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We have obtained a simple expression that determines the effective minority carrier lifetime in macroporous silicon with periodic arrangement of infinitely long macropores as a function of bulk lifetime, surface recombination velocity of minority carriers, pore radius and the distance between the centers of macropores. This expression can be applied also to macroporous silicon with randomly distributed pores by replacing the pore radius and the distance between the centers of macropores with their average values. The distribution of steady-state excess minority carriers in macroporous silicon is calculated for the analytical model proposed by us. The calculation is made for the case when both the outer surface of macroporous silicon and the bottom of pores are illuminated with light. We observed two peaks of the distribution of steady-state excess minority carriers in macroporous silicon near the surfaces illuminated with light of wavelength 0.95 m. At the same time, if macroporous silicon was illuminated with light with the wavelength of 1.05 μm, we observed only one maximum in the distribution function of the excess minority carriers, in spite of the fact that the pore bottom was also illuminated with light. It is shown that the distribution of excess minority carriers in macroporous silicon with through pores is similar to the distribution in single crystal silicon. But in this case, the effective lifetime of minority charge carriers in the effective medium of macroporous silicon, which includes silicon and the surface of pores, corresponds to the bulk minority-carrier lifetime in monocrystalline silicon.

The voltage and current oscillations occasionally occur during the reverse recovery transient of the superjunction MOSFET body diode. This paper identifies the unique reverse recovery oscillation characteristics of the superjunction MOSFET body diode. Base on the experimental investigation and theoretical analysis, the various reverse recovery oscillation mechanisms are clarified. At first, with a discrete 650 V/47 A superjunction MOSFET utilized, the high-frequency and low-frequency oscillation characteristics during the reverse recovery transient are obtained by the double-pulse test. After the theoretical analysis, it is found that the superjunction MOSFET body diode has various oscillation mechanisms depending on its drift region injection level. Under high-level injection condition, the high-frequency oscillation occurs due to the plasma extraction transient-time (PETT) effect. Under low-level injection condition, the body diode’s snappy reverse recovery results in the low-frequency LC oscillation. In the end of the paper, the oscillation behaviors under both high and low level injection conditions are reproduced by the mixed-mode numerical simulation, the simulation results validate the proposed oscillation mechanisms.

This paper presents an application of computational electromagnetics (CEM) and low level injection techniques to determine the electrical transients that may appear in an aircraft wiring during a lightning strike. The study was accomplished in four steps: first, the main electromagnetic coupling mechanisms to a specific sensor interface and its interconnecting cables were identified and characterized in the test bench; then an electromagnetic model was developed to support the understanding of the coupling problem. The knowledge attained from this experiment was further applied to develop a realistic numerical model intended to represent the aircraft installation and its predictions were validated against the actual transient levels obtained from the full aircraft test. As the final step, a design modification was proposed and evaluated.

In this work, we have investigated the impact of interstitial Fe contamination on the effective minority carrier lifetime of n-type Cz silicon bulk material for high efficiency solar cells. The study covers a Fe concentration in the silicon bulk from 3.5 × 1012 cm-3 to 2.7 × 1014cm-3. We have added 5 different concentrations (30, 100, 300, 1000 and 3000 ppb) of Fe intentionally to a wet chemical process tank and measured the transfer to the silicon wafer surface mimicking a possible contamination during wet chemical processing. In order to fabricate carrier lifetime test vehicles, the silicon wafer is then passivated with thermal silicon oxide from both sides. The surface contamination is driven into the bulk by mimicking a high temperature process during solar cell manufacturing. Effective minority carrier lifetime is measured at injection levels from 1 × 1013 cm-3 to 3 × 1015cm-3. We have fitted the theoretical curve for interstitial Fe derived from the SRH theory to the measured values and extracted the Fe contamination concentration. This value is comparable to the calculated value extracted from the surface contamination measurement. For low level injection (LLI), we extracted the capture cross section for interstitial Fe to be 6.45 × 10-17 cm/s ± 2.23 × 10-17 cm/s. The measured Fe contamination levels are used for the conversion efficiency fitting of a n-type bifacial silicon solar cell using QUOKKA simulations. The simulations show that very low Fe contamination concentrations of [Fe]bulk = 3.5 × 1012 cm-3 ([Fe]surf = 6 × 1010cm-2) already degrade the solar cell efficiency by 10% relative.

This paper reports on the effect of screen printed metallization on passivation quality of TOPCon structure. A metallized TOPCon using fire-through screen printing process showed excellent saturation current density (metallized J0,TOPCon ~ 15 fA/cm2) with very low contact resistance (~6 mohm-cm2), However, screen printed metallization increased the recombination at low level injection level (≤0.1 sun) causing some degradation in iFF. We successfully fabricated 20.1 % bifacial n-type PERT cells with ∼180 ohm/□ implanted B emitter and TOPCon rear using screen printing and fire through contact technology. Detailed cell analysis showed that high series resistance and saturation current density of metallized B emitter limited the cell performance to ~20%.

