Forward Bias Region Research Articles

Characterization of an Environmentally Responsive Organic-Inorganic Hybrid Fe3O4/SiO2/PPy-c Core-Shell Nanocomposite with Magneto-Chromatic Ability for Synergistic Electrical Properties.

The aim of this study was to analyze the properties of a composite that incorporates carbon black and polypyrrole within an Fe3O4/SiO2 core-shell structure, synthesized using the Stöber method under high ultrasonic irradiation conditions (120 W) for Fe3O4/SiO2 nanocomposite. The Fe3O4/SiO2 core-shell indicates magnetochromatic behavior characterized by temperature-dependent coloration and magnetic alignment. Incorporating carbon black and polypyrrole at moderate temperature (5-15 °C) enhanced the electrical conductivity. The electrical resistivity ρ was 7.30 × 106 Ω·cm for Fe3O4, 3.19 × 108 Ω·cm for Fe3O4/SiO2, and 242.56 Ω·cm for Fe3O4/SiO2/PPy-c at room temperature. When it was performed at moderate temperature (5-15 °C), the ρ of the prepared Fe3O4/SiO2 and Fe3O4/SiO2/PPy-c nanocomposite was 1.08 × 108 and 0.00799 Ω·cm, respectively. Current-voltage measurements revealed a linear relationship, with butterfly shaped curves in the forward-bias region for all samples. The Fe3O4/SiO2/PPy-c nanocomposite's tunable synergistic electrical properties at moderate temperatures make it useful for environmental applications, electrical wiring, and circuitry.

Enhancement of structural, optical, electrical, optoelectronic and thermoelectric properties of ZnO thin film via Ni doping and Ni-B co-doping

In this study, the effects of nickel (Ni) and boron (B) elements on the structural, optical, electrical, optoelectronic, and thermoelectric properties of zinc oxide (ZnO) material were investigated. Therefore, undoped ZnO, 3% Ni-doped ZnO (Zn0.97Ni0.03O), and 3% Ni-1% B co-doped ZnO (Zn0.96Ni0.03B0.01O) solutions were prepared by the sol gel method. The produced solutions were coated on glass and p-type Si substrates via dip coating and spraying methods in the form of thin films. We produce pure and n-type semiconductors in the form of nanodots which have wurtzite ZnO polycrystalline structure for all samples. Ni and B co-doped sample is morphologically, electrically and optically enhanced the ZnO material with 3.08 eV band gap, homogenous surface and the highest electrical conductivity. In addition, the best material among the three samples that can be used as a visible light-sensitive sensor is Zn0.96Ni0.03B0.01O under feedback voltage. Technologically, this material can be turned into a photodiode device in the form of Au/Zn0.96Ni0.03B0.01O/p-Si. While the obtained ideality factor of ZnO from the forward bias region decreases from 5.7 to 3.4, its barrier height increases from 0.636 eV to 0.667 eV and serial resistance of contact decreases from 121.6 × 103 Ω to 5.6 × 103 Ω with Ni and B co-doping. Ni doping thin film improves the photovoltaic, and thermoelectric properties of ZnO. Ni-doped ZnO sample can be studied in form of the thin films as a thermoelectric material due to its ZT value is nearly 1.73 × 10–4 at 650 K. Its thermoelectric performance is 13 times better than the that of pure ZnO for the same temperature values. The efficiency of Ni-doped ZnO sample as solar cell increases 10 times compared to pure ZnO. In addition to the production of materials with improved energy efficiency, economical products suitable for use in large areas have been obtained in this study.

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.

