Ideality Factor Research Articles

High-performance and low-power consumption deep UV photodetectors based on MOCVD-grown ZnGa2O4epilayers with high temperature functionality

This work reports on the fabrication of excellent quality deep ultraviolet photodetectors (DUV PDs) based on metalorganic chemical vapor deposition (MOCVD) grown spinel ZnGa2O4 thin films on c-plane sapphire. Herein, The DUV PDs by exhibiting an ultra-low dark current of 6.69 fA and a high photo-to-dark-current ratio (PDCR) of >108 at a low-power operation of 0.2 V. While PDCR reached more than 109 on applied bias of 10 V having extremely low dark current of 37 fA. The detector revealed an ultra-high responsivity of 185 and 3.53 A/W under the exposure of 107 μW/cm2 of 245 nm wavelength at room temperature (RT) and applied bias of 10 and 0.2 V, respectively, and exhibited the record-high detectivity of the order of 1017 Jones. The temperature-dependent operation remained stable across a wide temperature range, from 27 °C to 125 °C, maintaining ultra-low dark current. The nearly constant growth and decay time of DUV PDs throughout the temperature range emphasizes the robustness and reliability of PD. The ideality factor in both DUV and dark conditions nearing unity proves the dominance of the thermionic emission mechanism. Also shows the stable and slight improved performance after a year. Therefore, these findings suggest that ZnGa2O4 is a strong contender for deep UV detection that shows robustness even at high temperatures.

Performance improvement of blue light micro-light emitting diodes (< 20 μm) by neutral beam etching process

In this study, micro-light emitting diodes array (μLEDs) with dimensions of 5 μm and 15 μm chip size were fabricated using Neutral Beam Etching (NBE) processes. Size-dependent issues of μLEDs processed by traditional inductively coupled plasma-reactive ion etching (ICPRIE) were alleviated by NBE technology, which exhibited lower equivalent resistance, turn-on voltage, and Ideality factor as compared with those of μLEDs by ICPRIE. Additionally, higher light output power of μLEDs processed by NBE with both 5 μm and 15 μm resulted in higher EQE 7.6 % and 7.7 % than those of μLEDs processed by ICPRIE. Furthermore, the size effect led to a decrease in EQEmax values of the ICPRIE sample by 0.4 %, but only a 0.1 % decay in NBE. Overall, samples fabricated by the NBE process exhibited superior optoelectronic characteristics. Finally, non-radiative recombination behaviors on the mesa sidewall were verified by cathodoluminescence analysis, showing significant decay in ICPRIE samples but not in NBE samples. These results demonstrated the potential of the NBE process for fabricating small chip sizes blue-light μLEDs required for high-brightness, high-efficiency, and high-resolution μLED displays.

Advancements in P3HT:PCBM solar cells through experimental and simulated techniques

Abstract Organic solar cells are a promising alternative in photovoltaics due to their low manufacturing cost and flexibility. In this study, we developed an organic solar cell of structure (ITO/PEDOT:PSS/P3HT:PCBM/Al) where the active layer is represented by P3HT:PCBM. Experimental studies revealed that this layer has an energy gap of 1.9 eV and a good absorption coefficient of 〖3×10〗^5 〖cm〗^(-1). Using analytical and experimental methods based on (J-V-T) curves, we extracted the key parameters of our device, including parasitic resistances (R_s and R_sh), ideality factor (n), and Schottky potential barrier (ϕ_B) at different temperatures. Also the charge transport mechanism in our junction is identified in this study. We then used simulation to evaluate the performance of our solar cell, obtaining an initial efficiency of 2.13%, in line with experimental results from other research. Our results confirm the feasibility of our theoretical approach, with performance consistent with previous work. However, by introducing an ETL layer (PFN-Br or PDINO), we were able to improve efficiency up to 4.25%. These results highlight the importance of optimising intermediate layers to maximise the efficiency of organic solar cells.

