Reverse Current Increases Research Articles

Strategically constructed AlGaN doping barriers for efficient deep ultraviolet light-emitting diodes.

Here, we propose a sandwich-like Si-doping scheme (undoped/Si-doped/undoped) in Al0.6Ga0.4N quantum barriers (QBs) to simultaneously promote the optoelectronic performances and reliability of deep ultraviolet light-emitting diodes (DUV-LEDs). Through experimental and numerical analyses, in the case of DUV-LEDs with conventional uniform Si-doping QB structure, severe operation-induced reliability degradation, including the increase of reverse leakage current (IR) and reduction of light output power (LOP), will offset the enhancement of optoelectronic performances as the Si-doping levels increase to an extent, which hinders further development of DUV-LEDs. According to a transmission electron microscope characterization and a numerical simulation, an improved interfacial quality in multiple quantum wells (MQWs) and more uniform carrier distribution within MQWs are demonstrated for our proposed Si-doping structure in comparison to the uniform Si-doping structure. Consequently, the proposed DUV-LED shows superior wall-plug efficiency (4%), IR at -6 V reduced by almost one order of magnitude, and slower LOP degradation after 168-h 100 mA-current-stress operation. This feasible doping scheme provides a promising strategy for the high-efficiency and cost-competitive DUV-LEDs.

Simulation study for anode engineering of AlGaN/GaN double-channel hybrid anode Schottky barrier diode

In this work, a new structure of double-channel hybrid anode Schottky barrier diode with dual anode metal (DCH-DM-HAD) was proposed, and the preliminary investigation of the device's electrical characteristic was conducted by using Silvaco TCAD tools. The double-channel hybrid anode diode (DCH-HAD) and single channel hybrid anode diode (SCH-HAD) were compared and it was found that the Ron at lower forward bias is twice as large as the higher bias, which is attributed to different Von of upper channel and lower channel. It can be avoided by setting different metal structures at anode. Besides, the Von decreases with increasing thickness of the barrier layer, but the reverse leakage current increases fast. Finally, the breakdown voltage of three different structures of hybrid anode diodes were compared, and it is found that replacing nickel with tungsten is harder to form uniform electric field due to difference of workfunction of tungsten and nickel. Nonetheless, these kinds of diodes own excellent electrical characteristics.

Морфология и электрофизические свойства модифицированных ленгмюровских пленок оксида графена

The work devoted to study of the electrical properties and morphology of Langmuir-Blodgett films of modified graphene oxide (GO). The Langmuir-Blodgett method was used for studying of formation process of Langmuir monolayers formed on the subphase contained dissolved ions of tin chloride salt. The compression isotherms of monolayers formed in the presence of tin ions shifted towards larger occupied areas. Langmuir monolayers of graphene oxide formed under various conditions were transferred on solid substrates and studied by atomic force microscopy and voltammetry. It has been established that the presence of tin ions in the aqueous subphase leads to changes in the morphology of the formed films. Thus, the average roughness and surface area of such films increased from 0.2 nm and 0.04 μm2 to 5.4 nm and 0.46 μm2, respectively. The presence of tin ions dissolved in the aqueous subphase influenced the type of current-voltage characteristics of the films under study. The maximum reverse current increases from 075 nA to -0.3 nA and the resistance increases from 11 GOhm to 700 GOhm. Temperature annealing of the graphene oxide film at 300°C leads to a decrease in the maximum forward current and an increase in the reverse current from 0.0407 nA and -0.071 nA to 0.0065 nA and 0.0616 nA, respectively. For a film formed in the presence of ions in the subphase, annealing does not affect the maximum forward current, and the current of the reverse branch of the current-voltage characteristic increases from -0.1669 nA to 0.0468 nA.