Electrical, structural and photovoltaic properties of acceptor dye modified Au/n-Ge heterostructure

n-Ge heterostructure is fabricated using organic dye interlayers such as sulforhodamine-G (SRG) using low-cost spin coating technique and explored its electrical and structural features. The I–V measurements of the Au/SRG/n-Ge heterostructure (HJ) show good rectification behavior. It has been noticed that the barrier height (0.73 eV) of the Au/SRG/n-Ge heterojunction was significantly higher than the Au/n-Ge Schottky diode (SD) (0.63 eV). Cheung's function and the Norde method has been utilized to evaluate the various barrier parameters to understand the non-ideal behavior of the contacts at higher bias region. The low value of the series resistance for HJ (53 Ω) is observed than compared to the SD without organic dye (2974 Ω). Barrier parameters evaluated from the Norde method were compared with those from the Cheung method and found that they confirmed the consistency of Schottky barrier parameters obtained from both techniques. The transport properties of the HJ and SD in the forward bias region are evaluated using the log (I) vs. log (V) plot. At larger forward bias voltages, a change in the drift of current conduction is observed from Ohmic current conduction to traps-assisted SCLC conduction. This may be ascribed to the presence of defects or traps at the n-Ge and SRG interface possibly associated with the organic dye. Also, the photovoltaic properties of the SRG/n-Ge heterostructures were evaluated at 100 mW/cm2 showing significant photoresponse indicates the usage of SRG dyes in photosensitive applications.

Novel PANI:Borophene/Si Schottky device for the sensitive detection of illumination and NaCl salt solutions

Metal/semiconductor structures, particularly Schottky diodes, play a crucial role in semiconductor identification and the production of electronic devices, like solar cells, photodetectors, photodiodes, and field-effect transistors (FETs). These structures are of great interest due to their ability to modify electrical and optical properties, responding to external factors such as illumination and temperature. However, despite extensive research in this field, there has been limited exploration of silicon-based metal/semiconductor structures incorporating PANI:Borophene interfacial materials. In this study, we prepared PANI:Borophene/p-Si and PANI:Borophene/n-Si structures and examined their photodiode properties using various measurements. The unoccupied trap levels (m) obtained 0.44 and 0.33 for Al/PANI:Borophene/p-Si and Au/PANI:Borophene/n-Si device, respectively. Our investigation revealed that both structures exhibited rectification behavior, with linear characteristics in the forward bias region, and deviations attributed to series resistance effects at higher voltages. Moreover, the presence of borophene in the interfacial layer led to improvements in the devices’ electrical properties. Finally, the PANI:Borophene/Si Schottky diodes was tested for salt detection and the Al/PANI:Borophene/p-Si diode has the characteristics of salt (NaCl) concentration detection sensor and it successfully detected salt concentration changes with respect to current flow.

Proximity induced band gap opening in topological-magnetic heterostructure (Ni80Fe20/p-TlBiSe2/p-Si) under ambient condition

The broken time reversal symmetry states may result in the opening of a band gap in TlBiSe2 leading to several interesting phenomena which are potentially relevant for spintronic applications. In this work, the quantum interference and magnetic proximity effects have been studied in Ni80Fe20/p-TlBiSe2/p-Si (Magnetic/TI) heterostructure using physical vapor deposition technique. Raman analysis shows the symmetry breaking with the appearance of A21u mode. The electrical characteristics are investigated under dark and illumination conditions in the absence as well as in the presence of a magnetic field. The outcomes of the examined device reveal excellent photo response in both forward and reverse bias regions. Interestingly, under a magnetic field, the device shows a reduction in electrical conductivity at ambient conditions due to the crossover of weak localization and separation of weak antilocalization, which are experimentally confirmed by magnetoresistance measurement. Further, the photo response has also been assessed by the transient absorption spectroscopy through analysis of charge transfer and carrier relaxation mechanisms. Our results can be beneficial for quantum computation and further study of topological insulator/ferromagnet heterostructure and topological material based spintronic devices due to high spin orbit coupling along with dissipationless conduction channels at the surface states.

