Temperature Dependence Of Voltage Research Articles

Comparison of Cell Performance of ZnS(O,OH)/CIGS Solar Cells With UV-Assisted MOCVD-ZnO:B and Sputter-Deposited ZnO:Al Window Layers

ZnO:B films deposited by ultraviolet light-assisted metal organic chemical vapor deposition (UM-ZnO:B) were applied to CBD-ZnS(O,OH)/CIGS solar cells in order to eliminate plasma damages during the subsequent ZnO sputtering. It was verified that the conversion efficiency of CIGS solar cells with a UM-ZnO:B window layer was higher than that of the device with a sputter-deposited(Sp-) ZnO:Al window layer; in both cases, thick (120 nm) and thin (10 nm) ZnS(O,OH) buffer layers were used. The conversion efficiency of CIGS solar cell was improved from 16.3% to 17.5% upon replacement of the Sp-ZnO:Al by a UM-ZnO:B window layer when the thick ZnS(O,OH) (120nm) buffer layer was used. Notably, the conversion efficiency was remarkably improved from 0.2% to 15.6% by the replacement of the window layer even when the ultra thin ZnS(O,OH) (10nm) buffer layer was used. The temperature dependence of open-circuit voltage revealed that interface recombination decreased owing to the use of a UM-ZnO: B window layer.

In Situ Surface Voltage Measurements of Dielectrics Under Electron Beam Irradiation

New instrumentation has been developed for noncontact, in vacuo measurements of the electron beam-induced surface voltage as a function of time and position for nonconductive spacecraft materials in a simulated space environment. The novel compact system uses two movable capacitive sensor electrodes to measure surface charge distributions on samples, using a noncontact method that has little effect on charge dissipation from sample. Design details, calibration, and characterization measurements of the system are presented, with <;1 V to >30 kV surface voltage range, <;0.5 V voltage resolution, and <;1.5-mm spatial resolution. Used in conjunction with the capabilities of an existing ultrahigh vacuum electron emission test chamber, the new instrumentation facilitates measurements of charge accumulation, bulk resistivity, effects of charge depletion and accumulation on yield measurements, electron-induced electrostatic breakdown potentials, radiation-induced conductivity effects, and the radial dispersion of surface voltage. Three types of measurements of surface voltage for polyimide (Kapton HN serve to illustrate the research capabilities of the new system: 1) accumulation using a pulsed electron beam, while periodically measuring the surface voltage; 2) postcharging, as deposited charge dissipated to a grounded substrate; and 3) the evolution of spatial profile resulting from an incident Gaussian beam. Theoretical models for sample charging and discharge are outlined to predict the time, temperature, and electric field dependence of the sample's net surface voltage.

Understanding temperature dependence of threshold voltage in pentacene thin film transistors

Threshold voltage in the pentacene-based organic thin film transistors is found to be linearly increased with decreasing measuring temperature, indicating that the threshold voltage is dominated by the deep hole trapping in an approximately energy-independent trap distribution. The slope of threshold voltage vs temperature is greatly reduced at 200–210 K when temperature is decreased, corresponding to a reduction in the deep trap density. H2O confined in pentacene is considered as one of the sources of the deep hole traps, and the slope change in the temperature dependence of threshold voltage is attributed to the phase transition of supercooled H2O.

On the bandgap of hydrogenated nanocrystalline silicon intrinsic materials used in thin film silicon solar cells

We present optical and electrical measurements of bandgap of hydrogenated nanocrystalline silicon (nc-Si:H). The absorption coefficient (α) does not yield a linear relation on the Tauc plot, indicating that the concept of the Tauc bandgap is no longer valid. The energy at the absorption coefficient α=104cm−1 increases with crystallinity, but it does not imply that the optical bandgap increases with crystallinity. Instead, it reflects the characteristics of mixed-phase material, where the crystalline phase has lower absorption than the amorphous phase. Dark current versus voltage measurements of nc-Si:H solar cells as a function of temperature showed that the products of ideality factor and the activation energy of the pre-factor are the same for nc-Si:H solar cells with different crystallinities. A mobility bandgap at 0K of 1.06eV was derived from these studies. Finally, the temperature dependence of open circuit voltage (Voc) of nc-Si:H solar cells with different Voc values at 25°C shows the same intersection of 1.04eV at 0K. It provides additional evidence that the mobility bandgap is independent of crystallinity and is similar to that of c-Si. The values obtained from both the methods are similar to but smaller than the bandgap of c-Si at 0K; however, the difference could result from experimental errors.

