High Ideality Factor Research Articles

Epilayer thickness effect on the electrical and breakdown characteristics of vertical β-Ga2O3 Schottky barrier diode

The current–voltage and breakdown characteristics of Au/Ni/β-Ga2O3 Schottky barrier diodes were investigated as a function of β-Ga2O3 epilayer thickness in the range of 6–19 μm. The X-ray rocking curves indicated that the full-width half-maximum is reduced with increasing epilayer thickness, implying an improvement in the crystallinity of β-Ga2O3 epilayer. The barrier heights of the field-plated β-Ga2O3 Schottky barrier diode with epitaxial layer thickness of 6, 12, and 19 μm were obtained as 1.01, 1.03, and 1.04 eV, with the ideality factor values being 1.21, 1.19, and 1.46, respectively. The higher ideality factors could be associated with the existence of inhomogeneity at the metal–semiconductor interface. The series resistance of the Schottky diode obtained increased with increasing epilayer thickness. The Schottky diode fabricated on 19 μm thick epitaxial layer exhibited a higher breakdown voltage of 490 V. The increase in epilayer thickness led to the widening of depletion region, resulting in lower electric field over a larger distance. This could be a main cause of the enhancement of the breakdown voltage characteristics of β-Ga2O3 Schottky barrier diode.

The influence of oxygen partial pressure on the properties of sputtered vertical NiO/β-Ga2O3 heterojunction diodes

In this work we present studies on the influence of oxygen partial pressure on the properties of sputtered vertical NiO/β-Ga2O3 heterojunction diodes. Obtained results shows substantial effect of oxygen partial pressure on the electrical properties of NiO/β-Ga2O3 heterojunction diodes. The diodes with NiO layers deposited in pure Ar shows Schottky-like I-V characteristics with low ideality factor of 1.05 and barrier height of 1.27 eV as well as low turn-on voltage close to 1V. On the other hand, diodes with NiO layer deposited in oxygen containing atmosphere shows typical p-n diode characteristics. The best electrical characteristics i.e. low on-state resistance of 2.85 mΩcm2, lack of defects and low ideality factor down to 1.07 at RT along with high breakdown voltage close to 900V without any junction termination, were obtained for diodes with NiO layers deposited at 50 % oxygen content. We have demonstrated that by optimization of oxygen partial pressure, the properties of NiO/β-Ga2O3 heterojunction diodes can be tuned and excellent electrical performance in terms of low-on state resistance, high breakdown voltage, low-leakage current and low ideality factor, can be obtained.

Influence of material properties of liquid absorption filters for concentrated photovoltaic/thermal hybrid systems

A concentrated photovoltaic/thermal system with a liquid filter is an effective technique to utilize the whole solar spectrum for power production. However, fundamental issues still need further investigation, including the structure of flow design and absorptive fluid selection principles. This paper presents a comparative study of optimized configurations of fluid flow channels in a concentrated photovoltaic/thermal system. MATLAB was used to study the influence of fluid thermal properties and transmittance on the system performance. The results showed that increasing the ideality factor from 0.5 to 1 can improve the overall exergy efficiencies of the coupled and decoupled concentrated photovoltaic/thermal system by 2.2 % and 2.4 %, respectively. Moreover, it was found that the coupled concentrated photovoltaic/thermal is more suitable for electrical production when the heat capacity exceeds 2500 J/kgK. The coupled system’s outlet temperature is boosted to 20˚C when the ideality factor is decreased by 20 % but requires significantly lower specific heat capacities. Overall energy efficiency tends to be higher at high heat capacity and low ideality factor values, while exergy efficiency tends to be higher at high heat capacity and high ideality factor values.