Gate leakage mechanisms of the AlGaN/GaN HEMT with fluorinated graphene passivation

The AlGaN/GaN high-electron-mobility transistor (HEMT) passivated by fluorinated graphene (FG) has been investigated. The performances of the HEMTs without passivation before and after F plasma treatment, with FG, Silicon nitride (SiNx), FG/SiNx passivation were contrasted. Compared with the HEMT without F plasma treatment and passivation, the gate leakage current decreases one and a half orders of magnitude after F plasma treatment and SiNx passivated, and four orders of magnitude after FG and FG/SiNx passivated. To study the leakage mechanisms, the temperature dependences of gate leakages have been tested at 323 K–473 K. Through analysis and fitting, the leakages are composed of three components, which are thermionic emission (TE) current, two-dimensional variable range hopping (2D-VRH) current, and Fowler–Nordheim tunneling (FNT) current. TE dominates in the high forward bias region. 2D-VRH dominates in low forward bias. And the chief leakage mechanisms at reverse bias are 2D-VRH and FNT. At 473 K, Schottky barrier height of the HEMT with FG passivation is 1.21 eV. The activation energy and the effective barrier height on the HEMT with FG passivation are 0.64 eV and 0.33 eV respectively. Furthermore, the reasons for the decrement of the gate leakage on the HEMT with FG and FG/SiNx passivation are the enhancement of Schottky barrier heights and augmentation of activation energy. And the improvement in gate leakages for the HEMT passivated by FG/SiNx mainly results from the effect of FG.

Current-voltage (I-V) characteristics of Au/n-Ge heterostructure based on cobalt phthalocyanine (CoPc) interlayer

The influence of cobalt phthalocyanine (CoPc) interlayer on the I-V measurements of Au/n-Ge (pristine) contacts is investigated. I-V characteristics reveals the decrease in the reverse leakage current of CoPc interlayer contacts than compared to contacts without interlayer. The Schottky barrier parameters were described using forward I-V measurements by assuming standard thermionic emission mechanism. The barrier height (BH) of the contact with CoPc interlayer is significantly improved than compared to pristine contact. The observed BHs of pristine and CoPc interlayer contacts are found to be 0.63 eV and 0.67 eV respectively. Reduced interface state density and altered space charges on the n-Ge surface reduces tunneling resistance, may account for the larger BH observed in contacts with CoPc interlayer than pristine contacts. The series resistance evaluated for the contacts using Cheung’s method shows its consistency with Norde method. The observed series resistance value of the Au/CoPc/n-Ge contacts found to be significantly smaller in magnitude than Au/n-Ge contacts. The current conduction mechanism of pristine contact and contact with interlayer was evaluated using double logarithmic I-V plot in the forward bias region. Three regions of conduction mechanisms are observed for Au/CoPc/n-Ge contacts. It is evident that the CoPc interfacial layer considerably changes the conduction mechanism from ohmic conduction to trap charge limited current (TCLC) mechanism at moderately high voltages. The associated transition in the conduction mechanism might be due to the presence of shallow traps (low energy traps) with exponential distribution at the CoPc/n-Ge interface.

High-Speed Photodetector With Simultaneous Electrical Power Generation

We demonstrate a novel 850 nm high-speed photodetector for simultaneous high-speed data acquisition and electrical power generation from the optical signal. The device is based on GaAs/AlGaAs modified uni-traveling carrier photodetector (MUTC-PD). Compared with the traditional p-i-n photodetector with the same absorber thickness, the MUTC device sustains a high 3 dB bandwidth of 11.9 GHz and a power conversion efficiency of 38.5% under a forward bias of +0.7 V. This outstanding performance is achieved by first adopting the MUTC structure on LPC devices. The device is expected to have applications for simultaneous lightwave information and power transfer. Our approach extends the high-speed detection to the forward bias region and may provide a potential solution for next-generation combined power and data transceiver modules.