Field Dependent Electrical Conduction in Metal-Insulator-Metal Devices using Alumina-Silicone Nanolaminate Dielectrics

ABSTRACTHybrid alumina-silicone nanolaminate films were synthesized by plasma enhanced chemical vapor deposition (PECVD) process. PECVD allows digital control over nanolaminate construction, and may be performed at low temperature for compatibility with flexible substrates. These materials are being considered as dielectrics for application such as capacitors in thin film transistors and memory devices. In this work, we present the temperature dependent current versus voltage (I-V) measurements of the nanolaminate dielectrics in the range of 200- 310 K to better asses their potential in these applications. Various models are used to know the different conduction mechanisms contributing to the leakage current in these nanolaminate films. It is observed that space charge limited current (SCLC) mechanism is the dominant conduction process in the high field region whereas Ohmic conduction process is contributing to the leakage current in the low field region. The shallow electron trap level energy (Et) of 0.16 eV is responsible for SCLC mechanism whereas for Ohmic conduction process the activation energy (Ea) for electrons is about 0.22 eV. An energy band diagram is given to explain the dominance of various conduction mechanisms in different field regions in these nanolaminate films.

Low-temperature electrical characterization of junctionless transistors

The electrical performance of junctionless transistors (JLTs) with planar structures was investigated under low-temperature and compared to that of the traditional inversion-mode (IM) transistors. The low-field mobility (μ0) of JLT devices was found to be limited by phonon and neutral defects scattering mechanisms for long gate lengths, whereas scattering by charged and neutral defects mostly dominated for short gate lengths, likely due to the defects induced by the source/drain (S/D) implantation added in the process. Moreover, the temperature dependence of flat-band voltage (Vfb), threshold voltage (Vth) and subthreshold swing (S) of JLT devices was also discussed.

Simultaneous Observation of Three Types of Terahertz Radiation from Bi2Sr2CaCu2O8 + δ Intrinsic Josephson Junctions

Terahertz radiation from mesa structures of Bi2Sr2CaCu2O8+δ is detected at various bias points with a Si-bolometer. These radiations are classified into these types: W observed at a current close to the critical current, R and IR observed reversibly and irreversibly, respectively. The type W is the most intense among the three and the radiating condition is complicated. Temperature dependence of radiation voltage of the type R and IR is much more significant than ever seen.

Back-illuminated separate absorption and multiplication AlGaN solar-blind avalanche photodiodes

This letter reports the fabrication and performance of back-illuminated separate absorption and multiplication AlGaN solar-blind avalanche photodiodes. Devices with a 60-μm-diameter active area and a double-mesa structure exhibit a low dark current density of 1.06 × 10−8 A/cm2 at the reverse bias of 20 V and a maximum multiplication gain up to 3000 at the reverse bias of 91 V. The temperature dependence of avalanche voltage shows a large positive temperature coefficient of 0.05 V/K, confirming that avalanche multiplication is the dominant gain mechanism in the photodiodes.