Role of interfacial layer as PANI–silicene in Si-based photodiodes

Silicene is a 2D monoatomic sheet of silicon and can be used for various applications such as degradation, therapy, and biosafety. Polyaniline (PANI) is a conducting polymer employed for electronic devices. In this study, we synthesized PANI–silicene composites and operated as an external interfacial layer between Al and different type substrates of p-Si and n-Si to compare Schottky-type photodiodes of PANI–silicene/n-Si and PANI–silicene/p-Si. The silicene structures were investigated using X-ray diffractometry (XRD) and scanning electron microscopy (SEM) techniques. Also, the light power intensity dependent of PANI–silicene/n-Si and PANI–silicene/p-Si photodiodes carried out in the range 0–100 mW/cm2 and I–t measurements utilized to determine the response time of the photodiodes. Basic parameters of devices such as ideality factors barrier, height, and series resistance were obtained by Norde and Cheung methods and thermionic emission (TE) theory from I–V graphs. While the PANI–silicene/n-Si exhibited high ideality factor values of 5.49, the PANI–silicene/p-Si photodiodes showed a low ideality factor of 1.48. The photodiode parameters such as detectivity and responsivity were calculated as 6.40 × 109 Jones and 38.9 mA/W for n-Si substrate and 78.2 mA/W and 8.81 × 109 Jones for p-Si substrate. The case of basic electrical properties for PANI–silicene composite interlayer-based photodiodes was analyzed in detail.

Competition between Transport and Recombination in Dye Solar Cells at Low Light Intensity

The efficiency of electron collection in a dye‐sensitized solar cell (DSC) is determined by a delicate balance between electronic transport and recombination losses caused by electron transfer to dye cations and electron acceptors. While state‐of‐the‐art DSCs have demonstrated quantitative electron collection under standard 1 sun conditions, the nonlinear nature of the trapping/detrapping dynamics in the photoanode with respect to the stored electronic charge can result in suboptimal performance under the low illumination intensity conditions commonly found indoors. Herein, the key factors influencing electron collection in relation to light intensity using impedance spectroscopy and numerical analysis are thoroughly examined. Impedance analysis reveals that the electron diffusion length tends to decrease as the quasi‐Fermi level is lowered, approaching the critical limit (Ln/d ≈ 1) at intensities characteristic of indoor illumination. A range of tert‐butyl pyridine concentrations and different thermal and chemical treatments of the TiO2 are tested, showing that this low intensity limitation is inherent to the multiple‐trapping mechanism that governs the functioning of a DSC. It is concluded that relatively high ideality factors, nonoptimal electrolyte compositions, or small variations in the quality of the TiO2 layer can result in electron collection limitations that are not apparent under 1 sun but become noticeable at low light intensities.

Trap-assisted monolayer ReSe2/Si heterojunction with high photoconductive gain and self-driven broadband photodetector.

The development of photodetectors is crucial in fields such as optical communication, image sensing, medical devices and military equipment, where high sensitivity is paramount. We fabricated an ambipolar photodiode using monolayer triclinic ReSe2, synthesized by chemical vapor deposition on p-type Si substrate. The photodetector has a broadband response range from 405 to 1100 nm. The device exhibits high sensitivity to NIR radiation with a high Iph/Idark (ON/OFF) ratio of 5.8 × 104, responsivity (R) of 465 A/W, and specific detectivity (D) of 4.8 × 1013 Jones at open circuit voltage (Voc), indicating photovoltaic behavior. Our ReSe2/Si heterojunction photodetector also exhibits low dark current of 1.4 × 10-9 A and high external quantum efficiency (EQE) of 54368.2% for 1060 nm at -3 V, demonstrating a photoconductive gain. The maximum responsivity (R = 465 A/W) can be achieved at -3 V reverse bias under 1060 nm. The device has a high ideality factor (4.8) and power coefficient (α = 0.5), indicating the presence of interface and sub-gap states that enhance device responsivity at lower illumination intensities by re-exciting trapped carriers into the conduction band. Our results offer important insights into the underlying photo-physics of the ReSe2/Si heterojunction and propose promising avenues for developing advanced broadband photodetectors of high performance.

Spray pyrolyzed lead oxide films for Schottky junction solar cells

In this paper, we report the fabrication of Schottky solar cell based on spray pyrolysed lead oxide semiconductor thin films. The non-linear junction were created by using high work function metal alloy of Au–Pd with hydrogen treated undoped and Indium doped lead oxide films. The output of Schottky device with different thickness of absorber layer is presented. The electrical parameters of the device are ascertained from the I–V measurements. The device with 2 μm thickness of absorber layer gives a Voc value of 148 mV and Jsc value of 0.21 mA/cm2. The high ideality factor obtained for all varying thickness is attributed to both the surface states generated under illumination and non-homogeneous interface due to the rough surfaces of spray pyrolysed films. In case of Indium doped lead oxide films, an enhanced Voc value of 570 mV and Jsc of 0.11 mA/cm2 is observed. The pristine films and doped films have been characterized by X-Ray diffraction, Raman spectroscopy and scanning electron microscopy.