A model consisting of Shockley Read Hall (SRH) recombination under steady state conditions of constant photon injection is proposed in this work to study the steady state minority carrier lifetime in CdS/CdTe thin film solar cells. The SRH recombination rate versus optical injection level is analytically approximated in the junction and neutral regions. In the neutral region, it is found that the recombination rate through certain defect levels has one constant value under lower optical injection conditions and another constant value under higher optical injection conditions with the transition occurring at a critical optical injection level. By simultaneously solving the equations of charge neutrality, charge conservation and SRH recombination in the neutral region, it is found that the compensation of doping and the reduction of minority carrier lifetime by donors in the p-type semiconductor can each be remedied by optical injection. It is also demonstrated that this optical-dependent SRH recombination is significant in large bandgap thin films. The measured minority carrier diffusion length in a CdS/CdTe solar cells, as determined from the steady-state photo-generated carrier collection efficiency, shows the predicted transition of minority carrier lifetime versus optical injection level. A numerical fitting of the indirectly-measured minority carrier lifetime by assuming the minority carrier mobility gives a non-intuitive picture of the p–n junction with a low free hole concentration but a narrow depletion region width.

Doping allows us to control the majority and minority charge carrier concentration in organic field-effect transistors. However, the precise mechanism of minority charge carrier generation and transport in organic semiconductors is largely unknown. Here, the injection of minority charge carriers into n-doped organic field-effect transistors is studied. It is shown that holes can be efficiently injected into the transistor channel via Zener tunneling inside the intrinsic pentacene layer underneath the drain electrode. Moreover, it is shown that the onset of minority (hole) conduction is shifted by lightly n-doping the channel region of the transistor. This behavior can be explained by a large voltage that has to be applied to the gate in order to fully deplete the n-doped layer as well as an increase in hole trapping by inactive dopants.

A comparative investigation of γ-ray total dose ionization damage at high and low-level injection (HLI/LLI) for different dose rate irradiation in double polysilicon self-aligned bipolar NPN transistors is presented. The transistors reveal anomalous dose rate radiation responses for Emitter-Base (E-B) electrical field strength in forward active mode. This effect is probably associated with the different types of radiation induced defects, which depends on the E-B junction electric field strength, play the key role to the increase of excess base current.

We verify a fast and simple analytical model for locally contacted rear surface passivated solar cells by three dimensional numerical simulations. For low level injection conditions the analytical model shows good agreement with the numerical results. For intermediate injection levels and for the injection dependent bulk lifetime in oxygen contaminated silicon, the present analytical model deviates from the numerical results. The accordance clearly improves when including injection dependent recombination and conductance in the analytical model. For intermediate to high injection levels, it is crucial to implement additional corrections for injection effects, being emphasised by the low recombinative front side and bulk material of the device structure investigated in this work. When accounting for these deviations from low level injection, analytical modelling turns out being a fast way to predict the optimum contact spacing as well as the electrical parameters of locally contacted rear surface passivated solar cells even for intermediate injection conditions

Double side collecting silicon solar cells such as the emitter wrap through and the both sides contacted and collecting concept are one possibility to maintain high efficiencies even on low lifetime material. To investigate the intrinsic advantages and limitations of this concept we use the solution of the continuity equation under low level injection conditions for a double side collecting (n + pn + ) and a single side collecting (n + pp + ) solar cell. In general, compared to the single side collecting structure, the double side collecting structure yields the highest advantages concerning the roduct of the short circuit current density and the open circuit voltage Jsc·Voc on highly doped material with diffusion lengths in the range of half the cell thickness. A realistic calculation of the fill factor of such devices is done using two dimensional numerical simulations. It is shown that a major reduction of the fill factor is caused by laterally varying voltage induced non-generation losses and ohmic losses, both caused by the majority carrier flow in the base. Electro- and photoluminescence images verify and illustrate the lateral voltage distribution under different illumination levels and terminal voltages.

Exact expressions for the out of phase modulated photocurrent (MPC), the so-called Y signal, with a clear physical insight for density of states (DOS) spectroscopy are derived without any approximation. It is found that, apart from the capture rate of the majority carriers into the probed gap states, additional mixed contributions from the recombination processes of the free majority carriers with trapped minority carriers may be important for the Y signal of lower frequencies. These additional contributions prevent the extraction of a reliable DOS. They become important as long as the capture coefficient for the majority carriers of the recombination centers, where the minority carriers are trapped, is comparable to or higher than that of the recombination centers were the majority carriers are trapped. In this case, the recombination rate is relatively high and the mixed contributions from the recombination processes can be detectable in the experimental Y signal and may also induce a phase lead. Taking...