Electrophysical parameters of p-i-n photodiodes, irradiated with 60Co γ-quanta

The results of studies of changes in the electrical parameters of p-i-n photodiodes manufactured on monocrystalline silicon wafers of p-type conductivity orientation (100) with ρ = 1000 Ohm cm, when irradiated with γ-quanta from a 60Co source, are presented. It has been established that as a result of irradiation of p-i-n photodiodes with doses up to 2·1015 quanta/cm2, the reverse dark current increases by more than an order of magnitude. However, the shape of the curve of the dependence of the current on the applied reverse voltage of irradiated p-i-n photodiodes does not change qualitatively, as for the original devices there are three regions with different dependences of current on voltage: sublinear, superlinear and linear, due to different mechanisms of generation-recombination processes in the depletion region of the p-n junction. The main reason for the increase in the reverse current of p-i-n photodiodes as a result of irradiation with γ-quanta is the formation of generation-recombination centers of radiation origin due to the condensation of primary radiation defects (vacancies and/or self-interstitial atoms) on technological residual structural defects formed during the growth of silicon single crystals, and during subsequent high-temperature treatments during the formation of devices.

Study on electronic transport performance of Ag-ZnO film by photoassisted conductive atomic force microscopy

Purpose The purpose of this paper is to study the electronic transport performance of Ag-ZnO film under dark and UV light conditions. Design/methodology/approach Ag-doped ZnO thin films were prepared on fluorine thin oxide (FTO) substrates by sol-gel method. The crystal structure of ZnO and Ag-ZnO powders was tested by X-ray diffraction with Cu Kα radiation. The absorption spectra of ZnO and Ag-ZnO films were recorded by a UV–visible spectrophotometer. The micro electrical transport performance of Ag-ZnO thin films in dark and light state was investigated by photoassisted conductive atomic force microscope (PC-AFM). Findings The results show that the dark reverse current of Ag-ZnO films does not increase, but the reverse current increases significantly under illumination, indicating that the response of Ag-ZnO films to light is greatly improved, owing to the formation of Ohmic contact. Originality/value To the best of the author’s knowledge, the micro electrical transport performance of Ag-ZnO thin films in dark and light state was firstly investigated by PC-AFM.

Effects of electric polarization and defect energy levels induced by ion irradiation on the electrical behavior of 4H-SiC Schottky barrier diodes

The effects of electric polarization and defect energy levels induced by C4+ irradiation on the electrical behavior of 4H-SiC Schottky barrier diodes (SBDs) are discussed. The parameters of the SBDs were extracted from capacitance–voltage (C–V) and current–voltage (I–V) measurements, the deep level transient spectroscopy (DLTS) was used to identify defect energy levels. In addition, the dielectric function and energy band structure of 4H-SiC were calculated using a first-principles approach to verify the enhancement of polarization and the origin of the defect energy levels. The results show that the net (donor) carrier concentration (N d) increases with the increase of irradiation fluence, which is caused by the competition between irradiation-induced defects and the polarization effect. On the one hand, Z 1/2 is determined by DLTS. It is related to the doubly negatively (2-|0) charged state of V c (carbon vacancy), which is a double acceptor. The intensity of the Z 1/2 peak increases with increasing irradiation fluence, which means that the defects caused by irradiation should reduce the N d. On the other hand, the polarization effect does exist and it becomes stronger with the increase in the irradiation fluence, which makes the N d increase. Obviously, the polarization effect induced by the irradiation is dominant for N d when the depth of ion penetration is in the shallow layer behind the metal–semiconductor (M–S) interface. Irradiation induced electron traps and an uneven distribution of positively charged centers, which can cause ln(I)-V to exhibit a non-linear component before reaching the turn-on voltage. The series resistance (R s), reverse current (I R) increase and the forward current decreases with the increase in irradiation fluence. All these show that the irradiation causes degradation of Ni/4H-SiC SBD performance.

Accelerated aging of unencapsulated flexible GaInP/GaAs/InGaAs solar cells by means of damp heat and thermal cycling tests

The extended damp heat and thermal cycling tests were performed on unencapsulated flexible thin-film GaInP/GaAs/InGaAs solar cells to assess the long-term stability. The solar cells were subjected to 85 °C/85% damp heat test for more than 1000 h and 420 cycles of thermal cycling test between −60 °C and 75 °C, respectively. The performance attenuations of flexible solar cells were less than 2% in both cases, which were due to the slow decline of the open-circuit voltage with aging time. The slight decrease in open voltage was attributed to the increase in reverse saturation current due to the enhanced recombination, which was in good agreement with the calculation based on the two-diode model. The good performance of the unencapsulated flexible GaInP/GaAs/InGaAs solar cells in severe environment indicated the stable and reliable device fabrication art in the experiment.

