Open Circuit Voltage Decay Method Research Articles

New equations to calculate carrier recombination lifetime of silicon epitaxial layer, based on open circuit voltage decay method

Abstract New equations for recombination lifetime calculation based on the open circuit voltage decay (OCVD) method were proposed. The new equations can yield accurate recombination lifetime values of the i-layer of PiN diodes in which a silicon epitaxial layer is employed, by eliminating the effects of carrier diffusion into p+ and n+ layers from the i-layer of PiN diodes, carrier injection into the i-layers from the depletion layer of PiN diodes, and surface recombination on the side wall of PiN diodes. To verify the effectiveness of the new equations, OCVD measurements were performed by employing technology computer-aided design (TCAD) simulation and actual PiN diodes. Although the calculated values implied the effect of epitaxial layer thickness, they were consistent with the results obtained under assumed lifetime conditions for TCAD simulation, the theory of recombination lifetime, and results in other reports.

English

In this manuscript, we present a study on the effects of magnetic field on charge carrier effective lifetime within the base of a polycrystalline PV solar cell p-n junction. This study is elaborated in two forms as a theoretical study and an experimental study. Indeed, under various magnetic field values, PV solar cell is illuminated by using the light from stroboscopic. From a theoretical approach mainly use the open circuit voltage decay method.  Green’s functions and boundaries conditions are used to solve charge carrier’s diffusion equation. Open circuit transient voltage decay expression is found. The charge carriers’ effective lifetime values inversely proportional to the slope of open circuit voltage decay curve are deducted. A simple experimental set-up used open circuit voltage decay method mainly, these experimental measurements of charge carriers’ effective lifetime are done and the effects of magnetic field are then outlined. Globally, magnetic effects on effective charge carrier lifetime are then analyzed. These two types of results obtained present qualitatively the decay of charge carriers’ effective lifetime when magnetic field increase. In the first time, theoretical results and experimental results are in good agreement and in the second time these results are in good agreement with literature results. Key words: Effective lifetime, open circuit voltage decay, magnetic field.

OCVD Measurement of Ambipolar and Minority Carrier Lifetime in 4H-SiC Devices: Relevance of the Measurement Setup

The open-circuit voltage decay (OCVD) method is a well-known technique for conducting electrical measurements of carrier lifetime: the main advantages lie in the simple setup and the possibility of carrying out measurements in commercial devices without the need of removing the package, as for optical methods. Despite several researchers having reported carrier lifetimes measured by the OCVD method in different devices, there has been little discussion about the potential effect of the experimental setup on the obtained results. By comparing the outputs of the experimental measurements with those of numerical simulations, this study investigates the overlooked effect of the OCVD measurement setup on the former. Due to the growing importance of SiC-based devices, the analysis is applied to a 4H-SiC p-i-n diode. Two main points are addressed: 1) the effect of circuit setup on the ambipolar lifetime is discussed and a method, originally developed for improving the estimate of low-level carrier lifetime in OCVD measurements, is used to correct the measured lifetime for this influence; 2) the origin of the local minimum eventually appearing in the lifetime versus time curves is also investigated. It is found that the minimum can also be related to the time constant of the experimental setup, giving rise to doubts about the usual interpretation of this minimum as the minority carrier lifetime. A method is thus proposed to help discriminate between the two interpretations.

(Invited) Sn Based Perovskite Solar Cells on Glass Substrate and Plastic Substrate