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.

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.

Extremely high frequency Schottky diodes based on single GaN nanowires

Gallium nitride (GaN) is one of the most promising materials for high-frequency devices owing to its prominent material properties. We report on the fabrication and study of a series of Schottky diodes in the ground-signal-ground topology based on individual GaN nanowires. The electrical characterization of I–V curves demonstrated relatively high ideality factor value (about 6–9) in comparison to the planar Au/GaN diodes that can be attributed to the nanowire geometry. The effective barrier height in the studied structures was defined in the range of 0.25–0.4 eV. The small-signal frequency analysis was employed to study the dependency of the scattering parameters in the broad range from 0.1 to 40 GHz. The approximation fitting of the experimental data indicated the record high cutoff frequency of about 165.8 GHz.

Bias dependent NDR in TiO2/NiO heterojunction diodes

TiO2/NiO thin film heterojunction diodes are fabricated using electron beam evaporation and DC sputtering techniques. Three different thicknesses of NiO (58, 82, and 160 nm) are combined with a TiO2 film of about 80 nm thick. The common device configuration is FTO/TiO2/NiO/Au with a 4 mm sq. device area. The thickness dependent diode I-V characteristics were analyzed; with the increase in thickness, the diode knee voltage, series resistance, and ideality factor have reduced. All the devices exhibit a high diode ideality factor, which means the diode currents are not limited by drift, diffusion, or recombination at the space charge region. The high ideality factor points to the presence of interface states, spatial inhomogeneities, or tunneling in the devices. Further, the bias dependent negative differential resistance (NDR) in I-V characteristics and the presence of an anomalous peak in C-V characteristics were analyzed, which claimed the presence of interfacial trap states, defects, or tunneling in the diodes. The Fowler-Nordheim tunnel model was applied to the devices and the field enhancement factors were calculated as −14.3, −9.3, and −9.2 for the diodes in the increasing order of thickness. The tunneling phenomenon was confirmed as trap-assisted indirect tunneling. Also, the temperature dependence of NDR was studied.

Effect of interfacial native oxide on the IV characteristics of ZnO/Si(111) heterojunction

n-ZnO/p-Si(111) heterojunctions, with and without interfacial oxide layer, have been fabricated by growing Zn thin films on Si(111) substrate via DC Magnetron sputtering followed by oxidation in air at 800 °C. The specimen with and without interfacial oxide layer is referred to as ZnO/Si_RCA and ZnO/Si_HF respectively. Quality of the thin film has been studied using Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). Temperature dependent surface (30 °C - 200 °C) and interfacial (30 °C - 150 ۠°C) current-voltage (T-IV) measurements of both specimens have been studied, under ambient conditions. Surface IV characteristics of ZnO/Si_HF shows lower current response compared to ZnO/Si_RCA. This has been attributed to diffusion of carriers across the junction. ZnO/Si_RCA shows a high ideality factor of 18.9 at 30 °C which decreases to 7.4 at 150 °C. ZnO/Si_HF shows a reduced ideality factor of 11.1 at 30 °C which further decreases to 6.6 at 150 °C.

Estimation of Charge Carrier Density of Turmeric Dye in the Presence of Polyvinyl Alcohol (PVA) and Its Electrical Characterization as Herbal Diode

The study on the semiconducting properties of herbal dye and various parameters of the herbal dye-based device is an important area of research in the coming days. In this work, we have measured the conductivity and Hall coefficient of turmeric dye in solid thin film form. Using the working principle of the Hall Effect, we have measured the Hall coefficient (HC) of this film. It is found that the curves of Hall voltage (VH) –Hall current (HC) and Hall voltage (VH) – Magnetic field (BH) are linear. The Hall coefficient has been estimated from these curves. The average value of the Hall coefficient (R) is 22.64 × 10-4 . The conductivity (σ) of the film is 1.5 10-10 m-1. We have estimated charge carrier density from this parameter, and its typical value is 2.8 23 m-3. We have also prepared a diode using this turmeric dye and extracted reverse saturation current, rectification ratio, ideality factor, series resistance, etc. It has been noticed that the diode exhibits high ideality factor and series resistance. The presence of traps is one of the main reasons for these high values. So, we have also measured the trapped energy of the device considering exponential trap distribution.

