Heterojunction Diodes Research Articles

Titanium oxide decorated zinc oxide nanoparticles for dye-sensitized solar cell and heterojunction diode applications

Titanium oxide decorated zinc oxide nanoparticles for dye-sensitized solar cell and heterojunction diode applications

(Invited) Optical Properties and Device Application of One-Dimensional Vdw Heterostructures Based on Single-Walled Carbon Nanotubes

A typical one-dimensional (1D) van der Waals (vdW) heterostructure consists of SWCNT, boron nitride nanotube (BNNT), and molybdenum disulfide nanotube (MoS2NT), grown coaxially by successive chemical vapor deposition (CVD) steps [1, 2]. The coaxially nested structure based on SWCNTs, which has diverse electronic properties (metallic or semiconducting), can expand the board application possibilities of 1D vdW heterostructures [3]. By comparing the optical properties of films of BNNT@MoS2NT and SWCNT@BNNT@MoS2NT, we found strong photoluminescence (PL) from monolayer MoS2NT and quenching of PL by coupling to SWCNT through thin BNNT [4]. The inter-tube excitons are demonstrated by ultrafast optical spectroscopy [5]. The inter-tube excitons, the counterpart of inter-layer excitons for 2D heterostructures, suggest a possibility of efficient photovoltaic applications of the 1D heterostructure [6]. In addition to MoS2 nanotubes, we will discuss the growth control of WS2 and NbS2 nanotubes. A general strategy we can tune the CVD condition from 2D flake to 1D tube is proposed. The junctions of MoS2 and WS2 nanotube are also realized as the outermost layer. More specific optical properties are studied for semiconductor SWCNTs and chirality-sorted SWCNTs [7,8]. Semiconductor SWCNT or chirality-sorted SWCNT wrapped with BNNT can be regarded as the ideal building blocks of field-effect transistors (FET) [9]. We have demonstrated the radial semiconductor–insulator–semiconductor (S-I-S) tunneling heterojunction diode by using a micrometer long 1D vdW heterostructure SWCNT@BNNT@MoS2NT [10]. We will discuss a more recent array of 1D heterostructure FET devices.Part of this work was supported by JSPS KAKENHI Grant Number JP20H00220, and by JST, CREST Grant Number JPMJCR20B5, Japan.

The evaluation of the Al/ZnO/Si/Al heterojunction diode current-conducting mechanisms

This work focuses on the electrical transport and conduction mechanisms — inside a sprayed — made zinc oxide-on-p-type silicon junction device. A fabricated Al/ZnO/Si/Al heterojunction is characterized at 300 and 380[Formula: see text]K in the dark. The aforementioned theories predict that the current density (J) is an exponential function of measured voltage (V) and work temperature (T). Exponential equations are linearized as a result of a current conduction mechanism (CCM) kind. Useful parameters like barrier height [Formula: see text] of trap are extracted from the slope B. Ohmic and space charge limited current (SCLC) regimes inside are studied at 300 and 380[Formula: see text]K recording a shift in exponent as a result of temperature. Fowler–Nordheim (FN) conduction mechanism inside Al/ZnO/Si/Al device is considered slope and [Formula: see text] values are determined for two cited work temperatures. Our device presents a thermionic emission (TE) and exhibits an effect of temperature on slope and intercept values of (ln[Formula: see text]/A*[Formula: see text]) function. The Poole–Frenkel (PF) emission in terms of 1/V data are presented for 300 and 380[Formula: see text]K. Besides, PF emission mechanism in terms of 1/[Formula: see text] is exhibited and parameters are influenced by temperature. Behavior of conductance as a result of temperature is detailed and evidenced.