Heavy Ion Induced Degradation Investigation on 4H-SiC JBS Diode with Different P+ Intervals

The heavy ion radiation response and degradation of SiC junction barrier Schottky (JBS) diodes with different P+ implantation intervals (S) are studied in detail. The experimental results show that the larger the S, the faster the reverse leakage current increases, and the more serious the degradation after the experiment. TCAD simulation shows that the electric field of sensitive points directly affects the degradation rate of devices with different structures. The large transient energy introduced by the heavy ion impact can induce a local temperature increase in the device resulting in lattice damage and the introduction of defects. The reverse leakage current of the degraded device is the same at low voltage as before the experiment, and is gradually dominated by space-charge-limited-conduction (SCLC) as the voltage rises, finally showing ballistic transport characteristics at high voltage.

Influence of heavy ion irradiation and high temperature on the performance of 4H–SiC Schottky barrier α particle detector

Traditional semiconductor detectors such as silicon and germanium are easily affected by ambient temperature and charge-particle ion's radiation. They can't work stably in harsh environments such as high temperature and strong radiation for a long time. In this paper, 4H-silicon carbide detectors based on a Schottky barrier diode (SBD) were fabricated and the combined influences of high temperatures and heavy ion irradiation on 4H–SiC detectors have been investigated. With no radiation, the 4H–SiC detectors have excellent I–V characteristics performance during a temperature range of 30–200 °C. Even at an ambient temperature of 200 °C, the leakage current of the 4H–SiC detector was only 107 nA at the full depletion voltage. Then 280 KeV C4+ heavy ions were used to irradiate the 4H-silicon carbide detectors, and the performances of the irradiated detectors were studied for different radiation doses from 1 × 1013 to 1 × 1016 ions/cm2 in a certain higher ambient temperature environment. For the fully depleted 4H-silicon carbide detectors in an ambient temperature of 140 °C, both the I–V characteristics and the energy resolution have shown a certain radiation damage at the radiation fluence of 1 × 1015 ions/cm2, while a significant deterioration was observed when the radiation fluence is up to 1 × 1016 ions/cm2. It means that the 4H–SiC detectors can withstand an irradiation dose of 1 × 1015 ions/cm2 at 140 °C. The time-dependent I–V curves were also investigated for the irradiated detectors for a standing time up to 192 h, and it's found that the irradiated detectors had minor changes in the leakage currents during a long time standing. A PN junction model with current and voltage equations was used to explain the phenomenon that the reverse leakage current increases with the increase of temperature. The surface recombination model was also used to explain the deterioration of I–V characteristics and energy resolution after irradiation.

Effect of Schottky annealing temperature on reverse leakage current of 6500 V 4H-SiC JBS diodes

Annealing treatment has an important effect on the electrical properties of Schottky diodes. In this paper, the effect of Schottky annealing temperature on reverse leakage current of 6500 V 4H-SiC JBS diodes was studied. The reverse leakage current of the diode annealed at 500 °C is higher than that of the diode annealed at 450 °C. This is because the Schottky barrier height of the diode annealed at 500 °C is decreased by 0.08 eV, which leads to a large reverse leakage current. Meanwhile, the Schottky barrier height of the diode annealed at 500 °C is decreased more significantly with the increase of measurement temperature, therefore the reverse leakage current increases significantly.