Slow Relaxation Processes in CCTO Detected by Capacitance Versus Voltage Curves

The temperature and frequency dependence of capacitance versus voltage (C–V) curves was investigated for ceramic CaCu3Ti4O12 samples sintered in atmospheres of vacuum, air and oxygen, respectively. A drastic capacitance rise at higher dc voltages and low ac frequencies was observed for all these CaCu3Ti4O12CCTO samples, and it is especially strong for the sample sintered in vacuum, which has not been found previously. The shape as well as the asymmetry of the C–V curves suggest that the dielectric behavior is related to charged trap states. It also indicates that a slow relaxation process, which is strongly correlated with the re‐positioning of oxygen vacancies related trap charges, takes place in CCTO. The main trap charge relaxation process is thought to occur between the boundaries perpendicular and parallel to the external electric field, and the anisotropy of the defect dipoles provide the possibilities for trap charge repositioning which maybe the reason of the huge dielectric constant.

First results on NUV-SiPMs at FBK

In this paper we show selected results on the first release of Near Ultra Violet SiPM technology (NUV-SiPM) produced at FBK. In particular, we focus our attention on the photo-detection efficiency (PDE) performance. The PDE in the near-UV part of the light spectrum is mainly limited by the quantum efficiency term since the photo-generation takes place in a very shallow region of the silicon. Thus, besides using a p+-on-n junction configuration to have an avalanche triggered by the electrons, we need to implement a very shallow p+ layer. In this context, we will show that our NUV-SiPM technology features a quantum efficiency higher than 80% in the measured range between 360 and 420nm. This allows to reach a PDE of about 30% at 9V over-voltage on a SPAD featuring 50×50μm2 cell size and 45% fill factor. We will also show other important features of the device such as noise, breakdown voltage temperature dependence and single-cell response uniformity to prove its functionality.

Active structural vibration control: Robust to temperature variations

d-form augmented piezoelectric constitutive equations which take into account temperature dependence of piezoelectric strain coefficient (d31) and permittivity (∈33), are converted into e-form. Using e-form constitutive equations, a finite element model of a smart two dimensional plate instrumented with piezoelectric patches is derived. Equations of motion are derived using Hamilton's variational principle. Coupled equations of motion are uncoupled using modal analysis. Modal state vectors are estimated using the Kalman observer. The first mode of smart cantilevered plate is actively controlled using negative first modal velocity feedback at various temperatures. Total control effort required to do so is calculated using the electro-mechanical impedance method. The temperature dependence of sensor voltage, control voltage, control effort and Kalman observer equations is shown analytically. Simulation results are presented using MATLAB. Variations in (i) peak sensor voltage, (ii) actual and estimated first modal velocities, (iii) peak control voltage, (iv) total control effort and (v) settling time with respect to temperature are presented. Active vibration control performance is not maintained at temperature away from reference temperature when the temperature dependence of piezoelectric stress coefficient ‘e31’ and permittivity ‘∈33’ is not included in piezoelectric constitutive equations. Active control of vibrations becomes robust to temperature variations when the temperature dependence of ‘e31’ and ‘∈33’ is included in piezoelectric constitutive equations.

Thermal characterization of GaN-based laser diodes by forward-voltage method

An expression of the relation between junction temperature and forward voltage common for both GaN-based laser diodes (LDs) and light emitting diodes is derived. By the expression, the junction temperature of GaN-based LDs emitting at 405 nm was measured at different injection current and compared with the result of micro-Raman spectroscopy, showing that the expression is reasonable. In addition, the activation energy of Mg in AlGaN/GaN superlattice layers is obtained based on the temperature dependence of forward voltage.

Electrical bistable properties of copper phthalocyanine at different deposition rates

Organic bistable memory device is a next-generation of the electrical memory unit. In this paper, we report about the influence of structural properties on electrical bistable behavior of copper phthalocyanine organic memory device. Copper phthalocyanine (CuPc) layer was prepared by thermal evaporation technique at different deposition rates. When the deposition rate is increased, the film crystalline decreases and the surface morphology gradually changes from large flat grain to fine grain structure. Structural parameters such as the crystalline size of CuPc films and dislocation density can be calculated from XRD spectra. Moreover, the effect of deposition rate of CuPC layer on the bistable properties can be performed by current–voltage characteristics, retention measurement, impedance spectroscopy and temperature dependence measurement. The conduction mechanism in both ON and OFF states of the bistable device was analyzed by theoretical model, which can be proposed as a possible trap center of the carrier trapping and de-trapping process by structural defects in CuPc layer. Furthermore, the reliability issue such as cycling endurance and data retention is presented.

