at 500 °C. Deep‐ultraviolet (deep‐UV) photodiodes are fabricated on the basis of heterojunctions having various β‐Ga2O3 thicknesses, which present the maximum responsivity at 250–260 nm and respond to UV pulses as short as ≈30 μs in real time.

Schottky x-ray detectors based on a bulk β-Ga2O3 substrate

β-Ga2O3 Schottky barrier diodes (SBDs) have been fabricated on a bulk (100) β-Ga2O3 substrate and tested as X-ray detectors in this study. The devices exhibited good rectification properties, such as a high rectification ratio and a close-to-unity ideality factor. A high photo-to-dark current ratio exceeding 800 was achieved for X-ray detection, which was mainly attributed to the low reverse leakage current in the β-Ga2O3 SBDs. Furthermore, transient response of the β-Ga2O3 X-ray detectors was investigated, and two different detection mechanisms, photovoltaic and photoconductive, were identified. The results imply the great potential of β-Ga2O3 based devices for X-ray detection.

Beta-Gallium Oxide/SiC Heterojunction Diodes with High Rectification Ratios

We fabricated diodes based on beta-gallium oxide (β-Ga2O3)/p-type 6H–SiC heterojunctions. Because the barrier height for electrons in β-Ga2O3 is much lower than the barrier height for holes in 6H–SiC, only the injection of electrons can be treated in the heterojunction. The diodes have good rectification properties even at high temperatures of up to 500°C. A breakdown voltage of over 350 V was obtained in the diode with a 233-nm-thick layer of β-Ga2O3. In the high-temperature measurements, the dependences of the rectification ratio and reverse current on temperature were evaluated and discussed. The β-Ga2O3/6H–SiC heterojunction diode has a remarkably low reverse saturation current and very high potential as a rectifier.

Effect of Light Intensity and Temperature on the Current Voltage Characteristics of Al/SY/p-Si Organic–Inorganic Heterojunction

An organic–inorganic contact was fabricated by forming a thin film of sunset yellow dye (SY) on a p-Si wafer. The device showed a good rectification property, and the sunset yellow thin film modified the barrier height (Φb) of Al/p-Si contact by influencing the space charge region. The heterojunction had a strong response to the different illumination intensities and showed that it can be suitable for photodiode applications. The I–V measurements of the device were also applied in the temperature range of 100–500 K. It was seen that characteristic parameters of the device were strongly dependent upon temperature. While the value of Φb increased, the ideality factor (n) decreased with the increase in temperature. This variation was attributed to spatial inhomogeneity at the interface. The Norde function was used to determine the temperature-dependent series resistance and Φb values, and there was a good agreement with that of ln I–V data. The values of the Richardson constant (A*) and mean Φb were determined as 29.47 Acm−2 K−2 by means of a modified activation energy plot, matching with a theoretical one, and 1.032 eV, respectively. Therefore, it was stated that the current voltage characteristic with the temperature can be explained by thermionic emission theory with Gaussian distribution of the Φb at the interface.

Robust hybrid hydrogels with good rectification properties and their application as active materials for dye-sensitized solar cells: insights from AC impedance spectroscopy

A robust tri-hybrid hydrogel containing GO exhibits excellent rectification properties and acts as an active material for DSSCs showing an efficiency of 4.5%.

Free exciton luminescence from a diamond p–i–n diode grown on a substrate produced by heteroepitaxy

We fabricated diamond p–i–n diodes with homoepitaxially grown films on a heteroepitaxial diamond (001) substrate produced with diamond films grown on iridium (Ir). We applied our state‐of‐the‐art techniques on single crystal diamond‐based electronic devices. The current–voltage characteristics of the p–i–n diodes showed good rectification properties. Under forward current operation, the diode showed both free exciton and defect‐related luminescence. When the forward current increased, integrated intensity of defect‐related luminescence increased sub‐linearly, while that of free exciton luminescence increased super‐linearly. This remarkable trend is the same as that observed in a p–i–n diode fabricated with homoepitaxially grown films on the conventional high‐pressure and high‐temperature synthesized diamond single‐crystal substrates. The results obtained in this paper indicate a sufficient potential of the heteroepitaxial diamond substrates grown on Ir for future diamond‐based electronic devices.

Charge transport properties of p-CdTe/n-CdTe/n+-Si diode-type nuclear radiation detectors based on metalorganic vapor-phase epitaxy-grown epilayers

Charge transport properties of p-CdTe/n-CdTe/n+-Si diode-type nuclear radiation detectors, fabricated by growing p-and n-type CdTe epilayers on (211) n+-Si substrates using metalorganic vapor-phase epitaxy (MOVPE), were studied by analyzing current-voltage characteristics measured at various temperatures. The diode fabricated shows good rectification properties, however, both forward and reverse biased currents deviate from their ideal behavior. The forward current exhibits typical feature of multi-step tunneling at lower biases; however, becomes space charge limited type when the bias is increased. On the other hand, the reverse current exhibits thermally activated tunneling-type current. It was found that trapping centers at the p-CdTe/n-CdTe junction, which were formed due to the growth induced defects, determine the currents of this diode, and hence limit the performance of the nuclear radiation detectors developed.

Diode behavior in ultra-thin low temperature ALD grown zinc-oxide on silicon

A thin-film ZnO(n)/Si(p+) heterojunction diode is demonstrated. The thin film ZnO layer is deposited by Atomic Layer Deposition (ALD) at different temperatures on a p-type silicon substrate. Atomic force microscopy (AFM) AC-in-Air method in addition to conductive AFM (CAFM) were used for the characterization of ZnO layer and to measure the current-voltage characteristics. Forward and reverse bias n-p diode behavior with good rectification properties is achieved. The diode with ZnO grown at 80°C exhibited the highest on/off ratio with a turn-on voltage (VON) ∼3.5 V. The measured breakdown voltage (VBR) and electric field (EBR) for this diode are 5.4 V and 3.86 MV/cm, respectively.

MOVPE Growth of Thick Single Crystal CdZnTe Epitaxial Layers on Si Substrates for Nuclear Radiation Detector Development

Details about the MOVPE growth of thick single crystal CdZnTe layers on (211)Si substrates are presented. The growth was carried out at a substrate temperature of 650°C, using dimethylcadmium, dimethylzinc, and diethyltellurium precursors. Control of Zn-concentration in the range from 0 to 0.2 was performed by controlling the precursors' flow-rates and ratio. Results from the XRD showed grown layers were single crystalline with no phase separation observed. The 4.2 K PL results show high intensity bound-exciton peaks which shifted to higher energies with increasing Zn-concentrations. A p-CdZnTe/p-CdTe/n-CdTe/n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -Si hetero-junction diode was fabricated and evaluated for its possible application in nuclear radiation detector development, which exhibited good rectification property.

The barrier height enhancement of the Au/n-Si/Al Schottky barrier diode by electrochemically formed an organic Anthracene layer on n-Si

In this work, an Au/Anthracene/n-Si/Al Schottky barrier diode was fabricated and it was found that the diode showed good rectification properties. The characteristic parameters of the device such as barrier height, ideality factor, interface states density and series resistance were determined from the current–voltage measurements. It was seen that the Anthracene organic layer increased the effective barrier height of the Au/n-Si/Al diode since this layer creates the physical barrier between the Au and n-Si. Furthermore, the current–voltage characteristics under forward bias were found to be ohmic due to conduction at lower voltage regions. At higher voltage regions there is space charge limited conduction (SCLC) mechanism. Furthermore, the capacitance–voltage curves of the Au/Anthracene/n-Si/Al Schottky barrier diode were analyzed in the various frequencies as a function of the bias.