Ideality Factor Research Articles

Space charge limited current in 4H-SiC Schottky diodes in the presence of stacking faults

The presence of crystallographic defects can induce notable effects on the mechanisms ruling the current transport in metal/semiconductor contacts. In this context, in this Letter, the impact of stacking faults (SFs) on the characteristics of 4H-SiC Schottky diodes was investigated under both forward and reverse bias. In particular, in the presence of SFs under the contact, while no significant effect on the ideality factor and barrier height was observed under forward bias, an anomalous increase in the leakage current occurred under reverse bias. The observed behavior of the leakage current could be explained by a space-charge limited current model, consistent with the presence of a distribution of trapping states in the gap of 4H-SiC. An increase in the reverse bias above 30 V leads to a complete trap filling. The weak temperature-dependence of the leakage current observed in this regime suggests the coexistence with a tunneling of the carriers through the barrier. The results can be useful to understand unexpected failures in 4H-SiC Schottky diodes.

Conduction mechanism of Schottky contacts fabricated on etch pits originating from single threading dislocation in a highly Si-doped HVPE GaN substrate

This paper reports the relationship between a single dislocation structure and current leakage mechanism observed in a Pt/n+-GaN Schottky contacts with the combined use of transmission electron microscopy (TEM) and conductive atomic force microscopy (C-AFM). The contacts were fabricated on a substrate grown by hydride vapor phase epitaxy. TEM analysis clarified that large- and small-size etch pits are attributed to mixed/screw and edge dislocations, respectively. Schottky contacts formed on the surfaces of large and small etch pits (L-EPC, S-EPC), a dislocation-free flat area (FLAT), and a Schottky barrier diode with a diameter of 50 μm (SBD) were prepared and their temperature-dependent current-voltage characteristics were measured using C-AFM. Analysis of the forward bias characteristics revealed that the Schottky barrier height increased and the ideality factor approached unity with increasing temperature. Such temperature dependence of the barrier height was well explained by barrier inhomogeneity at the metal/semiconductor interface. From the analysis of the reverse bias characteristics, we found that field emission (FE) currents caused by the high donor concentration of the sample were the dominant conduction mechanism for S-EPC and FLAT. On the other hand, for L-EPC, the FE currents were overlapped by Poole-Frenkel emission (PFE) currents. For SBD, the leakage currents were successfully explained by the FE and thermionic field emission (TFE) mechanisms by assuming dislocation regions with a lowered barrier height. These findings suggest that mixed dislocations are associated with PFE and lower the Schottky barrier.

In-depth opto-electrical analysis of Ni:CdS film towards the performance as Ag/Ni:CdS/FTO Schottky diode

Nickel doped cadmium sulfide (Ni:CdS) thin films are deposited onto glass and FTO substrate using spray pyrolysis technique. The effect of annealing temperature on the thin films and its morphological, microstructural, optical dispersion, linear-nonlinear and electrical, properties are extensively investigated by using various techniques such as field emission scanning electron microscope (FESEM) and atomic force microscopy (AFM), X-ray diffraction (XRD) and ultraviolet visible (UV-VIS) diffuse reflectance spectroscopy. Morphological studies revealed that doped thin films surface is almost homogeneous and well-covered. Peaks associated with Ni, Cd and S elements are present in EDS analysis, which confirm the composition of the films. The energy band calculation using the Tauc plot from the recorded absorption spectra reveals the decrement in the energy gap from 3.75 eV to 3.61 eV and the refractive index is in the range of 2.57–2.62. The effect of annealing temperature on complex dielectric constant are also analyzed. Moreover, the dispersion of refractive index is calculated in terms of Wemple-DiDomenico approach. Third order susceptibility and nonlinear refractive index are calculated of Ni:CdS films. The designed Ag/Ni:CdS/FTO Schottky diode is tested under illumination conditions, and the empirical diode parameters, viz. ideality factor, barrier height, series resistance etc. are influenced by annealing temperature.

Elucidating the Role of Chalcogenide‐Based Interface Passivators in Enhancing the Stability of Perovskite Solar Cells

AbstractChalcogenide‐based Lewis bases are widely used in perovskite solar cells (PSCs) due to their effectiveness in passivating Pb2+ and Pb0‐related defects. However, the underlying principles governing their defect passivation and the relative efficacy of different chalcogen elements remain poorly understood. This study evaluates the effectiveness of oxygen, sulfur, and selenium‐based interface passivator molecules in enhancing the stability and power conversion efficiency (PCE) of perovskite solar cell devices. The hard and soft acid and base (HSAB) principle has been utilized here to gain insights into the defect passivation behavior of chalcogenide‐based molecules. The photoluminescence, ideality factor, and trap density measurements reveal that the sulfide and selenide‐passivated devices exhibit superior defect passivation compared to the oxide‐passivated control device. In terms of stability, the average T75 lifetime (time at which 75% of the initial PCE is retained) of the oxide, sulfide, and selenide passivated samples is 6%, 30%, and 50% higher compared to their un‐passivated counterparts. This enhanced stability with the sulfide and selenide‐based passivators can be attributed to their soft Lewis base nature, which resulted in stronger interaction with the Pb‐related defects, as evidenced by the density‐functional theory calculations and X‐Ray photoelectron spectroscopy study.