Estimating the productivity of US agriculture: The Fisher total factor productivity index for time series data with unknown prices

AbstractIn this paper, we propose a straightforward way to estimate the Fisher ideal total factor productivity (TFP) index (FI) in cases where price information is unavailable, using ‘shadow prices’ derived from data envelopment analysis (DEA). A Monte Carlo experiment shows that the shadow price Fisher ideal TFP index (SPFI) can effectively estimate the ‘true’ FI with relatively small (and stable) errors. The empirical application to the US agriculture sector (1948–2017) further suggests that the SPFI is a (superior) alternative to the traditional Malmquist DEA, especially in dealing with unbalanced panel or time series data when price data are unknown.

Model Parameters and Degradation Mechanism Analysis of Indium Phosphide Hetero-Junction Bipolar Transistors Exposed to Proton Irradiation

The degradation properties of Indium phosphide hetero-junction bipolar transistors (InP HBTs) under proton irradiation are studied and modelled using a compact model for pre-irradiation, post-irradiation, and post-annealing. The variation rates of the model parameters, such as the base–emitter saturation current (ISE) and ideality factor in the ideal region (NE) in the forward Gummel characteristics, the zero-biased capacitance (Cje) and the grading factor (Mjer) in the BE junction capacitance, and the transit time parameter in the base region (Tfb), are analysed to delve into the degradation mechanism induced by proton irradiation. The displacement damage, induced by proton irradiation in the space charge region of the base–emitter junction and in the quasi-neutral bulk base region, is found to be responsible for the decrease in current gain and cut-off frequency. After annealing, the variation rates of the parameters decrease significantly compared to post-irradiation. This suggests that the recombination of unstable defects leads to a slight recovery in the degradation characteristics of InP HBTs after a period of annealing.

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.

Electrical conduction and photodiode properties of Au/Feq3/p-Si/al hybrid heterostructure

Thin films of iron tris(8-hydroxyquinoline) (Feq3) are prepared on p-Si substrates by thermal deposition under high vacuum. The current-voltage (I–V) curves of Au/Feq3/p-Si/Al heterojunction are recorded as a function of temperature range from 303 to 383 K at 20 K interval. The device shows rectification behavior, with room temperature ideality factor (n) and barrier height (φ) values of 2.30 and 0.81 eV, respectively. The temperature dependence of φ and n is explained in terms of barrier inhomogeneity, in which the homogenous φ value is estimated as 0.97 eV. The conduction mechanisms of the diode are determined and related parameters are evaluated The series resistance of the diode is estimated as a function of temperature. Up on illuminating the diode, the reverse current of the diode increases with increasing the impinging light intensity, from which the photosensitivity and photoconduction are determined.

Fabrication of plasmonic junction diodes based on Ag@ZnO core-shell nanostructures

In this study, Ag nanoparticles and Ag@ZnO core–shell nanostructures were prepared using the wet chemical method and these nanostructures were used for Ag@ZnO/p-Si diode fabrication. Structural, morphological, and optical characterization techniques were applied for Ag@ZnO core–shell NPs prepared by using different molarity of precursor ZnCl2 (10 mM, 20 mM, 30 mM) and showed that the effect of increasing precursor amount on these physical properties of nanoparticles is important. For Ag@ZnO, transmission electron microscopy shows an average diameter of Ag nanoparticles was 51.32 nm and Ag@ZnO core–shell nanostructures were found to be between 31 and 92 nm. The UV-visible absorbance also shows significant plasmonic resonance for NPs, with a slight red shift increasing precursor molarity. The peaks are found to be from 412 nm to 432 nm. This redshift in surface plasmon absorption of Ag@ZnO core–shell structures are consistent with XPS survey. The current–voltage (I-V) characteristic curves of heterojunction diodes were taken in the dark and at room temperature, and it was observed that they showed a rectifying feature. Ideality factor and barrier height values have been found between 2.14 and 3.87, and 0.56 and 0.78, respectively. The results revealed that Ag@ZnO was successfully synthesized and can be used in rectification applications.