Electrical characteristics and neutron dosimetry properties of silicon based p-i-n diodes are presented in support of the applications in the sensors for beam monitoring and medical physics. Both the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of silicon planar p-i-n diode sensors with cylindrical geometry have been theoretically modeled and experimentally measured. The shifts of the forward and reverse diode characteristics of the sensors versus the neutron dose have been obtained. It is shown that the neutron irradiation caused shift of the forward voltage of the p-i-n diodes is proportional to the current at which it is measured in the case of the low level injection or to the square root of the current in the case of the high level injection. The C-V characteristics and the full depletion voltages of the diodes have been estimated and experimentally verified. It is shown that the sensitivity of planar cylindrical structures as neutron sensors can be optimized by the selection of the device geometry and the current at which the measurement is performed.

The dark current density in any minority carrier detector architecture is determined by the thermal generation rate per unit volume, Jd ¼ qGtht ¼ qNmint/t, where Nmin is the equilibrium density of minority carriers in the detector volume under consideration, and t is the associated minority carrier lifetime. t is the dimension of the volume, which, in a well-designed detector, is both

The reliability of high-speed SiGe:C HBT under electrical stress close to the Safe Operating Area (SOA) limit is analyzed and modeled. A long time stress test, up to 1000 h, is performed at bias conditions chosen according to applications targeted for these transistors. During the aging tests, Gummel plots are measured at fixed time to analyze the evolution of base and collector current. At low level injection, we observed an increase of the base current whereas the collector current remains constant for the whole Vbe range and during the 1000 h aging time. By means of 2D TCAD simulations, this evolution of base current is attributed to trap activity at the emitter-base junction periphery. Based on TCAD simulation results, we propose an aging law using a differential equation that has been implemented in HiCUM L2 v2.33. This reliability-aware compact model allows designers creating reliability-aware circuit architectures at an early stage of the design procedure, well before real circuits are actually fabricated. � 2015 Elsevier Ltd.

A one-dimensional analytic model describing the motion of minority carriers against the electric field direction under the conditions of high injection level is developed. The results of the model can also be used to estimate the motion of carriers against the field in the case of an arbitrary injection level. The model makes it possible to describe, in good agreement with the results of computer simulation, the modulation of the collector layer resistance in a high voltage SiC bipolar transistor.

In this work, we have decoupled the radiative and nonradiative contributions to recombination by developing analytical models to fit observed non-monoexponential photoluminescence decay and bulk-lifetime temperature-dependence, which has enabled absolute measurement of the effective radiative efficiency and characterization of the dominant defect in lightly doped GaAs samples grown using molecular-beam-epitaxy. The measured effective radiative efficiency values under low level injection conditions range from (88.9 ± 0.1)% and (81.2 ± 0.1)% at 77 K to (0.028 ± 0.001)% and (0.034 ± 0.001)% at 700 K, with 300 K values of (17.3 ± 0.1)% and (10.5 ± 0.1)% in the p-type and n-type samples, respectively. A common defect-signature is observed in the temperature-dependence of the nonradiative lifetime in samples of both doping types, and our measured parameters are consistent with characteristics previously measured for the EL2 defect using deep-level transient spectroscopy.

Although in CdS/CdTe thin film solar cells, experiments showed that the minority carrier lifetime depends on excess carrier concentration, it is not known that under steady state how the lifetime is affected by the defects. High defect concentration in CdS/CdTe solar cells violates the assumption needed to simplify of the Shockley Read Hall (SRH) recombination equation. Also, with high defect concentrations and thus short carrier lifetime, the excess carrier concentration under illumination can be equivalent to or even lower than the defect concentrations. By simplifying SRH equation considering high defect concentration, it is found that in neutral region, the lifetime is excess carrier dependent. By simultaneously solving the equations of charge neutrality, charge conservation and SRH recombination in the neutral region, the minority carrier lifetime as a function of generation rate can be calculated. The measured minority carrier diffusion length in a CdS/CdTe solar cell, as determined from the steady-state photo-generated carrier collection efficiency, shows the predicted transition of minority carrier lifetime versus optical injection level. A numerical fitting of the indirectly-measured minority carrier lifetime by assuming the minority carrier mobility gives a non-intuitive picture of the p-n junction with a low free hole concentration but a narrow depletion region width.