Lead-based perovskite solar cells (PSCs) with small cell area have achieved a conversion efficiencies of higher than 25 %. Because of the Pb ion concern, various Pb-free PSCs also have been explored such as Bi, Ge, Ag, and Sn-PSCs. Among then, Sn-PSCs are is the most promising candidate. In this presentation, to begin with, the effect of the photo-voltaic performance caused by Ge ion doping, A site cation replacement, and surface passivation are reviewed briefly from the view point of the carrier concentration, carrier life time, crystal lattice strain, and band alignment. Recently, We reported the correlation between lattice strain relaxation and the power conversion efficiency of Sn-PSCs by substituting the A site with cations of various ionic radii(1). From the study, we knew the unique behaviors of ethylammonium iodide (EAI) replacement at A site cation, giving the efficiency over 13 %. After the brief review, especially, the effect of EAI addition on the enhanced efficiency is discussed. There is some works previously on EAI replacement at A site(2).The formulation with Ge ion doped Sn-perovskite with an inverted structure is used as the discussion. The lattice disorder induced by the A site cation size has detrimental effects on the charge carrier dynamics in perovskite semiconductors. Among them, EAI promoted crystal growth towards preferred crystal orientation and caused the crystal lattice expansion, suggesting that bigger EA+ cation is incorporated in the perovskite crystal structure. The addition of EAI decreased the lattice strain, shifted the band edge absorption towards lower wavelength, and caused blueshift of the PL, showing that the introduction of EAI makes band gap a little wider. PL lifetime became longer from 12.9 ns to 20.1 ns after the addition of EAI. Efficiency of solar cells consisting of FTO/PEDOT:PSS/Sn-PVK/C60/BCP/Ag/Au was enhanced from 9.20 % ( JSC of 23.38 mA cm-2, VOC of 0.56 V and FF of 0.70) to 9.86 % ( JSC of 23.41 mA cm-2, VOC of 0.59 V and FF of 0.71) after EAI addition. After optimization, the efficiency reached a high value of 10.80 % with a JSC of 23.05 mA cm-2, a VOC of 0.62 V and a FF of 0.75. The increased in the device performance with EAI addition was attributed to the significant increase in the VOC. We have already published a report regarding this phenomenon in which we attribute this to the lattice strain relaxation of the perovskite crystal(1). The ideality factor is decreased from 1.47 to 1.26. By using open-circuit voltage decay (OCVD) method, we proved that the addition of EAI minimizes the charge carrier recombination process and as a result showed longer carrier lifetime. Further optimization of the best device is performed by surface passivation using Lewis base following our previous report(3). This helped to increase the efficiency even further to an unprecedented efficiency of 13.24 % with a JSC of 20.32 mA cm-2, FF 0.78 of and VOC of 0.84 V. The cause is explained by using the results of Hall effect measurement and Mott-Schottkey plot from the view point of carrier concentration, mobility, and built in potential. The carrier diffusion length increased from 88.7 nm, to 348 nm after addition of EAI. This justifies the higher VOC. This agrees with the trend obtained from Hall effect measurement. XPS study proved that by the introduction of EA cation, the oxygen content has been reduced compared to the pristine perovskite film. Tuning the A site cation not only has a significant effect on the crystal stability but also the lattice strain of the perovskites. This work is expected to establish a trend on fabricating tin halide PSCs that is able to compete with lead-based PSCs.

Photovoltaic properties of ITO/p-Si heterojunction prepared by pulsed laser deposition

In this study, indium tin oxide (ITO) was deposited onto sapphire and low resistive p-Si substrates using pulsed laser deposition (PLD) technique. The optical energy gap of ITO deposited on the sapphire substrate was 3.7 eV at room temperature. Photoluminescence (PL) of ITO shows an emission of broad peak at 524 nm. Photovoltaic (PV) characteristics of the n-ITO/p-Si heterojunction are examined and showed conversion efficiency [Formula: see text] of 1.8%. The open circuit voltage [Formula: see text] for this cell was 0.49 V while the short circuit current density [Formula: see text] was 17.4 mA/cm2. The fill factor of this cell was 22%. The ideality factor of ITO/Si heterojunction is about 3.1. The barrier height [Formula: see text] of the heterojunction was determined from I–V characteristics and was 0.83 eV. The responsivity of the heterojunction was measured and the maximum value of responsivity was 0.5 A/W without bias voltage. The minority carrier lifetime of the solar was measured using open circuit voltage decay (OCVD) method and found to be 227 [Formula: see text]s.

Open‐circuit voltage decay: moving to a flexible method of characterisation

Open-circuit voltage decay (OCVD) is a method to characterise minority carrier effective lifetime ( τ eff ). It is non-destructive, simple and low-cost. It has been mainly used in silicon p-n junctions. τ eff is not only a very important parameter to optimise device design but also to supervise process steps. It is not the only parameter we can obtain by OCVD. Due to the intrinsic space charge region capacitance of a p-n junction, the doping level of the lowest-doped region ( N l ) and built-in potential ( V bi ) are extractable. Moreover, it is also possible to obtain the shunt resistance ( R sh ) value when it has a significant effect on the p-n junction behaviour. The authors first applied the well-established one-diode model in a transient regime to simulate OCVD signal. In a second step, they used an optimisation algorithm to fit the experimental curve of a silicon diode to extract τ eff , N l , V bi and R sh . These values were compared to those obtained from C–V and I–V. Results are promising and demonstrate for the first time, the flexibility of the OCVD method. It opens up the perspective for the development of add-on features of the method and for measuring short lifetime.