Investigation of fundamental electrical and optoelectronic properties of an organic- and carbon-based MnPc/GC photodiode with high photosensitivity

The aim of this work is to provide an alternative to optoelectronic devices that use carbon and organic materials. To achieve this, we coated a modified MnPc organic semiconductor compound onto a graphite-like carbon (GC) thin film using the thermal evaporation technique, and fabricated an organic-based, highly light-sensitive MnPc/GC hybrid heterojunction. The heterojunction had a transmittance of approximately 60% in the visible region, an absorption coefficient of ∼106 m−1, and an energy band gap of 2.6 eV. Subsequently, Ag contacts were grown on the surface of each layer, and the Ag/MnPc/GC/Ag photodiode was subjected to fundamental electrical analysis at various light intensities and a ±3 V applied potential. Analysis in a dark environment revealed that the photodiode had a rectification ratio of 2.59 × 103, a series resistance of 28 Ω, and a shunt resistance of 4.17 × 104 Ω, as calculated from Ohm’s law. The diode ideality factor and barrier height of the photodiode were determined from thermionic emission theory to be 5.60 and 0.71 eV, respectively, and it was observed that these decreased with increasing light intensity. The photodetector parameters of the MnPc/GC hybrid photodiode were determined under positive and negative applied potentials at various light intensities. The highest photocurrent, photoconductive responsivity, photosensitivity, and specific detectivity were determined to be 1.512 × 10−1 A, 11.52 A.W−1, 9.83 × 105, and 2.48 × 1012 Jones, respectively, which were significantly higher than those reported in literature for organic and inorganic-based photodiodes. Based on the findings, it was concluded that the Ag/MnPc/GC/Ag photodiode holds promise as an alternative for sensors, solar cells, photodetectors, and optoelectronic communications applications.

SnF2‐Doped Cs2SnI6 Ordered Vacancy Double Perovskite for Photovoltaic Applications

Air‐stable p‐type SnF2:Cs2SnI6 with a bandgap of 1.6 eV has been demonstrated as a promising material for Pb‐free halide perovskite solar cells. Crystalline Cs2SnI6 phase is obtained with CsI, SnI2, and SnF2 salts in gamma‐butyrolactone solvent, but not with dimethyl sulfoxide and N,N‐dimethylformamide solvents. Cs2SnI6 is found to be stable for at least 1000 h at 100 °C when dark annealed in nitrogen atmosphere. In this study, Cs2SnI6 has been used in a superstrate n–i–p planar device structure enabled by a spin‐coated absorber thickness of ≈2 μm on a chemical bath deposited Zn(O,S) electron transport layer. The best device power conversion efficiency reported here is 5.18% with VOC of 0.81 V, 9.28 mA cm−2 JSC, and 68% fill factor. The dark saturation current and diode ideality factor are estimated as 1.5 × 10−3 mA cm−2 and 2.18, respectively. The devices exhibit a high VOC deficit and low short‐circuit current density due to high bulk and interface recombination. Device efficiency can be expected to increase with improvement in material and interface quality, charge transport, and device engineering.

Optimization, design and size effect on the performance of Ag/CdS:Cu/FTO/glass based Schottky diode

Influences of annealing on optical properties of spray pyrolysis deposited Cu-doped CdS (CdS:Cu) thin-films are investigated and designed Ag/CdS:Cu/FTO/glass based Schottky diode performances are discussed in detail. The sizes of the thin film are estimated through field-emission scanning electron microscopy (FESEM) images, exhibited that the films are composed of different-size, which increases with increasing the annealing temperature. The band-gap decreases from 2.79 eV to 2.75 eV with incresing annealing temperatures. According to I–V measurement, the ideality factor (η), potential height (φh) and series resistance (Rh) of Ag/CdS:Cu/FTO/glass Schottky diodes are estimated by various methods like thermionic-emission, Cheung and Norde, these all methods are consistent well. The ideality-factor and series-resistance decrease with increasing temperature and size. When the CdS:Cu thin-films are annealed at 400°C, the Ag/CdS:Cu Schottky diodes have good rectifying behaviors with an ideality-factor of 4.67–5.03, a Schottky-potential height of 0.98 eV–0.87 eV and relatively low series-resistance of 2.35kΩ-3.12kΩ. The present study will give a better understanding and insight into the Ag/CdS:Cu/FTO/glass Schottky junction.