Characteristics of ZnON films and heterojunction diodes with varying O:N ratios

Zinc Oxynitride (ZnOxNy) thin films display high mobilities and a considerable tunability of both the free electron concentration and optical band gap. The properties achievable for this material system makes ZnOxNy an intriguing n-type absorber candidate in silicon-based tandem solar cells. We have studied how the O:N ratio affect structural, optical and electrical properties of magnetron sputtered ZnOxNy thin films, as well the electrical behavior of ZnOxNy-Si pn heterojunction diodes. X-ray diffraction of the ZnOxNy films indicate either a Zn3N2-like structure or ZnO-like grains in combination with structural disorder. As the O:N ratio is increased, the optical band gap of ZnOxNy films increase from 1.1 to 1.9 eV. Hall effect measurements of the n-type ZnOxNy films show free electron concentrations varying with the O:N ratio, from 9.8×1017 to 1.5×1016 cm−3. Hall mobility up to 88 cm2/Vs is achieved. We observe the formation of pn heterojunction diodes between ZnOxNy-films and p-Si. The electrical characteristics of these diodes are shown to depend on the ZnOxNy anion composition. Current rectification of 3.7 orders of magnitude is achieved between -1 and 1 V at room temperature. However, the built in voltage extracted from capacitance–voltage measurements are higher than theory suggest, implying an influence of defects on the electrical characteristics.

A self-aligned Ga2O3 heterojunction barrier Schottky power diode

We report an alignment-free gallium oxide (Ga2O3) heterojunction barrier Schottky (HJBS) power diode, which utilizes the self-assembled Ni nanostructures as in situ masks for the trench etching of Ga2O3 and the subsequent selective-area filling of p-type NiO. By increasing the trench depth to 200 nm, the relevant HJBS diode exhibits improved reverse blocking capabilities including the reduced leakage current density of 10−8 A/cm2 (at a reverse bias of 100 V) and the enhanced breakdown voltage of 748 V, while maintaining the forward biasing characteristics similar to the Schottky barrier diode (SBD). The variation of turn-on voltage and the reverse breakdown features indicate the conversion of the HJBS diodes characteristics from Ni/Ga2O3 SBD to the NiO/Ga2O3 p-n heterojunction diode. The electrical field simulations and experimental facts imply that the remarkable lateral pinch-off effect in the 200-nm trenched diodes shields the electric field in the depletion region underneath the Ni/Ga2O3 Schottky contact. This work provides a straightforward strategy to simplify the fabrication process of Ga2O3-based HJBS diodes with both promising forward and reverse performances.

2.83-kV double-layered NiO/β-Ga2O3 vertical p-n heterojunction diode with a power figure-of-merit of 5.98 GW/cm2

This work demonstrates high-performance NiO/β-Ga2O3 vertical heterojunction diodes (HJDs) with double-layer junction termination extension (DL-JTE) consisting of two p-typed NiO layers with varied lengths. The bottom 60-nm p-NiO layer fully covers the β-Ga2O3 wafer, while the geometry of the upper 60-nm p-NiO layer is 10 μm larger than the square anode electrode. Compared with a single-layer JTE, the electric field concentration is inhibited by double-layer JTE structure effectively, resulting in the breakdown voltage being improved from 2020 to 2830 V. Moreover, double p-typed NiO layers allow more holes into the Ga2O3 drift layer to reduce drift resistance. The specific on-resistance is reduced from 1.93 to 1.34 mΩ·cm2. The device with DL-JTE shows a power figure-of-merit (PFOM) of 5.98 GW/cm2, which is 2.8 times larger than that of the conventional single-layer JTE structure. These results indicate that the double-layer JTE structure provides a viable way of fabricating high-performance Ga2O3 HJDs.

Structural, electrical and optical properties of samarium fluoride doped SnO2 transparent conducting oxide thin films for optoelectronic device applications

In this study, p-type transparent tin oxide (SnO2) based semiconductor thin films were deposited onto glass substrates by sol-gel dip-coating method using samarium-trifluoride (SmF3) as acceptor dopant. The films were prepared by co-doping 2 mol.% of SmF3 into SnO2 (SFTO), followed by annealing temperature at 475 °C. XRD analysis results showed that the films exhibited the tetragonal rutile SnO2 phase. The p-type conductance of the SFTO films were confimed by Hall effect and Seebeck coefficient measurements. Resistivity and mobility of the SmF3 doped SnO2 film is 7.83 × 10–3Wcm and 7.57 cm2 V–1 s–1, respectively, which reduce in comparing with those of un-doped SnO2 film. Carrier concentration is large increase from –9.34 ´ 1018 cm–3 for un-doped- to +1.05 × 1020 cm–3 for SmF3 doped-SnO2 film. The p-type SFTO film showed a high transmittance of 74.3% at 550 nm, with band gap energy of 3.63 eV. Furthermore, a transparent p-SnO2:SmF3/n-ZnO:Al (Al doping level of 2 mol.%) heterojunction was fabricated on alkali-free glass substrates. The I-V curve measurement for the p-n heterojunction diode showed a typical rectifying characteristic with a forward turn-on voltage of 1.55 V. With obtained properties, the p-type SFTO film holds great promise for optoelectronic devices applications.