Effects of fast and thermal neutron irradiation on Ga-polar and N-polar GaN diodes

Studies of the radiation tolerance and electrical behavior of gallium nitride (GaN) based devices are important for the next generation of high-power and high-voltage electronics that may be subjected to harsh environments such as nuclear reactor and fusion facilities, particle accelerators, and post-denotation environments. In this work, we study the behavior of Ga-polar and N-polar GaN Schottky diodes before and after exposure to fast and thermal + fast neutrons. Temperature-dependent current–voltage (I–V) and circular transmission line method (CTLM) measurements were used to study the electrical characteristics. A strong reduction in reverse leakage current and an increase in differential resistance in forward bias were observed after neutron irradiation. Thermionic emission (TE), Frenkel–Poole (FP) emission, and Fowler–Nordheim (FN) tunneling models were used to explain the forward and reverse I–V characteristics pre- and post-irradiation. The study confirms that Ga-polar and N-polar GaN Schottky diodes exhibit different electrical responses to fast and thermal neutron irradiations. The reverse bias characteristics of N-polar diodes are less affected after the fast neutron irradiation compared to Ga-polar diodes, while in the forward bias region, the electrical behavior after fast and thermal neutron irradiations is similar in Ga-polar and N-polar diodes. The results indicate that the role of orientation should be considered in the design of GaN-based radiation-tolerant electronics.

Remarkable Reduction in IG with an Explicit Investigation of the Leakage Conduction Mechanisms in a Dual Surface-Modified Al2O3/SiO2 Stack Layer AlGaN/GaN MOS-HEMT.

We demonstrated the performance of an Al2O3/SiO2 stack layer AlGaN/GaN metal-oxide semiconductor (MOS) high-electron-mobility transistor (HEMT) combined with a dual surface treatment that used tetramethylammonium hydroxide (TMAH) and hydrochloric acid (HCl) with post-gate annealing (PGA) modulation at 400 °C for 10 min. A remarkable reduction in the reverse gate leakage current (IG) up to 1.5×10-12 A/mm (@ VG = -12 V) was observed in the stack layer MOS-HEMT due to the combined treatment. The performance of the dual surface-treated MOS-HEMT was significantly improved, particularly in terms of hysteresis, gate leakage, and subthreshold characteristics, with optimized gate annealing treatment. In addition, an organized gate leakage conduction mechanism in the AlGaN/GaN MOS-HEMT with the Al2O3/SiO2 stack gate dielectric layer was investigated before and after gate annealing treatment and compared with the conventional Schottky gate. The conduction mechanism in the reverse gate bias was Poole-Frankel emission for the Schottky-gate HEMT and the MOS-HEMT before annealing. The dominant conduction mechanism was ohmic/Poole-Frankel at low/medium forward bias. Meanwhile, gate leakage was governed by the hopping conduction mechanism in the MOS-HEMT without gate annealing modulation at a higher forward bias. After post-gate annealing (PGA) treatment, however, the leakage conduction mechanism was dominated by trap-assisted tunneling at the low to medium forward bias region and by Fowler-Nordheim tunneling at the higher forward bias region. Moreover, a decent product of maximum oscillation frequency and gate length (fmax × LG) was found to reach 27.16 GHz∙µm for the stack layer MOS-HEMT with PGA modulation. The dual surface-treated Al2O3/SiO2 stack layer MOS-HEMT with PGA modulation exhibited decent performance with an IDMAX of 720 mA/mm, a peak extrinsic transconductance (GMMAX) of 120 mS/mm, a threshold voltage (VTH) of -4.8 V, a higher ION/IOFF ratio of approximately 1.2×109, a subthreshold swing of 82 mV/dec, and a cutoff frequency(ft)/maximum frequency of (fmax) of 7.5/13.58 GHz.

Variable temperature thermal droop characteristics of 255 nm UV LED

Thermal droop, i.e., the loss of emission efficiency over a certain temperature range, is an important performance bottleneck for the successful commercial application of deep-ultraviolet light emitting diodes. In this study, we examined the mechanism of two thermal droop processes of 255 nm AlGaN quantum well light emitting diodes under temperature stresses in order to obtain steady optical output in a broad temperature range. We discovered that the increase in leakage current in the low forward bias region is accompanied by a decrease in apparent carrier concentration of quantum wells near the p side during the thermal droop process at high temperature (>300 K), indicating that the activation of thermal defects enhances the trap assisted tunneling effect and causes the optical power to decrease more significantly at low current. Compared with normal temperature, the low emission power at low temperatures is attributed to the minority trap H1, which has an activation energy of 0.527 eV at 190 K, according to deep level transient spectrum analysis. At low temperatures above 175 K, the optical power increases as the temperature rises due to enhanced hole injection. By analyzing the droop characteristics, we concluded that the activation of thermal defects is the most probable cause of high temperature thermal droop in 255 nm AlGaN quantum well light emitting diodes, whereas hole trap H1, which is linked to gallium vacancy complexes related defects, is most likely the source of low temperature thermal droop.

