A measurement technique to obtain the recombination lifetime profile in epi layers at any injection level

The measurement technique proposed in [1] to obtain a high injection recombination lifetime profile is extended to any injection level in order to obtain both the majority- and minority-carrier lifetimes as well as its profile along the epi layer. The technique is simulated by numerically solving the relevant equations and the extraction of a varying lifetime profile is demonstrated both at low- and high-injection levels. Some experimental results on n-n⁺epi layers of different doping and thicknesses will be reported to demonstrate the possibilities of this measurement technique, and the extraction of both minority- and majority-carrier lifetime is obtained from the measurements of lifetime as a function of the injection level.     

On the injection level dependence of the minority carrier lifetime in defected silicon substrates

In the literature several reports have indicated a strong increase of the minority carrier lifetime with injection level in defected single crystal and semi-crystalline silicon. These types of potentially low-cost materials are being developed for the photovoltaic industry. The lifetime increase, mainly observed at low injection levels, has usually been explained by the saturation of active traps with increasing injection level. However, a detailed experimental analysis of the recombination losses in materials showing this behavior, points to a strong local variation in the trap density, presumably associated with crystal microdefects. We demonstrate in this paper that the non-linearity of the recombination current at low illuminations observed in defected materials, can be explained by considering the recombination at grain boundaries and microdefects. The conditions are detailed under which the lifetime increases with injection level.     

Thermodynamical analysis of optimal recombination centers in thyristors

The main criterion for an optimal recombination center in thyristors has been reformulated, starting from a basic thermodynamical level. From an extended grand canonical ensemble, statistical expressions for the thermal emission rates of an impurity atom are obtained in terms of changes in enthalpy, electronic and vibrational entropy. The ratio between lifetimes at high and low injection levels is evaluated for single and double level recombination centers and calculated for different enthalpy positions and entropy changes of the center and for different resistivities of the thyristor middle region. It is shown that the expected changes in entropy, when a charge carrier is emitted or captured by the center influences the optimal enthalpy position in silicon by as much as 0.1 eV. Also, a complete change in the influence of injection level on lifetime at standard resistivities and temperature for high power devices is noted. The optimization criterion is compared with experimental data pertinent to thyristor optimization. The paper demonstrates the necessity of making a profound thermodynamical analysis of the charge carrier traffic at a recombination center when using experimental data for deep impurities in the optimization of thyristor lifetime ratings.     

Parametric description of the effect of electron irradiation onrecombination lifetime in silicon layers: an experimental approach

The aim of this paper is to perform an experimental investigation on the effects of electron beam irradiation on the recombination lifetime of both p-type and n-type silicon layers in order to provide a set of parameters useful to model the recombination effects in semiconductor computer simulation package. To this goal, the authors propose to use a proper three-terminal test structure in order to extract these parameters directly from lifetime measurements along the silicon layers at different temperatures and at different injection levels by using the same silicon samples before and after the electron irradiation process in order to highlight the effects of the irradiation itself on the lifetime. The experimental results indicate that the electron irradiation is more effective for controlling the high-injection lifetime in p-type silicon than in an n-type one. The effect of the irradiation on lifetime can be basically taken into account by means of one energy level placed at 0.27 eV below the conduction band edge for both n-type and p-type material, with σ _p≅10 σ_n     

Quantitative model for epitaxial-transistor collector characteristics

A 1-dimensional transistor model is presented which characterises the variation of collector resistance with two parameters. The mode assumes that lifetime varies inversely with injection level. Calculated collector characteristics and hFE against collector-current curves are compared with experimental results.     

Carrier lifetimes in silicon

Carrier lifetimes in semiconductors are being rediscovered by the Si IC community, because the lifetime is a very effective parameter to characterize the purity of a material or device. It has become a process and equipment characterization parameter. The various recombination mechanisms are discussed and the concept of recombination and generation lifetime is presented. We show that surface recombination/generation plays an important role in today's high purity Si and will become yet more important as bulk impurity densities in Si are reduced further. Furthermore, the dependence of lifetime on impurity energy level and minority carrier injection level is discussed. Concepts are stressed in the paper, with the necessary equations to clarify these concepts. Wherever possible, the concepts are augmented with experimental data, with particular emphasis on the case of iron in silicon, because Fe is one of the most important impurities in Si today. We have used Si in the examples because lifetime measurements are most commonly made in Si     