Investigation of deep defects and their effects on the properties of NiO/β-Ga2O3 heterojuncion diodes

In this study, the effect of rapid thermal annealing (RTA) on the electrical and optical properties of NiO/ β-Ga2O3 heterojunction diodes was investigated using capacitance-voltage, current-voltage, Deep Level Transient Spectroscopy (DLTS), Laplace DLTS, photoluminescence and micro-Raman spectroscopy techniques, and SILVACO-TCAD numerical simulator. The NiO is designed to be lowly-doped, allowing for the NiO full depletion at zero bias and the study of properties of β-Ga2O3 and its interface with NiO. Micro-Raman results revealed good agreement with the theoretical and experimental results reported in the literature. The photoluminescence intensity of the sample after RTA is five times higher than the fresh sample due to a rise in the density of gallium and oxygen vacancies (VGa + VO) in the annealed β-Ga2O3 samples. The current-voltage characteristics showed that annealed devices exhibited a lower ideality factor at room temperature and higher barrier height compared with fresh samples. The DLTS measurements demonstrated that the number of electrically active traps were different for the two samples. In particular, three and one electron traps were detected in fresh samples and annealed samples, respectively. SILVACO-TCAD was used to understand the distribution of the detected electron E2 trap (Ec-0.15 eV) in the fresh sample and the dominant transport mechanisms. A fairly good agreement between simulation and measurements was achieved considering a surface NiO acceptor density of about 1 × 1019 cm−3 and E2 trap depth into the surface of β-Ga2O3 layer of about 0.220 µm and the effect of the most observed Ec-0.75 eV trap level in β-Ga2O3. These results unveil comprehensive physics in NiO/β-Ga2O3heterojunction and suggest that RTA is an essential process for realizing high-performance NiO/β-Ga2O3devices.

A Novel Shield Gate 4H-SiC MOSFET with Reduced Reverse Recovery Losses

In this work, a novel integrated shield gate 4H-SiC MOSFET structure, which is mainly used to reduce the reverse recovery losses of the device, is proposed. Compared with integrating Schottky barrier diode or heterojunction diode in the device to reduce reverse recovery losses, the technology of introducing field plates in MOSFETs is more mature and economical. At the same time, the new structure studied ensures the gate oxide reliability of the 4H-SiC trench gate. According to the simulation of the electrical characteristics of the source-contacted shield gate device, the effects of multiple factors such as electric field distribution, carrier concentration, and peripheral circuit are comprehensively discussed, the phenomenon of smaller reverse recovery losses caused by the shield gate explained in detail. Compared with the conventional structure device, the peak reverse current, the peak overshoot voltage, and the reverse recovery losses for the source-contacted shield gate MOSFETs are reduced by 81.4%, 77.1%, and 65.1%, respectively.

Doping Density Extraction of Plasma Treated Metal Oxide Thin Film Diodes by Capacitance–Voltage Analysis

AbstractHigh quality thin film p‐n junction diodes with high rectification ratios and low ideality factors have been fabricated from metal oxides, such as amorphous oxide semiconductors (AOSs), and characterized. Plasma treatment of interfaces has been demonstrated to improve devices made from AOSs, using current–voltage (I–V) measurements. However, capacitance–voltage (C–V) measurements of the devices have been scarcely reported in the literature. Therefore, the focus of this work is characterization of cuprous oxide (Cu2O)/amorphous zinc‐tin oxide (a‐ZTO) thin film heterojunction diodes using C–V analysis. Performance differences of plasma‐treated and untreated diodes that are difficult to observe in I–V analysis are more prominent in C–V analysis. Moreover, C–V analysis allows extraction of charge density profiles, which is a measure of the defect state density that led to intrinsic doping. The variation of doping densities of the untreated diode across the full range of applied reverse bias is shown to be up to 2 orders of magnitude, while those of the treated diodes are within a factor of 10 only. Junction charge profiles, interfacial charge depletion, and accumulation that are key features of rectifying diodes are shown to be clearly distinct between untreated, nitrogen‐treated, and oxygen‐treated diodes, thus explaining why oxygen‐treated diodes are superior.