Synthesis of 2D yttrium zinc oxide nanosheets via simple chemical route toward high performance Schottky diode based on large charge carriers density and photoresponsivity

Abstract Yttrium zinc oxide (Zn0.85Y0.15O) nanostructures were stoichiometrically prepared by co-precipitation method. XRD, EDX, XPS, SEM, and TEM spectroscopy were examined to investigate structure, composition, and morphological characteristics. The synthesized nanocomposite exhibited polycrystalline structure with small crystallite size ~ 27 nm in which the particles appeared in sheets like shape with high atomic density on surface. The optical parameters including energy gap (Eg) and refractive index (n) were investigated from (T%) and (R%) measurements through wavelength range from 300-900 nm. Al/Y:ZnO/p-Si/Ag Schottky diode was fabricated using thermal evaporating technique and its current-voltage (I-V) was analyzed using different models. The photodiode showed non-ideal behavior with ideality factor greater than unity and small potential barrier. Under various illuminations, the photodiode has revealed high photosensitivity attributed to trapped charge carriers at the interface. The charge carrier density Nd and built-in voltage Vbi were estimated from Mott Schottky (M-S) function suggesting high Schottky diode efficiency.&amp;#xD;

Negative Dielectric Constant in Novel Structure of PA-GO Composite /MnO2/Fe3O4/n-Si

Abstract We present a novel structure of PA-GO composite /MnO2/Fe3O4/n-Si arranged by simple technique and examined by scanning electron microscope, X-ray diffraction, and Raman spectroscopy. The negative dielectric constant appeared for all voltages at frequencies of 103, 102, 10 Hz, proving that the dielectric constant has negative values only at frequencies above one megahertz 106Hz. Also, the dielectric loss has negative values with temperature at all voltages and high frequencies. This structure also has a low dielectric loss tangent from 4 to 50 with all voltages and temperatures and high rectification ratio reach to 1200 times, and high Rj. The performance of dielectric constant, dielectric loss, and dielectric loss tangent depend on the change of frequencies and voltages. The electrical properties of this structure were examined by conventional, dv/dlnI, and the Nord and Cheung method. The ideality factor fluctuates between 3.09 and 3.29, and the barrier height is in the range of 0.56 to 0.58 at room temperature. We found similar results using different methods of measuring the electrical properties. This indicates that the structure is a promising material for preparing diodes, supercapacitor, and high storage devices.

Investigation of hybrid CuPc-doped ZnO/p-silicon photodiodes for photonic and electronic applications

Copper phthalocyanine (CuPc) doped zinc oxide (ZnO) interlayered Al/p-Si Schottky barrier diodes (SBDs) were systematically fabricated utilizing spin coating technique. This study was undertaken to meticulously assess the influence of varying concentrations of CuPc on the intricate electrical and photodiode characteristics of these devices. The investigation involved the characterization of the current–voltage (I–V) characteristics configured with distinct different doping concentrations of CuPc such as 0.05 wt%,1 wt%, 2 wt%, under a wide range of voltages (± 5 V) and illumination irradiances. These measurements enabled the calculation of various critical electrical variables, such as the ideality factor (n), barrier height (ΦB), series resistance (Rs), shunt resistance (Rsh), interface states density (Nss) and their response under various illumination levels (between 10 and 100 mW/cm2) and under dark condition. An increase in the reverse current as the illumination increases suggested the potential utility of these SBDs as photodiodes, photosensors, or photodetectors. Notably, the linear dynamic range (LDR), a crucial factor for image sensors which obtained around 14 for all photodiodes. The photodiodes exhibited a good rectification ratio (RR) of approximately 104. The results obtained indicate that the rectifying properties of the structures can be controlled by CuPc doping. In addition, the results indicated that the presence of CuPc significantly influenced the values of n, ΦB, Rs/Rsh, and Nss. To further analyze the devices, capacitance–voltage (C–V) and conductance–voltage (G–V) measurements were carried out to determine parameters such as diffusion potential (VD), dopant acceptor atoms concentration (NA), Fermi energy level (EF), and width of depletion layer (WD) at both 1 kHz and 1 MHz. The measurements revealed that the capacitance values were higher at low frequencies compared to high frequencies, and this behavior was attributed to Nss. In summary, this study suggests that the manufactured photodiodes have the potential to be employed as photodiodes, sensors, or detectors in optical sensing applications, and their performance can be tailored by adjusting the concentration of CuPc in the ZnO interlayered structures. The discerned outcomes revealed the substantial influence of CuPc concentration on key electrical parameters, with conspicuous trends noted in the values of n, ΦB, Rs/Rsh, and Nss. Furthermore, the observed increase in the reverse current as the illumination level increases highlights the potential utility of these SBDs as sensitive photodiodes/sensors/detectors.