Temperature-dependent study on AlGaN-based deep ultraviolet light-emitting diode for the origin of high ideality factor

Deep ultraviolet light-emitting diodes (DUV LEDs) are promising light sources for disinfection, especially during the pandemic of novel coronavirus (COVID-19). Despite much effort in the development of DUV LEDs, the device temperature and ideality factor are key parameters of devices, which are often neglected. Here, we developed a simple and convenient method to study the behavior of a 280 nm AlGaN-based DUV LED, obtaining the electrical, optical, and thermal properties within one measurement. From the experimental results, we find that the light output power and wall-plug efficiency of the AlGaN-based DUV LED are strongly affected by device temperature, ideality factor (β), and series resistance (Rs). β decreases from 9.3 to 8.1 at 40 mA when the temperature increases from 302 to 317 K. We compared these results with simulations and found that the high potential barriers inside the device and the carrier concentration in n-type or p-type layers, especially the hole concentration in p-type layers, are the two key factors for the high value of the ideality factor from the LED structure. As the device temperature increases, carriers with higher energy would overcome some potential barriers and Mg acceptor activation would be more efficient, which are beneficial for carrier transportation. However, these also lead to the carrier overflow and weaken the radiative recombination rate. The trade-off role of device temperature in carriers between transportation and overflow is needed to be considered in the future development of DUV LEDs with higher efficiency and higher brightness.

Effect of various PCBM doping on the interfacial layer of Al/PCBM:ZnO/p-Si photodiodes

The light can be detected by various devices such as photoconductors, photodetectors, phototransistors, solar cells, and photodiodes, and the light can be employed energy harvesting as well as sensing applications. Various materials can be utilized to raising of the efficiency of light-based devices. In this present study, metal–semiconductor (MS) devices with various [6,6]-Phenyl C61-butyric acid methyl ester (PCBM)-doped zinc oxide (ZnO) interfacial layer were fabricated for photodiode applications. Commercially purchased PCBM and ZnO were mixed in order to obtain undoped, 3%, 5%, and 10% PCBM-doped ZnO interfacial layer for Al/PCBM:ZnO/p-Si devices. The obtained solutions were layered on the p-type silicon (p-Si) substrates by spin-coating method. The thermal evaporation technique was utilized to deposit Al metal electrodes both back and front sides. The morphological properties of the fabricated devices were characterized by AFM. The morphological images of the AFM revealed that PCBM doping affected the surface morphology as well as surface roughness of the ZnO layers. I–V measurements were carried out in the dark and under varying illumination conditions for electrical properties. The devices exhibited good rectifying properties at around 103 rates, both dark and various illumination conditions, according to I–V graphs. The junction parameters of the produced devices were determined by using thermionic emission, Norde, and Cheung models from the I–V characteristics of the devices. The devices have high ideality factors, and these values generally fluctuate with varying PCBM-doping amounts. The current transient measurements show that PCBM doping provide increasing in the light response capacity. According to the results, the devices can be employed as photodiode and photodetector applications for the further works in the industry.

Effect of metal contacts on (100) β-Ga2O3 Schottky barriers

The Schottky barriers of Ti, Mo, Co, Ni, Pd, and Au on (100) β-Ga2O3 substrates were analyzed using a combination of current-voltage (J-V), capacitance-voltage (C-V), and current-voltage-temperature (J-V-T) measurements. Near-ideal, average ideality factors for Ti, Mo, Co, and Ni were 1.05–1.15, whereas higher ideality factors (∼1.3) were observed for Pd and Au contacts. Barrier heights ranging from 0.60 to 1.20 eV were calculated from J-V measurements for the metals with low ideality factors. C-V measurements of all Schottky metals were conducted and yielded average barrier heights ranging from 0.78 to 1.98 eV. J-V-T measurements of Ti and Co diodes yielded barrier heights of 0.81 and 1.35 eV, respectively. The results reveal a strong positive correlation between the calculated Schottky barrier heights and the metal work functions: the index of interface behavior, S = 0.70, 0.97, and 0.81 for J-V, C-V, and J-V-T data, respectively.