Relationship between Work Function of Hole Collection Electrode and Temperature Dependence of Open-Circuit Voltage in Multilayered Organic Solar Cells

We have investigated the photovoltaic properties of multilayered organic photovoltaic devices consisting of indium tin oxide (ITO)/(NiO)/donor/C60/bathocuproine (BCP)/Al structures. Open circuit voltage (VOC) increases with the decrease in temperature between 40 and 350 K. The VOC was, however, pinned at approximately 0.6 V for the device without NiO, probably owing to the insufficient work-function difference between ITO and Al electrodes. The hole injection was also markedly suppressed at the ITO/donor interface in the device with large IP donor materials without the buffer layer and abnormal S-shaped current density–voltage (J–V) characteristics were observed. On the other hand, the value of VOC increases with the increase in ionization potential (IP) of donor materials in the device with NiO buffer layers owing to the enhanced work-function difference of about 1 eV, and the S-shaped curves disappeared at the high temperatures above 200 K. The VOC is further improved to nearly 1.2 V by the UV–ozone treatment of the NiO surface. We have therefore concluded that the increment of work function of the anode caused by the insertion of an oxide buffer layer and the surface treatment of the electrode by UV–ozone treatment are essentially important for the improvement of VOC and charge transport/injection properties in the multilayered organic solar cell applications.

Relationship between Work Function of Hole Collection Electrode and Temperature Dependence of Open-Circuit Voltage in Multilayered Organic Solar Cells

We have investigated the photovoltaic properties of multilayered organic photovoltaic devices consisting of indium tin oxide (ITO)/(NiO)/donor/C60/bathocuproine (BCP)/Al structures. Open circuit voltage (VOC) increases with the decrease in temperature between 40 and 350 K. The VOC was, however, pinned at approximately 0.6 V for the device without NiO, probably owing to the insufficient work-function difference between ITO and Al electrodes. The hole injection was also markedly suppressed at the ITO/donor interface in the device with large IP donor materials without the buffer layer and abnormal S-shaped current density–voltage (J–V) characteristics were observed. On the other hand, the value of VOC increases with the increase in ionization potential (IP) of donor materials in the device with NiO buffer layers owing to the enhanced work-function difference of about 1 eV, and the S-shaped curves disappeared at the high temperatures above 200 K. The VOC is further improved to nearly 1.2 V by the UV–ozone treatment of the NiO surface. We have therefore concluded that the increment of work function of the anode caused by the insertion of an oxide buffer layer and the surface treatment of the electrode by UV–ozone treatment are essentially important for the improvement of VOC and charge transport/injection properties in the multilayered organic solar cell applications.

The Effects of Device Dimension, Substrate Temperature, and Gate Metallization on the Reliability of AlGaN/GaN High Electron Mobility Transistors

ABSTRACTThe effects of source field plates on AlGaN/GaN High Electron Mobility Transistor reliability under off-state stress conditions were investigated using step-stress cycling. The source field plate enhanced the drain breakdown voltage from 55V to 155V and the critical voltage for off-state gate stress from 40V to 65V, relative to devices without the field plate. Transmission electron microscopy was used to examine the degradation of the gate contacts. The presence of cracking that appeared on both source and drain side of the gate edges was attributed to the inverse piezoelectric effect. In addition, a thin oxide layer was observed between the Ni gate contact and the AlGaN layer, and both Ni and oxygen had diffused into the AlGaN layer. The critical degradation voltage of AlGaN/GaN High Electron Mobility Transistors during off-state electrical stress was determined as a function of Ni/Au gate dimensions (0.1-0.17μm). Devices with different gate length and gate-drain distances were found to exhibit the onset of degradation at different source-drain biases but similar electric field strengths, showing that the degradation mechanism is primarily field-driven. The temperature dependence of sub-threshold drain current versus gate voltage at a constant drain bias voltage were used to determine the trap densities in AlGaN/GaN high electron mobility transistors (HEMTs) before and after the off-state stress. Two different trap densities were obtained for the measurements conducted at 300-493K and 493-573K, respectively.