Silicon samples of various doping concentrations have been irradiated with MeV ions at low doses and different temperatures. Deep level transient spectroscopy (DLTS) has been used to characterise the distributions and productions of the divacancy center (V 2 ) and the vacancy-oxygen complex (VO). These two defects have been identified as being responsible for the charge carrier lifetime reduction. Due to their bandgap position and capture cross sections the singly negative charge state of the V 2 controls the low level injection lifetime, but the influence of VO becomes stronger for higher injection levels. The relative abundance of the two defects can be affected by using heavier ions than protons and electrons, which are commonly used today in the fabrication of silicon power devices. The reason for this is that the production of V 2 is enhanced by larger collision cascades, in comparison to VO, following heavier ion implantation. It will be shown that irradiation with heavy ions, instead of protons and electrons, will result in a better relationship between the high and the low level lifetime. This effect can be taken advantage of to improve the trade off between switching time and conduction losses in power devices. It will also be shown that the concentration ratio VO/V 2 can be further improved if the irradiations are performed at lower temperatures than room temperature.

We have extensively measured and analyzed the current mismatch of a small-size n-channel MOS transistor of 2 /spl mu/m/spl times/2 /spl mu/m operated in weak inversion with its p-well-to-n/sup +/-source junction forward and reverse biased. The case of slightly forward biasing the well-to-source junction represents the action of a gated lateral bipolar transistor in low level injection. The measured dependencies of the mismatch in weak inversion on the back-gate forward and reverse biases have been successfully reproduced by a new simple statistical model. From the experimental data, we suggest that i) subthreshold circuits should be carefully designed for suppression of mismatch arising from back-gate reverse bias, and ii) a gated lateral bipolar action in low level injection may be utilized as a new method of improving the transistor matching.

Injection dependent lifetime spectroscopy (IDLS) was performed to identify the type and concentration of the defects associated with metal impurities in crystalline silicon wafers. Minority carrier lifetimes in intentionally contaminated silicon wafers using various metal concentrations were measured by a transformer-coupled, radio frequency-based photo conductance measurement tool, GLM™ 2000. Lifetimes in the bulk of the silicon wafers were measured at low injection level using a square pulse cycle of light with half period > 10 milliseconds to ensure steady state photoconductance was reached. Analysis of the data using Shockley-Read-Hall theory demonstrates the ratio of capture cross-section of electrically active defect level associated with molybdenum (Mo) and copper (Cu). Concentrations (N t ) of electrically active defect states associated with Mo and Cu impurity are determined from measured bulk lifetime at low level injection, using Shockley-Read-Hall carrier concentrations (n 1 and p 1 ), and known activation energy levels (E t ) of the identified metal from the literature.

The passivation mechanisms and qualities of Al2O3, SiNx, SiO2 and a-Si:H( i ) on p - and n -type silicon are investigated by quasi-steady-state photoluminescence measurements. This technique allows effective lifetime measurements in an extremely large injection range between 1010 cm-3 and 1017 cm-3. The measurements are discussed focusing on injections below 1012 cm-3 in order to determine the most effective passivation layer for solar cells arranged for indoor applications. Fixed negative charges in the passivation layer cause field-effect passivation due to band bending leading to either accumulation or inversion at the passivation layer/silicon interface. Accumulation causes a stable passivation quality at low level injection. Inversion leads to effective lifetime losses similar to the losses in the space charge region. On p -type silicon the most effective surface passivation at low injections is provided by Al2O3 or a-Si:H( i ). The n -type silicon samples passivated with a-Si:H( i ) show the best effective lifetimes. SiNx and SiO2 show lifetimes one order of magnitude below a-Si:H( i ). Al2O3 on n -type is the most effective passivation at high injections around 1015 cm-3. Due to inversion losses at low level injections the passivation quality decreases more than two orders of magnitude for injections around 1010 cm-3.

Using numerical simulations, we study the combined effects of minority carrier lifetime and carrier density variation, that is observed in actual CdTe solar cells, on device performance. High open-circuit voltage (V oc ) requires high built in potential as well as low recombination rate in the space-charge region (SCR). Therefore, in a uniformly doped device, maximum open-circuit voltage will be obtained for high carrier density and high lifetime. The fill-factor (FF) is mainly dependent on the minority carrier lifetime. In a case of a highly defective absorber with high carrier density, the SCR is narrow in forward bias and some of the photogeneration occurs outside of the SCR. When the diffusion length is short, these carriers are likely to recombine before being collected, thus creating voltage dependent collection, and FF decrease. For a low carrier density, on the other hand, the electric field strength in the SCR is low enough, that for low lifetimes recombination is a competitive process to drift. This again reduces the FF for low lifetimes. Simulations predict that it is possible to increase the device efficiency for lower carrier density, 1013–1014 cm−3, if the back of the absorber is highly doped. This configuration increases the built in potential and the electric field close to the junction region. In addition, a device with such a doping profile is very tolerant towards the minority carrier lifetime of the highly doped layer. Our simulations show that efficiencies greater than 18% are possible using high doping at the back of the absorber. In contrast, when the absorber properties are uniform, efficiencies >18% require unrealistic doping and lifetime values.