A simple method for accurate modeling of diode parameters

Reverse saturation current of diodes is a very small value which cannot be measured with normal measurement devices. In this paper, a simple method to measure the reverse saturation current of diodes is proposed. Then the emission coefficient is calculated with the aid of forward biased region of I-V characteristics. The model extracted with the aid of proposed method shows good agreement with the I-V characteristics of device under test in laboratory experiments.

Design of bevel junction termination extension structure for high-performance vertical GaN Schottky barrier diode

In this work, a vertical GaN Schottky barrier diode with a bevel junction termination extension termination was designed by Silvaco TCAD. The effect of drift layer doping concentration, p-GaN doping concentration and bevel angle are evaluated extensively. With the optimum parameters, the bevel junction termination extension provides conduction path in the forward bias region to reduce the on-resistance and suppresses the electric field crowding in the reverse bias region. Furthermore, the Schottky contact characteristics are not affected in the relatively low bias region. The bevel junction termination extension is promising to achieve low turn-on voltage, low on-resistance and high breakdown voltage.

Effects of boron oxide addition on electrical properties of yttrium-doped bismuth-based zinc oxide varistors

The optimal amount of B2O3 (0.75 mol%) drastically improved the electrical properties of Y-doped varistors, reducing the leakage current to 0.8 μA/cm2 while maintaining exceptionally long-term stability against DC electrical degradation and a varistor voltage around 900 V/mm. Boron ions were found with Bi ions in Y-compounds, which contributed to formation of a Bi-rich glass phase containing B at grain boundaries when the B2O3 content was above 0.75 mol%. The change in microstructure affected the donor density and barrier structure, leading to a change in electrical properties. The Bi-rich phase first reduced the Co concentration in the ZnO grains, thereby decreasing the donor density ND. When large amount of B2O3 was added, some Co remained in ZnO grains, causing an increase in ND. A new analytical method using the differential resistance RD for the nonlinear voltage–current density relation was proposed to clarify the effects of B2O3 addition. This method separates the three differential resistance RDi values (i = 1, 2, 3) and was used to analyze the corresponding conduction process in forward-biased region I, reverse-biased region III, and interface region II of the energy band. The RD1 and RD2 values exhibited junction diode-like behavior in regions I and III. The value of RD2 that correlated with αasMAX and the long-term stability of the varistor and RD3 may be related to region II.

Double-exponential current-voltage (I-V) behavior of bilayer graphene-based Schottky diode

Researches on layered materials such as graphene have attracted lots of attention recently. It has been shown that these materials have make a junction with many semiconductor materials that behave like Schottky diodes and have rectifying characteristics. The comprehension of its fabrication process and properties are a critical need toward graphene-based integrated electronics. The purpose of this study is to find out the current-voltage (I–V) performance of Bilayer Graphene (BLGr) based heterostructure fabricated on Al2O3/p-Si, and the effect of BLGr on diode parameters. Graphene has been grown on copper (Cu) foil by Chemical Vapor Deposition (CVD) method and transferred onto Al2O3/p-Si by using the polymethyl methacrylate (PMMA) wet transfer method. Raman analysis has been performed to obtain supportive information about CVD synthesized graphene film. The I-V plot of the diode exhibited two linear regions named Region 1 (0.08–0.19 V) and Region 2 (0.21–0.40 V). The double-exponential I-V behavior of the diode has been analyzed. The diode characteristics such as barrier height (ΦB0), series resistance (Rs), and ideality factor (n) have been calculated by using thermionic emission (TE), Norde, and Cheung methods. Especially, the values of the barrier height were compared with one another. It was found that they are in good agreement. Additionally, current conduction mechanisms of the diode were investigated using the forward bias ln(I) versus ln (V) plot. At lower and higher forward bias regions, the conduction mechanisms were determined as ohmic behavior and trap charge limiting current mechanism (TCLC), respectively.