Open-Circuit Voltage Decay Simulations on Silicon and Gallium Arsenide p-n Homojunctions: Design Influences on Bulk Lifetime Extraction

Open-Circuit Voltage Decay (OCVD) method was investigated for few decades as a simple and convenient method to characterize effective lifetime into Ge and Si p-n homojunctions. Minority carrier lifetime (MCL) is an important parameter to optimize device design where being able to investigate one type of carriers is an important goal. The p-n homojunction design is of major importance to reach that purpose by OCVD. We carried out Technology Computer Aided-Design simulations of the OCVD signal. The study focused on Si and GaAs p-n homojunctions. We looked into bulk thickness and doping level influences on bulk lifetime extraction. Previously, those influences have not been quantified for Si and never investigated for GaAs. MCL accurate extraction from bulk required a bulk thickness at least 4 times higher than diffusion length and emitter doping levels at least 2 orders of magnitude higher than bulk. Likewise, the paper shows different accuracy of extraction between GaAs/Si and p-type/n-type bulk in p-n homojunction.

Temperature dependence of current–voltage and carrier lifetime characteristics in InGaN blue light-emitting diode

In this report, we have measured current–voltage (I–V) and carrier lifetime characteristics of an InGaN-based commercial blue light-emitting diode in a temperature range from 350 to 110 K. Two distinctly different current domains, namely, region I and region II have been identified in I–V dependence. I–V data for region I have been used for the evaluation of ideality factor which varies from 1.478 to 3.932 when the temperature changes from 350 to 110 K. We have also investigated how far the existing models account for our experimental results. From an analysis of the Arrhenius plot of I–V–T curves in terms of the model due to Hirsch and Barriere it is found that the domains are distinguished by current transport mechanisms governed by hole thermionic emission and hole tunneling which are discussed in detail. Next, estimating the data on voltage gradient obtained from the open circuit voltage decay method, as well as those of ideality factor from the I–V measurement, the temperature dependence of carrier lifetime has been evaluated. A logarithmic plot of carrier lifetime as a function of inverse temperature shows a weak temperature-dependence below 228 K and this region gives important information regarding the dominant energy level of traps assisting tunneling of current carriers in the device.

Effective Lifetime Experimental Measurement under External Magnetic Field in Transient Dynamic State Obtained from a Square Electrical Excitation by Open Circuit Voltage Decay Method

In this work, we present an experimental transient 3-Dimensionnal study for the minority charge carriers’ effective lifetime measurement under magnetic field in transient dynamic state. The magnitude of the magnetic field B is varied from 0 mT to 0.03 mT. The method used is mainly based on the open circuit voltage decay method. The solar cell is injected by a low electrical excitation which protects against capacitance effects. Our approach is based on the open circuit voltage decay response analysis. From an experimental set-up, we get the transient voltage data on a digital scope. The data are used for plotting transient voltage decay curves. The curves obtained and analyzed are fitted in their linear zone. This zone presents an ideal decay which permits to get good values of lifetime. The slope of the linear decay is inversely proportional to effective lifetime. The results of fitting permit determinate the effective charge carriers’ lifetime directly. The results obtained are then presented and analyzed. The observations indicate that the charge carriers effective lifetime decrease when the magnetic field increases.

Enhancement of the performance of dye-sensitized solar cells using sensitized zinc oxide nanoparticles by rhodamine B dye

In the present work, ZnO nanoparticles were synthesized via a simple wet chemical (hydrothermal) technique using zinc acetate dihydrate (Zn(CH3COO)2.2H2O) as a row material dissolved into absolute methanol and aqueous NaOH as precipitation agent. The X-ray diffractometer (XRD) patterns showed a standard hexagonal wurtzite structure of ZnO NPs with average particle size of about 28±2 nm. High resolution-transmission electron microscopy (HR-TEM) micrograph of ZnO NPs showed semi-spherical particles with an average size of about 25.3±6 nm, which agreed well with the XRD results. UV-Vis spectrum of the ZnO NPs revealed the highest absorption band at 366.4 nm and the optical energy gap (Eg) was about 3.12 eV. The Photoluminescence spectrophotometer (PL) spectrum emission illustrated lower UV emission than the visible emission. This indicated to the high defect density in ZnO sample. The effect of concentration of cost-effective Rhodamine B dye on the performance of dye-sensitized solar cells) DSSCs) based on ZnO NPs has been studied. The best performance among the five concentrations was 0.7 mM. The photon to electric energy conversion efficiency of the DSSCs has been found to increase by eight times from 0.07 to 0.58 %. Transient open-circuit voltage decay (TOCVD) method has been used to investigate the electron lifetime (τn) and the electron recombination velocity (Krec) in DSSCs, by using the double exponential function. The results revealed that the Rhodamine B dye can be an efficient dye as a low-cost sensitizing dye for DSSCs.