The device is pumped with an electrical current injection. The magnitude of carrier density in QD is higher than in QW since it is the summation of carrier densities in all groups of dots. The corresponding output remains minimal until the carrier concentration in the QD states reaches threshold and then increases rapidly which reduces the carrier density and carrier density rises again through recovery of carriers from current injection. This cycle repeats several time until steady state is achieved. The probability of carrier concentration in the QD states is shown in Fig. 2. The carriers occupy the lower energy states first as their probability being highest then drops all the way with the increase of energy. Once the current reaches the threshold, we can observe a “hole” near central energy, which is known as the spectrum hole burning (SHB) and this SHB becomes more significant with more current injection.

The main objective of this paper is to show that majority carrier current needs to be taken into account in determining base transit time. In previous analytical works for base transit time, majority carrier current in the base was neglected. In this paper both drift and diffusion currents for electron and hole are considered in obtaining minority carrier profile n(x). In the model, it is assumed that the lateral injection of base current into the active base region is occurred from a source function, g. The energy-bandgap-narrowing effects due to heavy doping, velocity saturation as well as doping and field dependent mobility are considered.

In this work the current versus voltage data of a p-n+ junction is converted into minority carrier lifetime data. Space charge recombination currents dominate at modest reverse bias at 80K and taking the dominant recombination centers to be located at the intrinsic Fermi level, the lowest minority carrier lifetime τ0 is determined to be 35ns. This single Shockley-Read-Hall carrier recombination parameter provides an excellent fit to the data over temperature range 40K≤ T≤ 130K; the 35ns minority carrier lifetime also explains the quantum efficiency data. The transition from diffusion to space charge currents occurs for temperatures, T ≤ 100K. For T≤ 40K trap assisted tunneling is the dominant current component. Based on imaging system requirements to be near background limited for photon flux ≈ 1015 ph/cm2-s and detector temperature of 80K, the minority carrier lifetime will need to be increased by one order of magnitude.

Sidegating in GaAs metal‐semiconductor field‐effect‐transistors (MESFETs) is widely attributed to space‐charge‐limited (SCL) conduction through the semi‐insulating (SI) substrate. But often sidegating is accompanied by low sidegate currents and occurs at sidegate voltages that are too small to initiate SCL conduction. We suggest that this is due to low‐level hole injection from a MESFET into the substrate. An analytical treatment of carrier, field, and potential distribution in a SI substrate under conditions of low‐level injection shows that an electric field overshoot may develop in the vicinity of the MESFET when hole injection occurs. This results in a large portion of the applied voltage being dropped across the channel‐substrate interface and, consequently, in sidegating. One result for short structures is the electric field outside the narrow region of overshoot is below the value expected for ohmic conduction. Consequently, over a wide range of applied voltages the field in most portions of the structure is below the critical value required for intervalley electron transfer.

The carrier recombination rates in semiconductor quantum wells are found to be structure dependent. Under high levels of excitation they generally do not follow the recombination rule of the bulk material. Through a differential carrier-lifetime measurement in the strained-layer InGaAs/GaAs quantum wells, it is shown that in quantum wells with lower potential barrier or thinner well width, the recombination rates are smaller due to a larger portion of the injected carriers populating the confinement layers where the carriers recombine more slowly owing to dilute carrier volume density. >

For scavenging energy out of the environment, it is very important for solar cells to maintain the efficiency at low light intensity levels. The high efficiency p-type front junction (18.3% at 1 sun AM1.5) and n-type rear junction (17.3% at 1 sun AM1.5) cells are prepared using an identical cell process based on firing an aluminum paste on the rear. The Al paste acts either as back surface field or rear emitter respectively. A detailed characterization of these cells under low illumination conditions was carried out based on the measured efficiency and suns-V oc . In this paper, it is experimentally and theoretically shown that n-type base cells outperform p-type base cells at such low injection levels. The observed dependence of the performance on the injection level is explained using the Shockley-Read-Hall recombination model where the different capture cross sections for electrons and holes has a decisive influence on the minority carrier bulk lifetime for p-type silicon under low level injection.