GaAs radiation-degraded detectors: gamma spectrometry at lowered temperatures

The GaAs detectors are radiation hard against a few MGy of high-energy (MeV) electrons. The main reason for detector functionality degradation is the reduction of their charge collection efficiency and together with reverse current increase these facts cause the drop of the signal to noise ratio down to close to 1, disabling detector functionality. In this paper, the lowering of detector temperature has improved the spectra of less ionizing particles, the 59.5 keV gamma rays, measured by semi-insulating GaAs pad detectors, which were first degraded by 8 MeV electrons with a dose of 200 kGy. The signal to noise ratio improved by about 30%, from 1.09 at room temperature up to 1.42 at 276 K. The photo-peak was easily distinguishable from the noise during cooling and the calculated detector relative energy resolution improved from 46% at room temperature to 34% at 276 K. A mild decrease in detector charge collection efficiency was observed, by about 5% of its initial value, when cooling the detector to 276 K.

The effect of dissolution by periodic reverse current on the microstructure of bamboo-shaped porous anodic alumina

• Periodic reverse current with small amplitude can promote the growth of the porous layer. • Periodic reverse current has the effect of pore expansion. • The water reduction speed increases during the reverse voltage stage. • The ions driven by the electric field change with the direction of current. • H+ (H2O) and OH− are the main ions that move in the reverse voltage stage. In this paper, the effects of a cyclic anodizing method with the introduction of periodic reverse current are reported. The effects of the periodic reverse current on the microstructure of bamboo-shaped porous anodic alumina (PAA) film are investigated using positive and negative current triangular waveforms. The results of the experiment showed that when the reverse current in each current cycle was I D ' = -5 mA, the growth velocity was the fastest. The analysis found that the introduction of the periodic reverse current was beneficial to increasing the growth velocity of the porous anodic alumina film and had the additional effect of pore expansion. However, with any further increase of the periodic reverse current, the growth velocity of the porous anodic alumina film gradually decreased, and the period length showed a decreasing trend. The main reason for this phenomenon is that in a larger reverse voltage phase, the ions driven by the electric field are mainly H + (H 2 O) and OH − . Then the reaction that occurs is mainly dissolution. With large pore size and adjustable period length, this porous anodic alumina film can be used as a template for the synthesis of nanomaterials, which have practical significance for the synthesis of nanodevices.

A SiC sidewall enhanced trench JBS diode with improved forward performance

A new high-performance sidewall enhanced trench junction barrier Schottky (SET-JBS) diode is proposed in this article. In the proposed SET-JBS diode, in addition to the Schottky contact on the top anode, the sidewall of the trenches also introduces Schottky contacts, which not only increases the Schottky contact area, but also weakens the junction field-effect transistor effect of the device, resulting in a high forward current density and a low specific on-resistance (R on,sp) with a small increase in reverse leakage current (J L). Simulation results show that the R on,sp of the proposed SET-JBS diode is reduced by 21.6%–46.7% with less than an order of magnitude increase in leakage current compared with that of the conventional trench JBS (T-JBS) diode when the trench distance is from 2.1 μm to 1.2 μm at the 2 μm trench depth. And the SET-JBS diode also performs better than the trench MOS barrier Schottky (TMBS) diode when comprehensively considered the R on,sp and J L. And the figure of merit and the trade-off relationship between the R on,sp and the breakdown voltage of the proposed SET-JBS both are better than those of the conventional T-JBS diode and TMBS diode. The forward I–V analytical model of the SET-JBS is also proposed, which is in good agreement with the simulation results. All the simulation results indicate that the proposed SET-JBS diode has promising potential in power electronics applications.

Influence of α-particles irradiation on the properties and performance of silicon semiconductor detectors

Deterioration of the operation parameters of p-type Si surface-barrier detector and Si(Li) p-i-n detector upon irradiation by alpha-particles was investigated. The detectors were irradiated at room temperature up to a total number of the registered α-particles Nα equal to 6 × 109. Prolonged irradiation has resulted in a deterioration of the detectors energy resolution ability and it was found that the increase of α-peaks broadening can be described by a linear function of Nα with a slope Δσ/ΔNα ∼ (1.4–1.8) × 10–9 keV/α for both detectors. Resolution deterioration was associated with the increase of the detectors leakage current, which proceeds linearly with the number of absorbed α-particles with the slope ΔI/ΔNα ∼ (7-17) × 10-17 A/α. The increase of the detectors reverse current was related with appearance of radiation-induced defect level at 0.56 eV above the valence band.