Doping GaN NPs Synthesized by a Chemical Method for p-n Junction Application

This research was devoted to studying the doping of GaN NPs at low temperature with Mg and the possibility of using them in the p-n junction. This study was subjected to a FESEM, EDX, XRD, PL and Hall Effect examination. The FESEM examination showed clear images of the NPs, the XRD peaks appear at 2? = 32.5, 39.1 and 45.48 which conform the crystalline of p-GaN NPs, Hole Effects measurements confirm the p-GaN with different Mg ratios. The ideality factor and series resistance of p-n junction have been measured.

Long-term stability of graphene/c-Si Schottky-junction solar cells

A long operational lifetime is required for the use of solar cells in real-life photovoltaic applications. The optimization of operational lifetimes is achieved through understanding the inherent degradation phenomena in solar cells. In this study, graphene/Si Schottky-junction solar cells were produced, utilizing liquid-phase-exfoliated graphene as an active surface. The operational and interface stability of these solar cells over a period of 5 years in ambient conditions (following ISOS-D protocols: dark storage/shelf life) was examined, and the origin of their degradation was reported. It was found that the dominant degradation mechanism could be attributed to the degradation of silver contacts. This was indicated by a decrease in shunt resistance, an increase in the ideality factor (due to a higher carrier recombination), and a constant defect density in graphene films for up to 4 years. Measurements across the solar cell's active area during the 5-year period revealed neither significant spatial inhomogeneity, nor shunt channel defects.

Efficiency-loss analysis of monolithic perovskite/silicon tandem solar cells by identifying the patterns of a dual two-diode model’s current-voltage curves

In this work, we developed a simple and direct circuit model with a dual two-diode model that can be solved by a SPICE numerical simulation to comprehensively describe the monolithic perovskite/crystalline silicon (PVS/c-Si) tandem solar cells. We are able to reveal the effects of different efficiency-loss mechanisms based on the illuminated current density-voltage (J-V), semi-log dark J-V, and local ideality factor (m-V) curves. The effects of the individual efficiency-loss mechanism on the tandem cell’s efficiency are discussed, including the exp(V/V T) and exp(V/2V T) recombination, the whole cell’s and subcell’s shunts, and the Ohmic-contact or Schottky-contact of the intermediate junction. We can also fit a practical J-V curve and find a specific group of parameters by the trial-and-error method. Although the fitted parameters are not a unique solution, they are valuable clues for identifying the efficiency loss with the aid of the cell’s structure and experimental processes. This method can also serve as an open platform for analyzing other tandem solar cells by substituting the corresponding circuit models. In summary, we developed a simple and effective methodology to diagnose the efficiency-loss source of a monolithic PVS/c-Si tandem cell, which is helpful to researchers who wish to adopt the proper approaches to improve their solar cells.

Work function modulation and charge transport studies of 100 MeV Au7+ ions irradiated TiO2 films for optoelectronic devices

This work demonstrates the impact of 100 MeV Au7+ ion irradiation on the work function and charge-transport properties of TiO2 thin films. The sol-gel synthesized TiO2 films were irradiated by 100 MeV Au7+ ions with varying fluences from 1 × 1011 ion-cm−2 to 1 × 1013 ion-cm−2. The surface potential of these films is found to vary from 139 mV to 469 mV for pristine to ion-irradiated TiO2 thin films. This alternatively tuned the work function of the TiO2 films from −4.87 eV to −4.53 eV which may be due to the higher oxygen vacancies and surface defects created by ion irradiation. The optical transmittance and band gap of the TiO2 thin films are found to be increased after ion irradiation. Photoluminescence and Raman measurements illustrate that various irradiation-induced defect levels such as self-trapped states, oxygen vacancies, color centers, and deep-level emission defects have altered in TiO2 films after ion irradiation. Further, important electrical parameters such as the Schottky barrier height, sheet resistance, and ideality factor have been evaluated to understand the impact of ion irradiation on the charge carrier transport properties of TiO2 films by fabricating the diode in the device configuration FTO/TiO2/Ag.