In the analysis, the full-range transient response of the gate is calculated using closed-form analytical expressions. This is achieved by generalizing and improving the method used by J.M.C. Stork (IEDM Tech. Dig., p.550, 1988) for the determination of the propagation delay. The proposed model is applicable at low-level injection, unity fan-in, and unity fan-out. The delays related to the transit time, the load, and the junction capacitances are considered. For ECL gates, the emitter follower delay is also included. Various delays (risetime, propagation delay, etc.) calculated using the proposed model agree perfectly with the results of SPICE computer simulations and with the reported experimental values. >

Measured minority and majority carrier mobility temperature dependencies in heavily doped n- and p-GaAs are compared. Majority carrier mobilities in heavily doped GaAs are essentially temperature ~T! independent while minority carrier mobilities exhibit a roughly 1/T dependence. Majority carrier freezeout, which reduces both majority–minority carrier and ionized impurity scattering, is shown not to be responsible for the 1/T minority carrier mobility dependence. The difference in minority and majority carrier mobility T dependencies is explained in terms of the increased degree of degeneracy of majority carriers with decreased temperature, which decreases majority–minority carrier scattering.

We carry out a self-consistent analytical theory of unipolar current and noise properties of metal-semiconductor-metal structures made of highly resistive semiconductors in the presence of an applied bias of arbitrary strength. By including the effects of the diffusion current we succeed to study the whole range of carrier injection conditions going from low level injection, where the structure behaves as a linear resistor, to high level injection, where the structure behaves as a space charge limited diode. We show that these structures display shot noise at the highest voltages. Remarkably the crossover from Nyquist noise to shot noise exhibits a complicate behavior with increasing current where an initial square root dependence (double thermal noise) is followed by a cubic power law., Comment: 10 pages, 8 figures. Accepted for publication in Journal of Applied Physics (Scheduled 1 January 2003)

The increase in the effective carrier lifetime of oxidized p-type silicon at low carrier injection levels is studied from the viewpoint of silicon surface effects. The effective carrier lifetime is measured by a microwave photoconductive decay method. A gold/oxide/silicon structure is used to examine the dependence of effective carrier lifetime on injected carrier concentration. The effective carrier lifetime is measured at various voltages applied between the gold electrode and the silicon substrate in order to change the silicon surface conditions, i.e. accumulation, depletion or inversion. Increase in the effective carrier lifetime at low carrier injection levels is observed only when the inversion layer is induced at the silicon surface. The increase in effective carrier lifetime may be due to slow recombination of excess minority carriers stored in the inversion layer at the SiO2/Si interface with a low interface trap density and/or slow diffusion of the excess minority carriers into the bulk of the silicon.

The effect of drift and diffusion of minority carriers into regions of high recombination which occur at the metal/semiconductor interface of contacts, has the effect of reducing the density of photogenerated excess carriers in photoconductive devices. This loss of photogenerated carriers, which is enhanced at higher applied electric fields, is known as minority carrier sweepout, and is an important mechanism that limits the performance of HgCdTe photoconductive devices operating at high bias fields. In this study, experimentally determined contact recombination velocities range from 25 cm/s at 80 K, to 600 cm/s at 200 K for x=0.31 Hg/sub 1-x/Cd/sub x/Te. Hence, it is concluded that contact recombination is a dominant mechanism at higher temperatures even though it may not be significant at 80 K.

This paper presents a new technique for the simple and rapid evaluation of the process and geometry parameter contributions to BJT mismatch. The pinched base sheet resistance variation, the geometric emitter size variation, and the ideal component of the emitter-base current variation can be uniquely determined from the I/sub c/, I/sub b/ and /spl beta/ mismatch variances in the ideal region. The variation in the nonideal component of the base current can be evaluated from the I/sub b/ and /spl beta/ mismatch in low level injection region. The variation in extrinsic resistance can be evaluated from the I/sub c/ and I/sub b/ mismatch in the high current region. The mismatch evaluation can be performed with as few as six measurements per device type per die site.

This paper presents the analytical approach to modelling of high injection effects in bipolar transistors. It has been shown that Kirk effect occurs due to drop of carrier velocity within the vanishing base-collector depletion region at high injection operation of BJT. It leads to the "inverter"-like behavior of carrier velocity dependence on voltage, extracted at the end of base quasi-neutral region for low level injection. An analytical expression is derived which enables the calculation of minimum carrier velocity in high injection regime, showing it's variation with N/sup -/ technological parameters.

In this paper the susceptibility of voltage regulator circuits to electromagnetic interference is analyzed by experimental measurements. This analysis highlights two different effects of EMI on this circuit, for different levels of the injected power: an offset in the regulated voltage for low-level injection and a complete circuit failure for high-level injection. Both these effects are essentially related to the nonlinear behavior of the operational amplifier included in the circuit, in particular, the offset in the regulated voltage can be ascribed to previously investigated nonlinear effects of RFI on operational amplifiers input terminals and/or power supply rails.