微波光电导衰减法测量N型4H-SiC少数载流子寿命

为了更好地了解N型4H-SiC的电学特性,评价其晶体质量,采用激光技术和微波光电导作为非接触、非破坏性测量半导体特性的一种工具,描述了其测试原理和实验装置,并讨论了不同的激发强度下,其少数载流子寿命的变化。结果表明,改变入射激光能量(即光子注入水平),样品电压峰值与激发强度成正比,对其载流子寿命几乎没有影响。该方法能方便快捷地测量载流子的寿命,对SiC材料性能的研究具有重要意义。     

A theoretical explanation of the carrier lifetime as a function of the injection level in gold-doped silicon

An expression for the recombination rate in gold-doped silicon is derived taking into account both gold energy levels. This formula shows that the dominant energy level under high-injection conditions is not the midgap gold acceptor, but the gold donor level. The high-low injection lifetime ratio calculated with the derived expression is in good agreement with measured values. This indicates that lifetime and capture cross section measurements are consistent with each other. The relation between gold concentration and high-injection lifetime is calculated. The relative density of the neutral and the negatively and positively charged traps is shown as a function of the carrier injection level.     

Experimental verification of the Shockley?Read?Hall recombination theory in silicon

The dependence of carrier lifetime on injection level has been measured in silicon power devices. As examples, the results of an Au-doped and an as-processed, not intentionally doped, specimen are given. The experimental results confirm the Shockley?Read?Hall recombination theory. The ratio of the capture cross-sections of the holes and electrons is calculated.     

The Influence of Parasitic Effects on Injection-Level-Dependent Lifetime Data

A circuit simulation approach is employed to investigate the influence of various parasitic effects on injection-level-dependent lifetime data of samples containing p-n junctions. Simulations of the influence of shunts, localized recombination, edge recombination, and a combination of these on lifetime data are presented. The simulation shows that the nature of the parasitic effects can be qualitatively identified due to their different lifetime behaviors at various injection levels. It is demonstrated that the parasitic effects start to dominate the lifetime data at injection levels , and the lifetime behavior can look similar to Shockley-Read-Hall recombination in some cases. A range of case studies with experimental data and data fitting are presented. The case studies show that parasitic effects can interfere with lifetime-based experiments. In some cases, the understanding of the influence of parasitic effects leads to a reinterpretation of the lifetime behavior of the test devices.     

Realistic efficiency potential of next‐generation industrial Czochralski‐grown silicon solar cells after deactivation of the boron–oxygen‐related defect center

We measure carrier lifetimes of different Czochralski‐grown silicon (Cz‐Si) materials of various boron and oxygen concentrations and determine the maximum achievable lifetime after an optimized thermal treatment. We obtain very high and stable bulk lifetimes of several milliseconds, virtually eliminating the boron–oxygen (BO) defect complex, which previously limited the carrier lifetime in boron‐doped Cz‐Si materials after prolonged illumination. Based on these experimental results, we introduce a new parameterization of the bulk lifetime of B‐doped Cz‐Si after permanent deactivation of the BO center. Notably, we measure lifetimes up to 4 ms on 2‐Ωcm Cz‐Si wafers at an injection level of 1/10 of the doping concentration. Importantly, these high lifetime values can be reached within 10 and 20 s of BO deactivation treatment. A detailed analysis of the injection‐dependent lifetimes reveals that the lifetimes after permanent deactivation of the BO center can be well described by a single‐level recombination center characterized by an electron‐to‐hole capture cross‐section ratio of 12 and located in the middle of the silicon band gap. We implement the novel parameterization into a two‐dimensional device simulation of a passivated emitter and rear solar cell using technologically realistic cell parameters. The simulation reveals that based on current state‐of‐the‐art solar cell production technology, efficiencies reaching 22.1% are realistically achievable in the near future after complete deactivation of the BO center. Copyright © 2016 John Wiley & Sons, Ltd.     