A study on investigation of electrical properties of Au/Chlorophyll-a/n-Si/Al structure

The chlorophyll-a (Chl-a) thin film has been formed on the n-Si substrate using a spin-coater. The electrical properties of the Au/Chl-a/n-Si/Al structure have been examined with the data obtained from the current–voltage (I–V) measurements in the dark and under illumination at room temperature. The ideality factor (n) and barrier height (Φb) values have been calculated as 1.24 and 0.799 eV in the dark and 1.08 and 0.824 eV in daylight at room temperature. Also, I–V measurements were taken under different illuminations, and some photoelectrical parameters of the Au/Chl-a/n-Si/Al structure, such as photocurrent, photosensitivity, and Ion/Ioff, were investigated. The results show that the Chl-a thin film can be utilized to fabricate photodiodes and solar cells.

Optoelectronic enhancement of ZnO/p-Si Schottky barrier photodiodes by (Sn,Ti) co-doping

In this study, metal–semiconductor–metal (MSM) ZnO-based Schottky barrier diodes (SBDs) were fabricated on the basis of titanium-doped tin–zinc oxide (SZT) films by sol–gel spin coating. Au/(Sn:Zn):Ti:ZnO/p-Si/Au SBDs with varying wt% of Ti were then fabricated. The effects of Ti doping concentration on the structural, optical, and electrical properties were studied. The doped films are consistently homogeneous with increasing Ti content. The optical measurements confirm high film transmittance in the visible spectrum. The optical band gap energy of the SZT films was around 3.90 ± 0.02 eV. The current–voltage, impedance spectroscopic, and photoresponse measurements showed that Ti-doping improved the performance of the devices by increasing the barrier heights and hence the rectification ratios of the devices. The reduction in ideality factors and series resistances implies that Ti doping improves the devices towards near-ideal behavior by passivating interface states.

Improvement in conductivity of lead-free CH3NH3SnI3 perovskite thin film using multi-walled carbon nanotubes as a transporter

CH3NH3SnI3 is a lead-free perovskite material that gains significant attention due to its favourable properties for optoelectronic device applications. It is a potential replacement for lead-based perovskite materials. However, the presence of traps, defects, and oxidation vacancies within these perovskite-based devices hinders the flow of charge carriers, causing them to become trapped or recombined within the device before reaching the electrodes. This limits the electrical performance of the device. To address this issue, this study focuses on improving the electrical performance of CH3NH3SnI3 perovskite by incorporating MWCNTs. Thin films of CH3NH3SnI3 perovskite were prepared both with and without MWCNTs. By employing the Van der Pauw method, resistivity measurements revealed that the electrical conductivity of the film increased to 7.80 × 10−2 S/m with the presence of MWCNTs, compared to 8.4 × 10−4 S/m without them. I-V measurements of the thin films-based Schottky devices showed that the conductivity increased from 1.21 × 10−5 S/m to 1.02 × 10−4 S/m with MWCNTs, while the barrier height decreased from 0.51 eV to 0.43 eV, and the ideality factor decreased from 4.01 to 2.56. The improved electrical performance observed when MWCNTs were incorporated, suggested that they formed a charge transfer pathway for carriers within the perovskite material. This pathway reduced trap energy, enabling charge carriers to percolate between grains and reach the electrodes. These findings highlight the significance of MWCNTs as a means to enhance the charge transfer dynamics in environmentally friendly CH3NH3SnI3 perovskite-based devices. Such improvements have promising implications for the development of future perovskite-based devices.

AgSbTe2 semi-nanocrystalline thin films as a multifunctional platform for optoelectronic and diode applications

The synthesis of the nanosized multifunctional thin film provides new solutions for many technological issues and consider a great step for miniaturized technology. Toward these goals, AgSbTe2 semi-nanocrystalline thin films of different thicknesses were synthesized by the thermal evaporation technique. The structural features were investigated by X-ray diffraction, and selected area electron diffraction (SAED) yielding a semi-nanocrystalline thin film of grain size ranging from 9.98 to 21.38 nm. The energy-dispersive X-ray spectroscopy (EDAX) verified the high purity and stoichiometry of the deposited films. For optoelectronic application, many optical parameters, including band gap (Eg), Urbach energy (Eu), Refractive index (n), dispersion energy (Ed), electronic polarizability (αe), and interband transition strength (JCV) were extensively discussed. The optical band gap reduced from 1.41 to 1.04 eV upon increasing the thickness from 150 to 550 nm. The temperature dependence of the electrical resistivity (ρ) of nanosized thin film was measured and the activation energy was estimated and it was found that the resistivity increased up to 450 K asserting the semiconductor behavior of the films. As for diode application, The Ag/2D-MoS2/p-AgSbTe2 (550 nm)/n-Si/Al heterostructure diode was constructed by thermal evaporation and all the diode parameters alongside conduction mechanism were studied in detail. AgSbTe2-based diode showed a low rectification ratio; however, the ideality factor (n) and zero bias barrier height (Φb) had optimal values of about 1.40 and 0.75 at room temperature, respectively.