Effect of doping and preparation parameter on AC conductivity and dielectric modulus formalism of Al doped DLC thin films

Here, we report the composite effect of aluminum doping on the dielectric response of Diamond-Like Carbon (DLC) thin films. In addition, the contribution from preparation parameters like acetylene flow rate is also considered to understand sample behavior. AC conductivity study shows the existence of a nonlinear increase of conductivity with frequency leading toward the Jump Relaxation Model (JRM). The transition frequency (ft) is observed, which increases with conductivity. The study reveals that dielectric response is influenced by space charge conductivity, prompting us to adopt the modified Debye law. Deviation from ideal Debye behavior is also confirmed in dielectric modulus analysis. The deviation is frequency-dependent, and a higher deviation is observed in the high-frequency region. Plotting of the Master curve shows the presence of different relaxation dynamics in different samples. A current-voltage (I-V) study of different samples is also undertaken, showing higher values (greater than unity) of the ideality factor.

Photoelectrochemical Properties of Chemical Bath Deposited CdNiSe Thin Films

The chemical bath deposition approach was used to prepare Cd1−xNixSe thin film photoelectrodes on a substrate made of stainless-steel plate. The constructed cell has the configuration: p-CdNiSe | NaOH (1M)+S (1M)+Na2S (1M) | C (graphite). Studying current-voltage characteristics in the dark, capacitance–voltage in the dark, barrier-height measurements, power output, photo response, and spectral response are all part of characterizing the photoelectrochemical cell of the photoelectrodes. For the composition of Cd0.7Ni0.3Se, the junction ideality factor was determined to be minimal. It was discovered that the flat band potential and barrierheight was 710 mV and 0.181 eV respectively. The power output characteristic reveals that, for composition x = 0.3, the short circuit current, open circuit voltage, conversion efficiency and fill factor are respectively, 161 μA/cm2, 260 mV, 0.64% and 48.11%. The greatest current recorded at 725 nm is displayed in the spectral response.

Illumination dependent electrical, photosensitivity and photodetectivity properties of Au/SiO2/n-Si structures: optoelectronic situations

Abstract This study aims to examine the electrical, photosensitivity (S), photo-response (R), and photo-detectivity (D*) properties of Au/SiO2/n-type Si structures under different illumination intensities. The illumination-dependent properties of the Au/SiO2/n-type Si structure with SiO2 interlayer were obtained using current–voltage (I-V) characteristics. The ideality factors (n) and barrier heights (Φbo) values of Au/SiO2/n-type Si structures were obtained and compared from forward and reverse bias current–voltage (I-V) measurements at room temperature. Also, barrier heights (Φbo) and series resistance (R S ) values obtained from Norde method were compared with the values obtained from TE theory. It was observed that ideality factor and barrier height values obtained from forward bias region are higher than the values reverse bias. This means that the linearity or rectification feature in the reverse bias region is better than the forward bias region. Furthermore, photodiode values such as photo response (R), photosensitivity (S) and photodetectivity (D*) of Au/SiO2/n type Si structures were also examined depending on the light intensity. Consequently, the experimental results showed that the increase in reverse current with increasing light indicates that the Au/SiO2/n-type Si structures can be used in semiconductor technology as a photodiode, detector or sensor.