Application of the equivalent circuit model for semiconductors to the study of Au-doped p-n junctions under forward bias

The Green-Shewchun method of solution is applied to the transmission line circuit model of Sah to obtain the forward current-, capacitance-, and conductance-voltage characteristics of semiconductor p-n junctions. Numerical solutions are obtained for diffused dopant impurity profiles and several position dependent concentration profiles of gold recombination centers to illustrate the variation of the reciprocal slope parameter m in the dc current, exp (qV/mkT). A new behavior of m = 2 is observed for many decades of current in the low-level range when the recombination centers are concentrated at the edge of the space-charge layer as expected from ion implantation. The theoretical calculations are compared with experimental forward current-, conductance-, and capacitance-voltage data from 10 to 10⁶Hz and 77 to 300 K. Excellent agreements are obtained without adjustable parameters for boron and gold diffused p⁺-n silicon diodes from low to high injection levels. A twenty-five fold increase of the steady-state hole lifetime from low to high injection level is both observed and predicted. Agreements are also obtained for phosphorus- and gold-diffused n⁺-p silicon diodes from low to intermediate injection levels where the steady-state electron lifetime is nearly constant and controlled by electron capture into the positively charged gold donor centers.     

Recombination and trapping in multicrystalline silicon

Minority carrier recombination and trapping frequently coexist in multicrystalline silicon (mc-Si), with the latter effect obscuring both transient and steady-state measurements of the photoconductance. In this paper, the injection dependence of the measured lifetime is studied to gain insight into these physical mechanisms. A theoretical model for minority carrier trapping is shown to explain the anomalous dependence of the apparent lifetime with injection level and allow the evaluation of the density of trapping centers. The main causes for volume recombination in mc-Si, impurities and crystallographic defects, are separately investigated by means of cross-contamination and gettering experiments. Metallic impurities produce a dependence of the bulk minority carrier lifetime with injection level that follows the Shockley-Read-Hall recombination theory. Modeling of this dependence gives information on the fundamental electron and hole lifetimes, with the former typically being considerably smaller than the latter, in p-type silicon, Phosphorus gettering is used to remove most of the impurities and reveal the crystallographic limits on the lifetime, which can reach 600 μs for 1.5 Ωcm mc-Si. Measurements of the lifetime at very high injection levels show evidence of the Auger recombination mechanism in mc-Si. Finally, the surface recombination velocity of the interface between mc-Si and thermally grown SiO₂ is measured and found to be as low as 70 cm/s for 1.5 Ωcm material after a forming gas anneal and 40 cm/s after an anneal. These high bulk lifetimes and excellent surface passivation prove that mc-Si can have an electronic quality similar to that of single-crystalline silicon     

Injection and doping dependence of SEM and scanning light spot diffusion length measurements in silicon power rectifiers

SEM electron beam-induced current (EBIC) and light spot scanner photocurrent (PC) versus distance characteristics recorded from silicon power rectifiers were observed to vary consistently with beam power over the range 0.1 μW to 1 mW. To interpret these results, existing theory has been extended to incorporate a minority carrier lifetime which varies with position, doping and injection level. A simple procedure was devised to take surface recombination into account; under these conditions good agreement was obtained between theory and experiment. In the diffused end regions the results were best explained by a lifetime which varied with doping at $\text{N}{}_{\mathrm{d}}{}^{\mathrm{<mtext>?(</mtext><mtext>1</mtext><mtext>2</mtext><mtext>)</mtext>}}$. The variation in shape with increasing beam power could be understood on the basis of an injection dependent surface recombination velocity. In the base, it was necessary to consider injection dependent effects both in the bulk and at the surface to explain the observed characteristics. We conclude that EBIC/PC techniques, while excellent for measuring surface recombination velocity and low level lifetime, are less satisfactory at higher levels. The wide range of injection levels produced by an electron probe or laser light spot makes the analysis rather uncertain. The techniques do, however, provide a good method for assessing lifetime in power devices and, suitably interpreted, can provide useful information about the way lifetime varies with injection level. Taking surface recombination into account is absolutely essential if valid results are to be obtained.     

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.     

Triplet-induced degradation: An important consideration in the design of solution-processed hole injection materials for organic light-emitting devices

Solution-processed organic light-emitting devices (OLEDs) still require improvements in their operational lifetime in order for them to become commercially viable. One factor that limits the lifetime of these devices is the instability of the hole injection layer (HIL). Therefore, understanding its degradation mechanism is crucial for the development of more stable solution-processed OLEDs. In this work, we use an archetypal fluorescent OLED in conjunction with an experimental solution-processed HIL in order to elucidate the degradation mechanism in these HILs. Our studies show that degradation is caused by triplet excitons. This new triplet-induced hole injection degradation is expected to be a common phenomenon in OLEDs, and therefore should have important implications for the design of stable HILs.     