Preparation and Characteristics Study of Polystyrene/Porous Silicon Photodetector Prepared by Electrochemical Etching

Novel doped polystyrene (PS)/porous silicon (PSi) heterojunction photodetector prepared by solution cast and electrochemical techniques is proposed here. The structural and optical properties of polystyrene film and porous silicon surface were investigated using X-ray diffraction (XRD), scanning electron microscope, Fourier transformed infrared (FT-IR), and UV–Vis spectrophotometer. XRD data confirmed that the PS film was amorphous in nature and the porous silicon was nanocrystalline. The optical properties showed that the average optical transmittance and the optical energy gap of PS film were 80% and 3.2 eV, respectively. The electrical properties revealed that the electrical resistivity and mobility of the doped polystyrene film were 3 × 104 Ω cm and 4.5 × 10−5 cm2 V−1 s−1, respectively. Photoluminescence PL of porous silicon was investigated. Dark I–V characteristics revealed that the PS/PSi heterojunctions prepared with an etching time of 5 min exhibited better-rectifying properties than that of PS/PSi heterojunction prepared at 10 min. The figures of merit of the photodetectors such as spectral responsivity, external quantum efficiency, and detectivity were investigated and compared with Au/PSi Schottky photodetectors. Minority carrier lifetime of the photodetectors was measured using open circuit voltage decay method.

Experimental Determination of Effective Minority Carrier Lifetime in HgCdTe Photovoltaic Detectors Using Optical and Electrical Methods

This paper presents experiment measurements of minority carrier lifetime using three different methods including modified open-circuit voltage decay (PIOCVD) method, small parallel resistance (SPR) method, and pulse recovery technique (PRT) onpnjunction photodiode of the HgCdTe photodetector array. The measurements are done at the temperature of operation near 77 K. A saturation constant background light and a small resistance paralleled with the photodiode are used to minimize the influence of the effect of junction capacitance and resistance on the minority carrier lifetime extraction in the PIOCVD and SPR measurements, respectively. The minority carrier lifetime obtained using the two methods is distributed from 18 to 407 ns and from 0.7 to 110 ns for the different Cd compositions. The minority carrier lifetime extracted from the traditional PRT measurement is found in the range of 4 to 20 ns forx=0.231–0.4186. From the results, it can be concluded that the minority carrier lifetime becomes longer with the increase of Cd composition and the pixels dimensional area.

Study of effective carrier lifetime and ideality factor of BPW 21 and BPW 34B photodiodes from above room temperature to liquid nitrogen temperature

In the present work we have studied the temperature dependence of two most important characteristics of the photodiodes (BPW 21and BPW 34B), namely, the ideality factor and the carrier lifetime; both of which are found to change significantly at low temperature. The effective carrier lifetime measured by the Open Circuit Voltage Decay method (OCVD) shows a gradual increase in value from 350K to about 250K then sharply decreases by about thirty percent of its highest value at liquid nitrogen temperature, the trend being similar for both the devices. The dark forward current–voltage characteristics over the same temperature range yield the value of ideality factor which increases nearly by a factor of three for both the photodiodes at the liquid nitrogen temperature. The nature of variation of both the parameters has been qualitatively accounted for in terms of the recent tunneling models. The data generated for the first time for the devices and their broad theoretical understanding will help to improve design and application of the photodiodes, particularly at low temperature.

Comparison between TCAD simulated and measured carrier lifetimes in CMOS photodiodes using the Open Circuit Voltage Decay method

The control and prediction of minority carrier lifetime are crucial for the design of photodiodes, especially for CMOS image sensors, because signal electrons must be captured before recombination. Analytic models have been developed but do not allow accurate and reliable lifetime estimations according to complex photodiode architecture. In this work, we show for the first time that mixed-mode TCAD simulations produce accurate and reliable results for realistic photodiode designs. To arrive at this conclusion, we have performed measurements and simulations on two different photodiodes using the Open Circuit Voltage Decay method.