A review of high ideality factor in gallium nitride-based light-emitting diode

Theory concerning the high ideality factor of gallium nitride (GaN) based light- emitting diode (LED) has been reviewed. The presence of a high ideality factor indicates a large forward voltage that results in efficiency reduction. The paper suggests that tunneling is the main reason defining the exponential behaviour of current-voltage measurements, which leads to a high ideality factor. However, there is also a paper that suggests that the design of current geometry in the LED chip defines the value of ideality factor. An effective current spreading geometry in the LED chip will minimize the ideality factor and make it fall between the ideal range of 1 to 2. Besides, how the ideality factor is calculated will also play a major role in defining its value. By calculating the ideality factor based solely on the radiative recombination current formula, the value of ideality factor can result in an ideal ideality factor of 1.08.

Fabrication and characterization of p-Si/n-In2O3 and p-Si/n-ITO junction diodes for optoelectronic device applications

Octahedral novel indium tin oxide (ITO) films were fabricated on glass substrates. The dopant material tin (Sn) was added at different concentration like 0, 5, 10, 15 weight percentage (wt.%) with indium oxide precursor and the synthesis was done by spray pyrolysis technique. XRD studies revealed proper doping of tin in indium oxide crystal lattice structure. The surface morphology of ITO films confirmed the octahedral structure of crystallites formed and the variation in size of the microstructures with doping concentration. The bonding states of indium and tin with oxygen and composition of ITO films were inspected through XPS. The average roughness of films varied from 26.65 to 139.08 nm. The optical properties studied from UV-VIS studies showed a sharp increase in bandgap from undoped to 5 wt.% Sn doped indium oxide films followed by slight decrease in values with the increase in doping concentration. The photoluminescence excitation of ITO films showed a rapid fall in the peak intensity values due to the quenching of oxygen vacancies and a slight blue shift in emission confirms the doping of tin indium oxide. The resistivity values tremendously decrease with increase in doping concentration, that is tin doping improves conduction which was observed using two probe method. The fabricated p-Si/n-ITO junction diode shows that the ITO is degenerated semiconductor and the photo response is exhibited with a high ideality factor of 8.98 in dark and 6.46 in visible light exposed conditions respectively.

Current--Voltage, Capacitance--Voltage--Temperature, and DLTS Studies of Ni|6H-SiC Schottky Diode

In this paper, we give a systematical description of Ni|6H-SiC Schottky diode by current--voltage I(V) characteristics at room temperature and capacitance--voltage C(V) characteristics at various frequencies (10-800 kHz) and various temperatures (77-350oK). The I(V) characteristics show a double-barrier phenomenon, which gives a low and high barrier height (phiLbn=0.91 eV, phiHbn=1.55 eV), with a difference of Deltaphibn=0.64 eV. Also, low ideality factor nL=1.94 and high ideality factor nH=1.22 are obtained. The C-V-T measurements show that the barrier height phibn decreases with decreasing of temperature and gives a temperature coefficient alpha=1.0·10-3 eV/K and phibn(T=0 K)=1.32 eV. Deep-level transient spectroscopy (DLTS) has been used to investigate deep levels in the Ni|6H-SiC Schottky diode. The traps signatures such as activation energies Ea=0.50±0.07 eV, capture cross-section sigma=1.8·10-20 cm2, and defect concentration NT=6.2·1013 cm-3 were calculated from Arrhenius plots. Keywords: si1licon carbide, Schottky diodes, I-V, C-V-T, deep-level transient spectroscopy (DLTS).

Indium Nanoparticles Capped TiO₂ Nanowire Array for Boosted Photosensing Adoption

The boosted photosensing performances have been reported for Indium (In) nanoparticles (NPs) capped TiO2 nanowire (NW) array using Glancing angle deposition (GLAD) technique. The In NP based photosensor possessed high ideality factor of ~12.8 and the enhancement in photoresponsivity has been also observed. The ON/OFF switching irradiation for the In NPs based photosensor has increased from $4.6~\mu \text{A}$ to $6.2~\mu \text{A}$ and vice versa with a rise time of 0.45 sec and fall time of 0.56 sec.