Impact of the injection‐level‐dependent lifetime on Voc,FF, ideality m,J02, and the dim light response in a commercial PERC cell

The injection‐level‐dependent (ILD) lifetime of the silicon wafer impacts many characteristics of the final photovoltaic cell. While efficiency is commonly understood to be impacted by the silicon bulk lifetime (at the maximum power point injection level), this work demonstrates the wide ranging impacts of ILD lifetime on the V_oc, the fill factor (FF), the diode ideality factor m, and the dim light response. Instead of a two‐diode model, we utilize a boundary + ILD bulk lifetime model to analyze a commercial passivated emitter rear contact (PERC) cell featuring an AlO_x dielectric rear passivation. The ILD lifetime is directly measured and used to calculate the bulk recombination current across injection levels. With this boundary + ILD lifetime model, we demonstrate the role of the ILD lifetime on many cell parameters in this PERC cell. For most high efficiency commercial p‐type monocrystalline solar cells, the typically lower bulk lifetime at the maximum power point versus the lifetime at the open circuit point reduces the measured FF and pseudo‐FF. This work illustrates that for a commercial PERC cell with AlO_x rear passivation, the ILD lifetime is the primary mechanism behind reduced FF, ideality factors greater than 1, and the source of the J₀₂ term in the two‐diode model. The crucial implications of this work are not only to better understand commercial PERC cell loss mechanisms but also to encourage a focus on different metrics in cell diagnostics. One such metric is the V_oc at 0.1 or 0.05 suns. Copyright © 2016 John Wiley & Sons, Ltd.     

Temperature dependence of the lasing characteristics of the 1.3 µm InGaAsP-InP and GaAs-Al0.36Ga0.64As DH lasers

We report here our experimental observations on the temperature dependence of threshold current, carrier lifetime at threshold, external differential quantum efficiency, and gain of both the 1.3 μm InGaAsP-InP and GaAs-AlGaAs double heterostructure (DH) lasers. We find that the gain decreases much faster with increasing temperature for a 1.3 μm InGaAsP DH laser than for a GaAs DH laser. Measurements of the spontaneous emission observed through the substrate shows that the emission is sublinear with injection current at high temperatures for the 1.3 μm InGaAsP DH laser. Such sublinearity is not observed for GaAs DH lasers in the entire temperature range 115-350 K. The experimental results are discussed with reference to the various mechanisms that have been proposed to explain the observed temperature dependence of threshold of InGaAsP DH lasers. We find that inclusion of a calculated nonradiative Auger recombination rate can explain the observed temperature dependence of threshold current, carder lifetime at threshold, gain, and also the sublinearity of the spontaneous emission with injection current of the 1.3 μm InGaAsP-InP DH laser. Measurement of the nonradiative component of the carrier lifetime (τA) as a function of injected carrier density (n) shows thattau_{A}^{-1} sim n^{2.1}which is characteristic of an Auger process.     

Hot-electron-induced punchthrough (HEIP) effect in submicrometer PMOSFET's

Degradation of device characterisitics due to hot-carrier injection in submicrometer PMOSFET has been investigated. We found that in submicrometer p-channel transistors the punchthrough voltage is seriously reduced due to hot-electon-induced punchthrough (HEIP). A worst case analysis of the experimental data shows substantially reduced lifetime due to HEIP.     

The implementation of temperature control to an inductive‐coil photoconductance instrument for the range of 0–230°C

A new device setup for temperature and injection‐dependent lifetime spectroscopy (TIDLS) is described. It comprises two off‐the‐shelf components: a heating and cooling stage (HCS) from INSTEC and an inductive‐coil photoconductance (PC) instrument (WCT‐100) from Sinton Consulting Inc. The HCS was fitted to the WCT‐100 in a manner that circumscribes the inductive coil (the sensor) of the RF bridge circuit and controls the temperature of the wafer effectively. This setup has the advantage of requiring minor modifications to industry standard instruments while attaining a large temperature range. As experimental verification, injection‐dependent lifetimes were measured over a temperature range, 0–230°C, in three iron‐implanted silicon wafers. The measured lifetimes are consistent with the Shockley–Read–Hall equation using the impurity concentration calculated from the implant dose and the energy level and capture cross‐sections of interstitial iron from the literature. Copyright © 2008 John Wiley & Sons, Ltd.