Effect of Hydrostatic Pressure on the Revers Gate-Current of AlGaN/GaN HEMTs

In this paper, we present an Analytical-Numerical model for reverse gate leakage current in AlGaN/GaN high electron mobility transistors (HEMTs), which investigate the influence of the hydrostatic pressure (HP) on gate-current. Salient features of the model are incorporated of occupied sub-bands in the interface quantum well, combined with a self-consistent solution of the Schrödinger and Poisson equations. Finite difference techniques have been used to acquire energy eigenvalues and their corresponding eigenfunctions of AlGaN/GaN (HEMTs). It has been found that the bound charge at the heterointerface has the most impact on the threshold voltage. The increases in hydrostatic pressure cause an increase in threshold voltage. With increasing HP, the Schottky barrier height decreases, AlGaN electric field and reverse gate leakage current are increased. The increase in HP acts as a positive virtual gate. The dependence on the HP of Poole- Frenkel emission (FP) and Fowler-Nordheim (FN) direct tunneling is more than trap-assisted-tunneling (TAT). Increasing the pressure of 2GPa, the intersection point of PF and TAT varies by 1 volt, the reverse gate current increases by an average of 35%, and the threshold voltage increases to 1.15 V in absolute terms.

Structural and optical properties of pure ZnO and Al/Cu co-doped ZnO semiconductor thin films and electrical characterization of photodiodes

Abstract Nano-structured semiconductor thin films and p-type Si photodiodes were fabricated with the sol-gel spin coating technique using pure ZnO and co-doped ZnO:Alx:Cuy with x = 1 at.-%, y = 1, 2, 3, 5 at.-%. The structural and optical properties of thin films were examined using an XRD and a UV-spectrophotometer. The thin films have a hexagonal wurtzite crystal structure, and their optical band gap energies decrease with increasing Cu contribution. The electrical properties of photodiodes were assessed via I-V, C-V, (G/ω)-V and phototransient current (I-t, C-t) measurements. The Φ b(I-V), experimental zero-bias barrier height, rectification ratio, ideality factor and Ion/Ioff parameters of the diodes were calculated using thermoionic emission model. In addition, Φ b(C-V), barrier height, Vbi, built-in voltage, Vd, diffusion potential, Nd, donor concentration and Wd, depletion layer width of p-Si/ZnO:Alx:Cuy (x = 1 at.-%, y = 1 at.-%.) photodiodes were obtained using a C-2-V graph plotted at 1 MHz frequency. The photodiodes exhibit rectifying and photosensitive behaviors, and their reverse bias current increases with increasing light intensity. These results indicate that produced diodes can be employed as photodiodes or photosensors in optoelectronic circuits and electronic devices.

Investigation of 4H-SiC Schottky barrier diodes irradiated with 6 MeV Au ions at low temperature

The change in the electrical properties of 4H-SiC Schottky barrier diodes (SBDs) irradiated by 6 MeV Au ions at low temperature (LT) is investigated. The SBDs are characterized by current–voltage (I-V) and capacitance–voltage (C-V). The SRIM software is used to calculate the Au ion transportation process. The experimental results indicate that the ideality factor (n) and the reverse leakage current (IR) increase, and Schottky barrier height (SBH) decreases with the increase in fluence. It is found that series resistance (RS) and effective impurity concentration (ND) are recovered at 5 × 1015 ions/cm2. Calculation results show that the mental layer can prevent most of the Au ions, while the secondary particles will enter the SiC layer. Therefore, these results demonstrate that the secondary particles induce many defects at the metal-SiC interface and the SiC epitaxial layer after LT heavy ion (HI) irradiation.