Enhanced conductivity of infrared transparent Bi2Se3 thin films as anti-interference coatings for infrared detectors

Infrared transparent conductive coatings are extensively utilized in both military and civilian infrared detectors due to their superior infrared transmission and electromagnetic shielding properties. It is a major scientific challenge to find a solution to the contradiction between high transmittance and low conductivity in the area of wide-band infrared transparent conductive film research. This study utilized new material systems and film preparation technologies to clarify the problem. A higher c-axis preferred orientation infrared transparent conducting Bi2Se3 thin film on a p-Si (111) substrate was developed using plasma-enhanced chemical vapor deposition (PECVD) technology. At room temperature, the film exhibited n-type conductivity, with high surface mobility of 2565 cm2/V·s and low surface resistivity of 2.6 × 10−5 Ω cm. In the mid-IR and far-IR regions, the produced Bi2Se3 thin film displayed transparency of 90% and 80%, respectively. To the best of our knowledge, this n-type conductive thin film created using chemical vapor deposition is the best IR-transparent thin film to date. Using this film, a Bi2Se3/p-Si heterojunction diode with a maximum voltage of 0.7 V was created. Young's modulus and hardness were determined to be 80 ± 5.5 GPa and 15 ± 2.2 GPa, respectively, for the film. It demonstrates the film's resistance to wear and deformation. The findings imply that Bi2Se3 film may be used as an anti-interference coating for infrared detectors and other optoelectronic devices throughout a wide wavelength range, from the mid-IR to the far-IR, due to its good optical transparency and electrical conductivity.

Effect of PTAA and PCBM concentrations on the electrical response of bilayer heterojunction PTAA/PCBM Diode

Poly[bis(4-phenyl) (2,4,6-trimethylphenylamine] (PTAA) is a new promising hole transport material, and [6,6]-Phenyl C61 butyric acid methyl ester (PCBM) is a suitable electron acceptor material. This study deposited thin-film PTAA and PCBM at different spin coatings ranging from 1000 rpm to 5000 rpm. Ultraviolet–visible (UV–vis) spectrometer, X-ray diffraction (XRD) machine, and scanning electron microscope (SEM) techniques were used to determine the optical properties and structural properties, respectively. Thermal annealing with temperatures of 80 °C, 100 °C, 120 °C, and 150 °C was introduced to improve the properties of the PTAA and PCBM thin film. The results of SEM images for PTAA annealed at 150 °C appeared to darken and melt, whereas PCBM annealed at 120 °C and 150 °C had granule properties. The ideality factors for bilayer heterojunction diodes and bulk heterojunction PTAA/PCBM diodes with increased layers were 5.8–60.2 and 30.8–77.2, respectively. The optimum spin rate for the bilayer heterojunction PTAA/PCBM was 5000 rpm. The most appropriate diode behavior of the bilayer was at 5.0/1.0 wt%, 1.0/5.0 wt%, and 3.0/3.0 wt% of PTAA/PCBM, with the calculated ideality factors of 5.8, 6.2, and 15.45 with turn-on voltage of 1.57 V, 1.70 V, and 1.82 V, respectively.

Substrate heat-assisted spray pyrolysis of crack-free ytterbium sesquioxide-Si heterojunction diodes for photo-sensing applications

A simple spray pyrolysis is used to develop ytterbium sesquioxide (Yb2O3) on aluminoborosilicate glass substrates at variable substrate temperatures. A cubic crystal system grows along the (222) plane as substrate temperature changes from 600 to 700 °C. Dispersed grains become cluster-like particles in film structures as the temperature rises. The Yb2O3 composition purity.is further ensured by energy dispersive x-ray analyses. Structure improves with optical spectrum transparency. The altered crystallite and grain size shifted the bandgap energy to higher wavelengths. Regarding Ag/n-Yb2O3/p-Si/Ag heterojunction diode performance, the barrier height increases from 0.67 to 0.70 as the substrate temperature rises. The film structure at 700 °C exhibited the best results, including an electrical conductivity of 2.503×10–15 S/cm and an activation energy of 0.129 kJ/mol. In addition, the estimated ideality factors (n) are 4.5 and 2.9 under dark and light conditions, respectively.