Optimization of Holding Current in 4H-SiC Thyristors

Two designs (A and B) of 4H-SiC thyristors for pulse power applications were implemented and characterized in this work. Both designs have the same layout and epi-layer stack except for the anode layers: thyristors with design A (baseline) had a thin (~0.5 um) anode while devices with design B (optimized) consisted of a heavily doped cap layer (~0.5 um, ~1019/cc) and ~1.5 um p-type layer with lower doping (~1018/cc). All devices were fabricated in 4” 4H-SiC subSuperscript textstrates (three wafers per each design) and were fully characterized at the wafer level including measurements of forward voltage, blocking voltage, leakage current, and holding current. It was shown that the mean value of the holding current in the thyristors with thin anode was significantly higher (0.7A) than that of the thyristors with thick anode (0.1A), while other parameters had practically the same values. The open circuit voltage decay (OCVD) method was used for measurements of the minority carrier lifetime in order to correlate it with the holding current. Impact of material properties and device design parameters on the holding current is discussed as well.

Reaction Order and Ideality Factor in Dye-Sensitized Nanocrystalline Solar Cells: A Theoretical Investigation

Nonlinear recombination in dye-sensitized solar cells was studied from a fundamental point of view. A model based on Marcus theory was used to describe the recombination from both conduction band and trap states. By combination of this model with the empirical form of nonlinear recombination, dependency of the reaction order (β) on the microscopic parameters of the solar cell was investigated. It was analytically shown that β is always less than unity and also depends on the quasi Fermi-level in semiconductors. By this nonconstant β, the dependency of the ideality factor (m), electron diffusion length (Ln), and the electron lifetime (τn) on the Fermi-level were studied. It was discussed that the nonconstant β can explain the flattening of the Ln at high Fermi-level, as observed in some recent experimental works. For the lifetime, it was shown that only the quantity τn/m is accessible in the common open-circuit voltage decay method. It was also shown that the lifetime and the ideality factor can be obtaine...

A Self-Consistent Model of the OCVD Behavior of Si and 4H-SiC $\hbox{p}^{+}\hbox{-n-n}^{+}$ Diodes

A comprehensive analytical model of the open-circuit voltage-decay (OCVD) response for a generic diode, switched from an arbitrary forward-bias condition, is proposed. To properly account for the steady-state conditions of the diode, the dynamic model incorporates an accurate description of the static <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> curves, which turns also useful for better understanding the influence of physical parameters on voltage transitory. As shown from comparisons with simulations and experiments, the model accurately describes the spatial-temporal variation of carriers and currents along the whole epilayer and allows one to resolve some ambiguities reported in the literature, such as the stated inapplicability of the OCVD method on thick epilayers, the reasons of the observed nonlinear decay of the voltage with time, and the effects of junction properties on voltage transient.

Experimental measurements of majority and minority carrier lifetime profile in SI epilayers by the use of an improved OCVD method

In this letter, the first experimental results of a recently proposed technique for measuring the carrier lifetime profile are presented. The technique makes use of a four-terminal bipolar test structure to electrically define the epilayer volume where recombination occurs and employs the open circuit voltage decay method for lifetime parameters extraction. For the capability of the test structure to depurate measurements from the parasitic ohmic effects, the technique is able to measure the ambipolar and minority carrier lifetime along epilayer at high and low injection levels respectively. Comparisons of measurements with numerical simulations are reported to confirm the validity of the proposed technique.

Open circuit voltage decay lifetime of ion irradiated devices

Open circuit voltage decay method for measuring of excess carrier lifetime is shown to be effective for in-process checking of ion irradiated power diodes. 2.5 kV/100 A P-i-N diodes irradiated by helium ions with different irradiation energies and doses were used for presentation of capabilities of this method. Differences in carrier dynamics during the OCVD process between unirradiated and irradiated devices were studied by use of the device simulation in ATLAS.

Influence of carrier recombination in the space charge region on minority carrier lifetime in the base region of solar cells

In this paper the minority carrier lifetime ( τ) in the base region of an n +/p silicon solar cell is calculated. The open circuit voltage decay method is employed. The influence of carrier recombination in the space charge region is considered through an interface recombination velocity, S i. An analytical expression for τ is obtained and its value for one particular case is reported.