Optoelectronic properties of Au/n-type Si semiconductor structures with SiO2 interlayer

In this study, we investigated the effect of light intensity on electrical and photovoltaic properties using current-voltage (I–V) measurements at room temperature of Au/n-type Si structures with SiO2 interface layer. At each light intensity, the obtained main electrical characteristics such as ideality factors (n), barrier heights (Φbo), rectification ratios (RR), saturation currents (I0) and series resistances (RS) of Au/SiO2/n-type Si structures were calculated from both thermionic emission (TE) and Cheung methods using I–V measurements and compared to each other. Experimental results showed that while the n and I0 values increased with the increase in the light intensity, the Φbo and RR values decreased. While the ideality factor values obtained using the TE method ranged between 1.973 (at dark) and 2.250 (for 100 mW/cm2), these values were obtained between 3.227 and 3.482 using the Cheung method. At the same time, while the barrier height values obtained using the TE method ranged between 0.865 eV (at dark) and 0.817 eV (for 100 mW/cm2), these values were obtained between 0.773 eV and 0.742 eV using the Cheung method. It was observed that while the n values obtained from TE theory were smaller than the values obtained from the Cheung method, the Φbo values were larger than the values obtained from the Cheung function. Furthermore, for the Au/SiO2/n-type Si structures, the photovoltaic parameters such as short circuit current (Isc) and open circuit voltage (Voc) and photocurrent (Iph) were examined under dark, daylight and various light intensities (from 20 to 100 mW/cm2).

Effect of 1 wt% Dimethyl Sulfoxide on the Electrical and Photovoltaic Parameters of Schottky Diodes and Organic Solar Cells Based on PEDOT:PSS

Herein, the electrical conductivity of poly(3,4‐ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS) polymer is improved by adding dimethyl sulfoxide (DMSO) and electrical characterization of the obtained Schottky diode and organic solar cell (OSC) devices are performed from I–V measurements under the light and dark conditions. The scanning electron microscope images of the poly(3‐hexylthiophene):[6,6]‐phenylC61‐butyric acid methylester active layer and PEDOT:PSS layer are obtained. The series resistance (Rs), barrier height (Фb), and ideality factor (n) parameters are obtained from different techniques as a function of light and dark conditions. Furthermore, photovoltaic parameters are calculated for n‐Si/PEDOT:PSS/Au device without DMSO doping and with DMSO doping as a parameter of the light condition and the interface state densities of these devices are obtained for light and dark conditions. DMSO organic solvent improves the short‐circuit current density (Isc), power convert efficiency (or η), open circuit‐voltage (Voc), shunt resistance (Rsh), and series resistance (Rs) values of OSCs. In summary, DMSO solvent rearranges the conductive of PEDOT:PSS, decreases the work function of this conductive polymer (≈5 eV), decreases energy loss in the charge transportation, and increases photovoltaic parameters of Schottky barrier diode and OSC devices.

Comparative Study on Schottky Contact Behaviors between Ga- and N-Polar GaN with SiNx Interlayer

We conducted a comparative study on the characterization of Ga-polar and N-polar GaN metal–insulator–semiconductor (MIS) Schottky contact with a SiNx gate dielectric. The correlation between the surface morphology and the current–voltage (I–V) characteristics of the Ga- and N-polar GaN Schottky contact with and without SiNx was established. The insertion of SiNx helps in reducing the reverse leakage current for both structures, even though the leakage is still higher for N-polar GaN, consistent with the Schottky barrier height calculated using X-ray photoelectron spectroscopy. To optimize the electric property of the N-polar device, various substrate misorientation angles were adopted. Among the different misorientation angles of the sapphire substrate, the GaN MIS Schottky barrier diode grown on 1° sapphire shows the lowest reverse leakage current, the smoothest surface morphology, and the best crystalline quality compared to N-polar GaN grown on 0.2° and 2° sapphire substrates. Furthermore, the mechanism of the reverse leakage current of the MIS-type N-polar GaN Schottky contact was investigated by temperature-dependent I–V characterization. FP emissions are thought to be the dominant reverse conduction mechanism for the N-polar GaN MIS diode. This work provides a promising approach towards the optimization of N-polar electronic devices with low levels of leakage and a favorable ideality factor.