Traps inhomogeneity induced conversion of Shockley–Read–Hall recombination in NiO/β-Ga2O3 p+–n heterojunction diodes

In this Letter, the trap inhomogeneity within β-Ga2O3 is correlated with the conversion of Shockley–Read–Hall (SRH) recombination in NiO/β-Ga2O3 p+–n heterojunction diodes. For the virgin epi-wafer, both near-surface traps E2 (EC-0.82 eV) and E3 (EC-1.11 eV) and bulk E2* traps (EC-0.76 eV) are identified by a transient capacitance analysis, and the corresponding forward current–voltage characteristics of diodes are well fitted in the framework of field-dependent SRH recombination. The SRH recombination rates for E2, E3, and E2* traps are determined to be 1.3 × 107, 8.6 × 108, and 2.4 × 108 s−1, respectively. In this circumstance, carrier transport under forward bias is governed by trap-assisted tunneling through E3 traps with high recombination rates, and the hysteresis is pronounced. With the removal of the defective surface layer, E2 and E3 traps are almost completely eliminated, together with the reduced density of E2* traps to 5.6 × 1014 cm−3. The resultant diode performs an improved rectification ratio of >1011 at ±3 V and an enhanced reverse breakdown voltage of 1692 V. The elimination of near-surface traps leads to the conversion of carrier transport into the conventional SRH recombination, accompanied by the negligible forward hysteresis characteristics. The established fundamental correlation of carrier transport and traps within Ga2O3 is beneficial to develop a high-performance power rectifier toward practical applications.

Temperature dependent characteristics of flexible p-PANI/n-ZnO based hybrid heterojunction diode

This study aims to develop and characterize a flexible p-PANI/n-ZnO heterojunction diode developed from a combination of electrochemical and sputtering technique. Investigation of structural properties and morphology of the thin films has been done from XRD and SEM analysis. To study the temperature effect on the electrical properties of the diode, current–voltage–temperature (I–V–T) measurements were done for the temperature range 25–300 K. Applying the ideal thermionic emission theory, various diode parameters like reverse saturation current, quality factor, series resistance and barrier height were computed utilizing the semilogarithmic plot of I–V curve and Cheungs’ method. Barrier height, reverse saturation current and quality factor calculated from ln(I) versus V curve were observed to vary from 0.0627–0.725 eV, 0.236–98.8 nA and 54.43–3.29 respectively over the temperature range 25–300 K. It has been found that the series resistance falls with a rise in temperature. The barrier height, series resistance and ideality factor were observed to vary from 0.0628–0.692 eV, 15 900–46.8 Kohm and 41.88–2.27 respectively for the temperature range 25–300 K. The activation energy estimated from Arrhenius plot was observed to be 14.51 meV. Additionally, the fabricated PANI/ZnO diode was mechanically robust that can be bent without affecting its performance.

Numerical demonstration of SiC trench MOSFET with integrated heterojunction diode for enhanced performance

In this paper, a novel SiC trench-gate MOSFET with integrated heterojunction diode (HD-TG-MOS) is proposed and studied according to TCAD simulations. The n-type polysilicon/n-type SiC HD is introduced into the groove by the direct contact between the polysilicon and semiconductor. As a result, significant improvements of device performance in the first and third quadrants are observed as compared to the conventional SiC trench-gate MOSFET (C-TG-MOS). Better yet, aided by the extremely low barrier height across the heterojunction, the knee voltage reduces to only 0.5 V with comparison of that of ∼2.7 V for the body diode, when used for reverse freewheeling. These promotions make SiC HD-TG-MOS more advantageous for HF power conversion applications. In addition, another cell architecture variant adopting a similar concept is presented, and the according process implementation is addressed as well from viewpoint of manufacture.

High-Performance Photodetectors With Polarization Sensitivity Based on p-n and p-p+ Black Phosphorus/Germanium Heterojunctions

The heterostructures between atomically thin 2-D and 3-D semiconductors show great potential for high-performance photodetector. In this work, the efficient light detection of the p-n and p-p+ black phosphorus (bP)/germanium (Ge) heterojunction photodiode has been demonstrated. With the change of Ge doping type, the rectification direction of the heterojunction diode formed by bP and Ge could be reversed. Due to the enhanced photocarrier separation at the reverse bias, the bP/n-Ge (bP/p-Ge) device has a responsivity of 6.08 (3.43) A/W under 1550-nm illumination, with fast response speed in the 10- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> level. The bP/n-Ge device has a significant photovoltaic effect due to the small conduction band energy offset, with a large open-circuit voltage of 0.34 V. Under the illumination of light with different polarization directions, the device exhibits apparent polarization-sensitive detection, and the dichroic ratio of bP/n-Ge and bP/p-Ge devices is 4.25 and 3.85, respectively. These results suggest that the bP/Ge heterojunction photodetector would have great potential in high-performance, self-powered, and polarization-sensitive photodetection.