Anomalous GIDL Effect With Back Bias in FinFET: Physical Insights and Compact Modeling

In this work, we report a detailed study and modeling of bulk current in the low forward bias region. In the forward bias region, the bulk current shows a gate-induced drain leakage (GIDL) such as strong modulation with gate voltage although from the band alignment one would not expect any tunneling current. We propose physics-based modeling of this effect and derive a compact model for circuit simulators as state-of-the-art compact models are not suitable to capture this effect. The proposed model has been validated with measurement from Intel's bulk FinFET device.

Photodiode working in zero-mode: detecting light power change with DC rejection and AC amplification

We propose a new mode of operation when using a photodiode to extract a variable optical signal from a constant (ambient) background. The basic idea of this 'zero-mode' of operation is to force the photodiode to operate at either zero current or zero voltage. We present possible implementations of this novel approach and provide the corresponding equivalent circuits while also demonstrating experimentally its performance. The gain and bandwidth of the zero-mode photodetector are measured and simulated, and they show highly agreement. The gain compression effect because of the nonlinearity of the forward bias region is also explored. Comparing to the conventional photoconductive photodetector, the zero-mode photodetector is able to obtain higher AC gain and lower noise. With the same component used in the circuit, the measured input referred root mean square noise of zero-mode photodetector is 4.4mV whereas that of the photoconductive mode photodetector is 96.9mV respectively, showing the feasibility of the zero-mode of operation for measuring the small variable light signal under a high power constant background light.

Carrier transport mechanisms of nickel oxide-based carrier selective contact silicon heterojunction solar cells: Role of wet chemical silicon oxide passivation interlayer

We have investigated the carrier transport mechanisms of Ag/ITO/NixO/n-Si/LiFx/Al carrier-selective contact (CSC) silicon solar cells without and with chemically grown SiOx passivation interlayer. The carrier transport is dominated by thermionic (Schottky) emission and tunnelling at the high- (>0.4 V) and low-forward (<0.4 V) bias voltage regions, respectively, in the cell with SiOx interlayer. Without intentionally grown SiOx layer, the carrier transport is dominated by the recombination through interface/surface defect states, which is inferred from the smaller activation energy and strong temperature-dependent ideality factors in >0.4 V forward voltage bias region. The C–V analysis is also confirmed the inability to hold the excess photo-generated charge carriers because of poor interface quality of the cell without SiOx than the cell with SiOx. The NixO/c-Si junction with the SiOx is resulted in higher built-in voltage and better open-circuit voltage representing better interface passivation quality with fewer interface/surface defect states.

Signal and Noise Analysis of an Open-Circuit Voltage Pixel for Uncooled Infrared Image Sensors

An imaging pixel unit-cell topology leveraging a photodetector in the forward-bias region is proposed. Connecting the anode of the photodiode to the gate of a NMOS device operating in the subthreshold region provides the basis for a new open-circuit voltage pixel (VocP) architecture. Theoretical analysis is presented to show the response and performance benefits of the VocP in comparison to a conventional pixel. Based on this analysis, the signal and noise relationships for both pixels are derived and leveraged to construct an end-to-end readout system model. The model results highlight potential performance benefits of the VocP over a conventional direct-injection pixel topology. To verify the analysis, the proposed VocP readout architecture is fabricated along with a conventional direct-injection pixel readout in a $0.18~\mathrm {\mu }\text{m}$ CMOS technology. The VocP performance is compared to a traditional reverse-bias current-mode photodetector configuration. Simulation, modeling, and measurements align with the proposed analytical model. Benefits in system sensitivity and dynamic range are demonstrated showing more than a $2\times $ improvement in noise-equivalent temperature difference and a 4 dB improvement in dynamic range.