The dynamics of hot minority carriers in p‐GaAs is calculated for doping concentrations in the range of 1.5×1017 cm−3 to 1.5×1018 cm−3. It is shown that the electron‐hole interaction increases the rate of dissipation of the excess energy of the minority carriers in the early stages of the process. However, this channel for energy dissipation becomes weaker as the cooling of the minority carriers proceeds, an effect more noticeable in the case of high doping levels. When the electron‐hole interaction is disregarded, the dissipation rate is always smaller for low doping concentrations.

Knowledge of both carrier bulk lifetime τb and surface recombination velocity S are necessary to analyze and model electron devices. In this paper, the analytical results of Luke and Cheng [J. Appl. Phys. 61, 2282 (1987)] are applied to examine excess carrier decay due to pulsed Gaussian optical excitation to extract values of τb and S under low level injection. The nondestructive, contactless measurement technique utilizes a visible pulsed laser pump beam and a CW infrared laser probe beam. Values for τb and S are obtained for a number of different Si samples. The effect of varying the pump beam frequency is examined. The technique is simple to use in the laboratory and the parameter extraction from the measured data is straightforward.

The carrier recombination rate in GaAs‐AlGaAs single quantum well layers is investigated using a small‐signal technique for carrier densities from 1017 to 1019/cm3. For carrier densities up to mid 1018/cm3, the inverse of the differential carrier lifetime, 1/τd, increases linearly with the carrier density. The differential rate, however, saturates at higher carrier densities and remains nearly constant for carrier densities higher than 1019/cm3. The deviation from the bulk recombination behavior is due to a portion of the injected carriers populating the semicontinuum states where the rate for the radiative transition is much smaller. The experimental data indicate that the runaway increase of threshold current with decreasing cavity length commonly observed in the short‐cavity lasers is mainly due to the loss of carrier confinement at high carrier densities rather than due to fast carrier‐depleting processes, such as Auger recombination.

This paper presents an accurate and practical mathematical model of time-resolved photoluminescence (PL) response from silicon wafers generated by fast repetitive excitation pulses. The model is valid under low level injection condition and takes into account the depth dependence of carrier generation, diffusion, and surface recombination. Finite element analysis is employed for the carrier density and PL computations. By comparing computational results with results obtained from PC1D (a computer program solving fully coupled nonlinear equations for quasi-one-dimensional carrier transportation in crystalline semiconductor devices, especially focusing on photovoltaic devices), the validity of this method is confirmed. Early stage application and the limitations of this method have been studied, and future work has been proposed.

As was noted in the cover letter that accompanied the samples, the eleven bare silicon samples were from various manufacturers. Table I lists the codes for the samples and the manufacturer of each sample. It also notes if the sample was single or poly-crystalline. The samples had been polished on one side before being sent out for measurements, but no further processing was done. The participants of the study were asked to measure either the lifetime or diffusion length of each of the samples using their standard procedure. Table II shows the experimental conditions used by the groups who measured diffusion length. All the diffusion length measurements were performed using the Surface Photovoltage method (SPV). Table M shows the experimental conditions for the lifetime measurements. All the lifetime measurements were made using the Photoconductance Decay method (PCD) under low level injection. These tables show the diameter of the spot size used during the measurement (the effective sampling area), the locations where measurements were taken, and the number of measurements taken at each location. Table N shows the results of the measurements. The table is divided into diffusion length and lifetime measurements for each sample. The values listed are the averagemore » values reported by each group. One of the immediate artifacts seen in the data is the large variation in the lifetime measurements. The values from MIT and Mobil are generally close. However, the measurements from NCSU are typically an order of magnitude lower.« less

In this paper we show experimental results that indicate that trapping-related increase of the apparent carrier lifetime can be directly accompanied by a decreased recombination lifetime. This effect cannot be described with the traditionally used trapping model of Hornbeck and Haynes [1,2,3] (H&H). In order to obtain a physically consistent theoretical description of the observed correlation between trapping and recombination we use the Shockley, Read [4] and Hall [5] (SRH) formalism. We assume trap states with non-zero capture cross sections for majority carriers, which may nevertheless be several orders of magnitude smaller than the minority carrier capture cross sections. In this way we define a Recombination-Active Trap state (RAT) that allows a simultaneous description of trapping effects and a reduction of the recombination lifetime in low level injection.