ELECTRICAL AND PHOTOELECTRIC PROPERTIES OF SCHOTTKY DIODES GRAPHITE/n-Si PREPARED BY THE PENCIL-ON-SEMICONDUCTOR METHOD

This paper reports the results of an investigation of electrical properties photosensitive Schottky diodes graphite/n-Si prepared for the first time by the transfer of dry drawn graphite films onto single crystal n-Si. Barrier parameters were determined and C-V characteristics was studied. The dominating mechanisms of current transfer through the heterojunction have been determined: at forward bias is well described within of tunneling-recombination models via surface states at the graphite/n-Si interface, at reverse bias was determined to be the small current flows through the shunt resistance. It was found that under illumination with white light with an intensity Popt = 80 mW/cm2, the reverse current Ilight increases by more than an order of magnitude in comparison with its value in the dark Idark due to the separation of photogenerated electron-hole pairs. From the above, it can be conclude that the fabricated Schottky diodes can be use as a photosensitive device.

The Research of Piezo Phototron Effect in A2B6 Film Structures

The paper presents the results of the study of a piezo phototron effect in hetero structures based on A2B6 films. The field of study of the piezo phototron effect in semiconductor thin films is new. The use of materials that have several properties at the same time, namely semiconductors, piezoelectrics and photoelectric properties, allows us to create a fundamentally new class of semiconductor devices, especially in the field of sensors and photovoltaics. Obtaining films of the A2B6 group, which include CdS, CdTe, CdSe, ZnS, ZnSe, ZnO with an existing piezoelectric effect, is an urgent task. In this work, the object of study is diode structures based on them. Namely, CdS films were grown by thermal evaporation on a flexible molybdenum substrate. A thin layer of degenerate CuxS semiconductor was deposited on top of the CdS films, which allowed it to form a diode barrier structure. For the study of photodiode properties, measurements were made of the current-voltage characteristics (VAC) in the dark and light modes. Measurements were made using a power source, a voltmeter and an ammeter. The limits of voltage measurements ranged from -2 V to 2 V to prevent possible breakdown of structures. A white LED with a power output of 30mW / cm2 was used as the light source. From the obtained CVCs it was obtained that a rectifying barrier is formed between the semiconductor films and the structure has a diode characteristic. The magnitude of the reverse current increases during illumination. Pressure was applied to the diode structures to investigate the piezoelectric effect. The pressure applied to the sample was changed by means of levers weighing 10, 20, 50, 100 and 200 grams. As a result of the measurements of the CVC during the application of pressure, it was found that the current on the forward and reverse branches of the CVC showed an increase in both the dark mode of measurement and in the light. This indicates the presence of a piezoelectric effect in this heterojunction. The calculated values of the sensitivity to pressure showed that the current on the back and forward branches of the CVC changes at different intervals. The highest sensitivity in the range 0–77.31 absolute units is observed for reverse current without illumination. With additional illumination, the sensitivity to the pressure on the back branch of the CVC decreases and is 0–7.73. All measurements made show the presence of a piezophototron effect, which allows the creation of new functional devices for measuring pressure and luminance based on this heterojunction.

Comparative study of In/CdTe/Au Schottky- and p–n junction-diode detectors formed by backside laser irradiation doping

Two types of In/CdTe/Au diode structures were fabricated using detector-grade p-CdTe single crystals: (i) by vacuum evaporation of In and Au contacts on the chemically treated (111) surfaces; (ii) by backside laser doping when the In/CdTe structures were irradiated from the crystal side with a wavelength for which the semiconductor was transparent. Thus, diodes with a Schottky contact (In/CdTe) and a p–n junction were obtained, respectively. To prove the doping of the thin region near the In/CdTe interface by In (donor) and study thermal tolerance of both types of In/CdTe/Au diode detectors, room temperature I–V characteristics and 57Co isotope emission spectra were measured before and after annealing of the diodes at temperatures below and above the In melting point. Thermal annealing at lower temperatures led to a slight increase and decrease in reverse dark current of the unirradiated and laser-irradiated samples, respectively. Heating up to 200 °C resulted in a significant increase in reverse current and complete spectra degradation in the samples fabricated without laser processing. After such annealing, the electrical characteristics of the p–n junction diodes, formed by the backside laser doping technique, became optimized and 57Co spectra were almost unchanged. It was supposed that a Schottky barrier at the In/CdTe interface was degraded, while a p–n junction, created in a deeper region of the CdTe crystal, remained functional even after melting and solidifying the In contact.