Analysis of Electrical Characteristics of N-Doped TiO2 and Si Heterojunction Diodes

Heterojunction photodiodes play a crucial role in various industries and daily life. They find application in fields such as photoelectric detection, aerospace, and intelligent manufacturing. In this study, we employed a series of growth processes, including physical vapor deposition techniques such as magnetron sputtering, high-temperature annealing, and hydrothermal growth, to fabricate N-doped TiO2 heterojunction diode devices with Si as a substrate material. The surface of the device exhibited a columnar array structure with rutile phase TiO2. Additionally, the doping of N element led to the bending of the energy band of TiO2 by approximately 0.2 eV, and the Fermi level also shifted to the valence band, without any effect on the band gap. The I–V characteristics varied in vacuum and air, with ideal factors (η) of 4.1 and 8.72, respectively. The study is expected to broaden the application scope of doped photodiodes.

Influence of Mn doping on electrical properties of TiO2/Si heterojunction diode

AbstractIn this special work, two types of material, which are undoped and Mn doped TiO2thin films, have been produced by spin coating technique, and then their structural, morphological and optical properties have been measured at different Mn doping rates. Four different doping ratios, undoped, 1, 3 and 5% Mn doped TiO2have been both experimentally and theoretically investigated and some significant enhancements have been reported. The results of X-ray diffraction (XRD) such as dislocation density, strain, and crystallite size have indicated that undoped, 1, 3 and 5% Mn doped TiO2thin films had the phase of anatase at 450 °C. It has been observed that the peak intensity of 3% Mn doped TiO2films has decreased compared to undoped and 1% Mn doped TiO2while the peak intensity has increased for 5% Mn doped TiO2. The refractive indices and dielectric coefficients of the undoped and Mn doped TiO2thin films have also been calculated. The undoped and Mn doped TiO2/p-Si heterojunction diodes has exhibited photosensitive behaviour in the illuminated environment. 1% Mn doped TiO2/p-Si heterojunction diode indicated the highest photocurrent. The electrical parameters of all diodes have been calculated and compared to the conventionalJ–Vand Norde methods. Additionally, 1% Mn doped TiO2/p-Si heterojunction diode has been modelled by using the SCAPS-1D program, andJphvalues have also been calculated based on the shallow donor density (ND). The experimental and theoreticalJphvalues of this diode were found to be compatible with each other.

Effect of Al Concentration on Structural, Optical and Electrical Properties of (Gd, Al) Co-Doped ZnO and Its n-ZnO/p-Si (1 0 0) Heterojunction Structures Prepared via Co-Sputtering Method

Heterojunction structures of n-ZnO/p-Si were prepared through the growth of undoped ZnO and (Gd, Al) co-doped ZnO films onto p-type Si (1 0 0) substrates, using a co-sputtering method. The structural and optical properties of the Gd-doped ZnO films were studied as a function of different Al doping concentrations. The X-ray diffraction profiles indicated that the films had a nanocrystalline structure of ZnO with a (0 0 2) preferential orientation. An increase in the Al doping concentration deteriorated the (0 0 2) diffraction peak intensity. The transmittance measurements in the UV-Vis wavelength range indicated that the film's optical gap increased with increase in Al doping concentration. The heterojunction parameters were evaluated using the current-voltage (I-V) characterization carried out of the fabricated n-ZnO/p-Si heterostructure, in dark conditions at room temperature. From these measurements, the n-ZnO-based DMS/p-Si heterojunction diode with the use of (Gd, Al) co-doped ZnO film showed the lowest leakage current of 1.28 × 10-8 A and an ideality factor η of 1.11, close to the ideal diode behavior of η = 1, compared to the n-Gd-doped ZnO/p-Si and n-undoped ZnO/p-Si heterojunction diodes.