Fluorescence Studies of Surface Recombinationin CdSe ElectrodesM.L. Shumaker, D. Burdeiski and D.H. WaldeckDepartment of Chemistry,University of Pittsburgh,Pittsburgh, PA 15260ABSTRACTFluorescence decay profiles are used to monitor carrier dynamics at theinterface between single crystalline CdSe electrodes and 0.5M KOH solution. Thefluorescence decay profiles are found to be independent of temperature over therange from 277K to 337K. It is also shown that a diffusion model of the carrierdynamics with a single rate constant for surface recombination does notadequately describe the observed dynamics.1. INTRODUCTIONWith extrinsic material under low level injection conditions and when selfabsorption is small the fluorescence decay provides a temporal profile of theminority carrier concentration. The fluorescence decay can be exploited tomonitor the dynamics of charge carrier relaxation and charge transfer at thesemiconductor/electrolyte interface. Time-resolved bandgap fluorescence hasbeen used to determine the surface recombination velocity of photogeneratedcarriers in semiconductor electrodes. Fluorescence studies of Il—VI compounds,in particular CdSe and CdS, in contact with electrolyte solutions is available[1,2]. The earlier work concentrates on the influence of surface preparationand electrolyte composition on the surface recombination velocity. In general,agreement with simple diffusion models of carrier motion has been observed, orassumed. The electrolyte composition, as well as surface preparation, is foundto strongly affect the recombination velocity. An asset of time-resolvedstudies is the ability to directly test the validity of diffusion models for thecarrier motion and recombination.The work reported here on the fluoresence decay of CdSe electrodes istwofold. First decay profiles are shown which are not adequately described by asimple diffusion model for the carrier dynamics. Second a temperature study ofthe carrier recombination reveals that the surface recombination velocity doesnot have a strong temperature dependence.2. MODEL OF CARRIER DYNAMICSAn appropriate model for the carrier motion probed by thesestudies is diffusion of minority carriers,6p(r,t) =

A unified delay model is presented that predicts BiCMOS gate delay for both long- and short-channel MOSFETs, in low-level and high-level injection in the bipolar junction transistors (BJTs), for 5 V and reduced supply and over a wide range of circuit parameter variation. The model is applied to devise circuit and device design strategies to optimize gate performance at 5 V and at scaled supply voltage. The model predicts analytical expressions for an optimum BJT emitter length versus MOS gate width for which the delay is a minimum. To minimize performance degradation at reduced supply, an effective circuit strategy is to design with wide MOS devices and small-length BJTs. The crucial BJT parameters are (reduced) junction capacitance, (reduced) transit time and the gain-knee current product. For the MOSFET the saturation current must be maximized and gate length scaling is desirable as long as the saturation current increases

We present spatially resolved and injection dependent excess carrier lifetime measurements on silicon. At low level injection conditions an anomalous increase often interferes in such measurements. The origin of the anomalous increase is discussed. Assuming trapping as the origin, highly resolved images of trap parameters together with low level injection recombination lifetimes with strongly reduced trapping effects have been obtained. A theoretical model for infrared lifetime imaging based on the Hornbeck and Haynes model [J. A. Hornbeck and J. R. Haynes, Phys. Rev. 97, 311 (1955)] is presented which describes the trapping effect on the measured lifetime. This model is fitted to experimental spatially resolved data to extract trapping parameters, particularly trap density and the trap-escape ratio, i.e., the ratio between escape rate of minority carriers from the trap level into the minority band (detrapping) and trap rate from the minority band into the trap level (trapping). An upper bound for the low level injection recombination lifetimes is determined. Lifetime and trapping parameters are compared with dislocation density maps. A strong correlation is found between the total trap density and the crystal defect density.

The present investigation deals with the distributed parameter analysis of the p–n junction solar cell in the current-induced case at low level injection. The theory, for the first time, takes into account the metal–semiconductor contact resistance, along with the base bulk resistance and the diffused layer shear resistance. The transcendentally nonlinear differential equations for the emitter layer current and voltage have been solved analytically. Additionally, expressions for the I–V characteristic and equivalent ‘lumped’ series resistance have been established. Such physical parameters are very useful in the optimisation of the contact finger width and separation. Inclusion of the contact resistance, even for very small values, corresponds to the nonuniform carrier generation within the metallic grid. Therefore, the results are affected both qualitatively and quantitatively. The most important effect has been calculated in the I–V characteristics resulting from an additional contribution to the series resistance. Analysis reveals that the series resistance and the diode quality factor vary with applied current.

The reverse recovery time is calculated using a general expression for the net recombination rate through a recombination center. When the capture rate of minority carriers is high compared to that of majority carriers, the recovery time increases with the injection level even if the condition of low injection level is satisfied. This means that the apparent lifetime obtained from Kingston's relationship is larger than the true value. An approximate equation which relates the recovery time to the injection level is proposed.

The analysis of the response of a photoelectrochemical system to a variable light source offers a convenient means for the characterization of a semiconductor-electrolyte interface. The authors present analytic solutions for the minority carrier concentrations at the semiconductor surface during pulse, step, sinusoidal, and periodic-square-pulse illumination. The analytic solutions can be used to describe the low level injection behavior of wide bandgap semiconductors employed in photoelectrolysis cells and other photoelectrochemical systems.