Temperature Dependences of Jump Voltage in Bi2Sr2CaCu2Ox Intrinsic Josephson Junctions

Abstract The basic experimental features of voltage jump V J, between two adjacent branches in stacked Bi2Sr2CaCu2Ox intrinsic Josephson junctions (IJJs) are discussed. The temperature dependence of the V J normalized to its value at 4.2 K, V J( T )/ V J(4.2K), exhibited a downward deviation from a BCS temperature dependence of gap voltage. In this study, we assume that the critical current I c, much smaller than that expected from the Ambegaokar-Baratoff (AB) theory is the intrinsic feature for IJJs. To interpret the V J( T ) characteristics, the linear approximation for the subgap quasiparticle current is also examined and a linear subgap resistance model is proposed as follows: R J,sg( T )= R J,sg(0)/[1+exp( k o( T - T c/2)], where k o is constant. Under these assumptions, the voltage jump is given by V J( T )= R J,sg( T ) x I c( T ). The normalized V J( T )/ V J(4.2) characteristics for all samples with different V J and I c values are well explained using this model.

Investigating the effect of off-state stress on trap densities in AlGaN/GaN high electron mobility transistors

The temperature dependence of sub-threshold drain current versus gate voltage at a constant drain bias voltage were used to determine the trap densities in AlGaN/GaN high electron mobility transistors (HEMTs) before and after the off-state stress. Two different trap densities were obtained for the measurements conducted at 300–493 K and 493–573 K, respectively. The trap density at the lower temperature range almost doubled from 1.64 × 1012 to 3.3 × 1012/cm2–eV after a critical voltage for degradation of HEMTs was reached during the off-state drain voltage step-stress. The trap density at the higher temperature range only slightly increased from 8.1 × 1012 and 9.2× 1012/cm2–eV after the device stress. The trap densities were also strongly dependent on drain bias voltage; measurements conducted at higher drain bias voltages exhibited larger trap density due to more hot electrons generated at these conditions.

Temperature dependence of InGaN/GaN multiple quantum well based high efficiency solar cell

In this paper, a new p–InGaN multiple quantum well–n solar cell has been investigated. In order to obtain the exact solar cell parameters such as conversion efficiency, the polarization field effects of nitride materials are taken into account. It has been found that the conversion efficiency of the p–i(MQW)–n solar cell is significantly higher than those of normal p–i(bulk)–n solar cells. The optimized conversion efficiency of about 35% is obtained for p–MQW–n solar cells at room temperature. Also, the temperature dependence of open-circuit voltage and short-circuit current and consequently conversion efficiencies of both structures are investigated, and it is observed that the increasing of temperature slightly increases the short-circuit current and decreases the open-circuit voltage and efficiency.

Experimental and TCAD Study of Breakdown Voltage Temperature Behavior in $n^{+}/p$ SiPMs

In this paper, the breakdown voltage in avalanche photodiodes operating in Geiger mode is investigated. In particular, the breakdown voltage dependence on the structural characteristics of n+/p avalanche diodes, such as implant dose and epitaxial layer thickness and doping concentration, as well as the temperature behavior are analyzed. The study includes both experimental data and numerical simulations. The first are acquired in a controlled temperature environment on samples featuring different electrical structures. Simulations are performed both at the technological process as well as at the electrical level using a commercial TCAD software. Agreement between experiments and numerical analysis is found to be quite good and first hints on how to improve the breakdown voltage uniformity and temperature dependence are given. Moreover, with the aid of TCAD simulations, the potential sources of device breakdown voltage fluctuations related to both device process variability and the properties of the starting silicon wafers are investigated.