Transparent p-n heterojunction thin film diodes based on p-CuCrO2 and n-In2O3

Design and realization of high-performance transparent p-n heterojunctions are needed for the development of transparent electronic technology. In this study, we report the rectification behavior of transparent p-n heterojunctions based on solution-processed p-type CuCrO2 and n-type In2O3 thin films. The performance of heterojunction is improved by changing the annealing temperature of In2O3 thin film. The optimized p-n diode shows high rectification rate of 1.41 × 104 (at ± 3 V) and an ideal factor of 3.9 while maintain visible transmittance exceeding 60%. The conduction mechanism is dominated by space-charge limited conduction in the heterojunction. The results will give impetus to the application of delafossite oxide-based diodes in transparent electronics.

Molecular design of ferrocene-based novel polymer using click chemistry via chemoselective polymerization and investigation of electrical properties as organic Schottky diode

Organic Schottky diodes are electronic devices that consist of a metal–semiconductor junction formed with an organic polymer as the semiconductor material. This work synthesized cinnamic acid side chain bearing polymer and its ferrocene-modified polymer. Thermal stability, dielectric and electrical properties of the initial polymer and the modified one were examined and the addition of a ferrocene unit to the initial polymer clearly improved the optical and electrical properties of the target polymer. Due to the influence of ferrocene, the dielectric constant increased from 8.69 to 18.92. Additionally, it was discovered that the ac conductivity value raised from 6.40x10−9 to 2.64x10−8. The Al/modified-polymer/p-Si structure exhibits an ideality factor of 2.22, a barrier height of 0.61 eV, and a reverse bias current of 1.28 10−5 A in the dark, according to the I-V measurements. These results demonstrated the fabricated diodes have a rectifier behavior. This diode exhibits unique electrical properties due to the characteristics of the organic polymer.

Ultra-low turn-on voltage quasi-vertical GaN Schottky barrier diode with homogeneous barrier height

Quasi-vertical Schottky Barrier Diodes (SBDs) with near to ideal turn-on voltage and ideality factor (n) of 1.02, were fabricated on a GaN on Si substrate. The average turn-on voltage and on-resistance values were found to be 0.23 ± 0.005 V (at 1 A/cm2) and 1.76 ± 0.11 mΩcm2, respectively with diode series resistance of 11 Ω. The analysis of the current–voltage curve revealed a temperature-independent barrier height, however the capacitance–voltage method showed a negative temperature coefficient. This discrepancy is discussed in the paper. Variable range hopping through dislocations is shown to be the dominant reverse current leakage mechanisms identified in the fabricated diode, with a characteristic temperature, T0 of 2 × 1010 K.

Analysis of temperature dependent current-voltage and frequency dependent capacitance-voltage characteristics of Au/CoO/p-Si/Al MIS diode

In this study, the production and electrical characterization of Schottky circuit elements of Au/CoO/p-Si/Al (MIS) structure were investigated. Diode parameters such as the ideality factor (n), barrier height (Φb) and series resistance of Au/CoO/p-Si/Al structures were calculated from the forward bias I-V characteristics of the diode using the different methods such as Thermionic Emission method (TE), Cheung functions and Norde method. The variations of diode parameters from I-V measurements depending on the temperature were examined. In addition, diffusion potential (Vd), barrier height (Φb), Fermi energy level (Ef) and free carrier concentration (Na) were calculated from the C-V measurements of the diode. The variations of these values with frequency were examined from the C-V measurements.

Voltage-margin limiting mechanisms of AlScN-based HEMTs

In this work, the off-state characteristics of AlScN/GaN high electron mobility transistors (HEMTs) grown by metalorganic chemical vapor deposition (MOCVD) were studied and directly compared to an AlGaN- and an AlN-HEMT grown in the same MOCVD. Pinch-off instability and leaky capacitive measurements were observed for AlScN-based HEMTs, which was correlated with a higher ideality factor and lower effective potential barrier height than the AlGaN and AlN-HEMTs. However, the reverse bias characteristics exhibited a sudden drain-current increase without a significant increase in gate-leakage current. The drain-leakage current is assumed to be related to a parasitic channel across the AlScN-barrier as a result of trap-assisted carrier transport with a Poole–Frenkel characteristic. The demonstrated pinch-off instability led to significant gain expansion in load-pull measurements and early soft-breakdown, which, in turn, limits the achievable voltage-margin. The results demonstrate a key issue to reveal the full potential of AlScN-based HEMTs for mm-wave applications.