A biomimetic approach to modulating the sustained release of fibroblast growth factor 2 from fibrin microthread scaffolds

Aim: The pleiotropic effect of fibroblast growth factor 2 (FGF2) on promoting myogenesis, angiogenesis, and innervation makes it an ideal growth factor for treating volumetric muscle loss (VML) injuries. While an initial delivery of FGF2 has demonstrated enhanced regenerative potential, the sustained delivery of FGF2 from scaffolds with robust structural properties as well as biophysical and biochemical signaling cues has yet to be explored for treating VML. The goal of this study is to develop an instructive fibrin microthread scaffold with intrinsic topographic alignment cues as well as regenerative signaling cues and a physiologically relevant, sustained release of FGF2 to direct myogenesis and ultimately enhance functional muscle regeneration. Methods: Heparin was passively adsorbed or carbodiimide-conjugated to microthreads, creating a biomimetic binding strategy, mimicking FGF2 sequestration in the extracellular matrix (ECM). It was also evaluated whether FGF2 incorporated into fibrin microthreads would yield sustained release. It was hypothesized that heparin-conjugated and co-incorporated (co-inc) fibrin microthreads would facilitate sustained release of FGF2 from the scaffold and enhance in vitro myoblast proliferation and outgrowth. Results: Toluidine blue staining and Fourier transform infrared spectroscopy confirmed that carbodiimide-conjugated heparin bound to fibrin microthreads in a dose-dependent manner. Release kinetics revealed that heparin-conjugated fibrin microthreads exhibited sustained release of FGF2 over a period of one week. An in vitro assay demonstrated that FGF2 released from microthreads remained bioactive, stimulating myoblast proliferation over four days. Finally, a cellular outgrowth assay suggests that FGF2 promotes increased outgrowth onto microthreads. Conclusions: It was anticipated that the combined effects of fibrin microthread structural properties, topographic alignment cues, and FGF2 release profiles will facilitate the fabrication of a biomimetic scaffold that enhances the regeneration of functional muscle tissue for the treatment of VML injuries.

Investigation of cryogenic current–voltage anomalies in SiGe HBTs: Role of base–emitter junction inhomogeneities

The deviations of cryogenic collector current–voltage characteristics of SiGe heterojunction bipolar transistors (HBTs) from ideal drift-diffusion theory have been a topic of investigation for many years. Recent work indicates that direct tunneling across the base contributes to the non-ideal current in highly scaled devices. However, cryogenic discrepancies have been observed even in older-generation devices for which direct tunneling is negligible, suggesting that another mechanism may also contribute. Although similar non-ideal current–voltage characteristics have been observed in Schottky junctions and were attributed to a spatially inhomogeneous junction potential, this explanation has not been considered for SiGe HBTs. Here, we experimentally investigate this hypothesis by characterizing the collector current ideality factor and built-in potential of a SiGe HBT vs temperature using a cryogenic probe station. The temperature dependence of the ideality factor and the relation between the built-in potential as measured by capacitance–voltage and current–voltage characteristics are in good qualitative agreement with the predictions of a theory of electrical transport across a spatially inhomogeneous junction. These observations suggest that inhomogeneities in the base–emitter junction potential may contribute to the cryogenic non-idealities. This work helps to identify the physical mechanisms limiting the cryogenic microwave noise performance of SiGe HBTs.

Forward leakage currents in GaN p-i-n diodes

Excessive forward leakage currents in GaN p-i-n diodes were investigated. Traditional diffusion mechanism dominates at VF > 2 V. The effective band gap is derived to be ∼2.21 eV, which is much lower than 3.4 eV and attributed to a band fluctuation caused by dislocations; At 1.35 V < VF < 2 V, a trap-assisted tunneling process becomes important, whose ideality factor is still larger than 4.1 at T = 400 K; Two distinct power-law relationships were observed at lower biases, separated at VF = 0.8 V, whose exponents are extracted to be ∼8 and ∼4, respectively. The behavior is in a good agreement with the space-charge-limited model, featuring an exponentially decaying distribution of trap states below the conduction band.