Dependence Of Carrier Lifetime Research Articles

Understanding the Strong Apparent Injection Dependence of Carrier Lifetimes in Doped Polycrystalline Silicon Passivated Wafers

This study investigates the injection dependence of carrier lifetimes of p‐ and n‐type samples passivated by doped‐polycrystalline silicon (poly‐Si) (p+ and n+ poly‐Si) contacts. A strong apparent injection dependence of the carrier lifetimes is observed in p‐n junction samples (p+ poly‐Si on n‐type or n+ poly‐Si on p‐type) but no injection dependence is observed in high‐low junction samples (p+ poly‐Si on p‐type or n+ poly‐Si on n‐type). Further, photoluminescence images captured at two illumination intensities of 0.05 and 0.87 suns reveal that edge recombination contributed the strong apparent injection dependence in p‐n junction samples. Furthermore, this apparent injection dependence increases as the sample size is reduced, and as the sheet resistance of the doped poly‐Si contacts is decreased, allowing more effective transport of minority carriers to the recombination‐active edge regions.

Carrier lifetime dependence on temperature and proton irradiation in 4H-SiC device: an experimental law

Carrier lifetime dependence on temperature and proton irradiation in 4H-SiC device: an experimental law

Nonlinear Inertial Diode Model Considering the Dependence of Nonequilibrium Charge Carrier Lifetime on Direct Current to Improve Simulation of Radioelectronic Equipment

Introduction. Adequate modeling of semiconductor devices with a p–n-junction in reverse bias represents a relevant research problem. The existing quasistatic and non-quasistatic models fail to provide a satisfactory description for the dependence of nonequilibrium charge carrier lifetime on current density. This leads to significant simulation errors (tens of percent) at pulsed broadband signals. Simulation errors arise, because the existing models regard the lifetime as a constant value.Aim. To propose and investigate an equivalent circuit of a p–n-junction considering the dependence of the lifetime of nonequilibrium charge carriers on direct current, with the possibility of its simple integration into CAD.Materials and methods. The study was carried out on the example of a fast recovery silicon diode BAS16J with a p–n-junction manufactured by Nexperia. A modified diode model is proposed in the form of an equivalent circuit that considers the dependence of the lifetime of nonequilibrium charge carriers on the direct current of the p–njunction at high injection levels.Results. The discrepancy between the experimental and simulated curves did not exceed ±9 % under pulsed diode operation. The extraction of parameters in the proposed model is carried out conventionally, from the current-voltage and capacitance-voltage characteristics of the diode.Conclusion. The proposed non-quasistatic equivalent diode circuit can be used when designing radio electronic devices operated at short-pulse broadband signals. The proposed diode model can be easily implemented in modern CAD systems at the user level.

The Effect of Fractionation during the Vacuum Deposition of Stabilized Amorphous Selenium Alloy Photoconductors on the Overall Charge Collection Efficiency.

The general fabrication process for stabilized amorphous selenium (a-Se) detectors is vacuum deposition. The evaporant alloy is typically selenium alloyed with 0.3–0.5%As to stabilize it against crystallization. During the evaporation, fractionation leads to the formation of a deposited film that is rich in As near the surface and rich in Se near the substrate. The As content is invariably not uniform across the film thickness. This paper examines the effect of non-uniform As content on the charge collection efficiency (CE). The model for the actual CE calculation is based on the generalized CE equation under small signals; it involves the integration of the reciprocal range-field product (the schubweg) and the photogeneration profile. The data for the model input were extracted from the literature on the dependence of charge carrier drift mobilities and lifetimes on the As content in a-Se1−xAsx alloys to generate the spatial variation of hole and electron ranges across the photoconductor film. This range variation is then used to calculate the actual CE in the integral equation as a function of the applied field. The carrier ranges corresponding to the average composition in the film are also used in the standard CE equation under uniform ranges to examine whether one can simply use the average As content to calculate the CE. The standard equation is also used with ranges from the spatial average and average inverse. Errors are then compared and quantified from the use of various averages. The particular choice for averaging depends on the polarity of the radiation-receiving electrode and the spatial variation of the carrier ranges.

Study of nonlinear effects and self-heating in a silicon microring resonator including a Shockley-Read-Hall model for carrier recombination.

A detailed description of the non-linear effects in silicon is needed when designing ring resonators in the silicon platform. The optical field propagating in the ring waveguide is strongly absorbed due to two-photon-absorption (TPA) and free-carrier-absorption (FCA), which become more prominent with increasing the input power in the ring. We present a new approach for the modelling of non-linear effects in silicon based ring resonators. We have numerically solved the non-linear problem coupling the variation of refractive index and loss due to TPA, FCA , self-heating and Shockley-Read-Hall (SRH) theory for trap-assisted recombination process. The model is validated by reproducing experimental measurements on a ring and a racetrack resonator having different Q-factors and waveguide cross-sections. As a result, we show that the SRH recombination is the origin of the dependence of free carrier lifetime on the power circulating in the ring and how this dependence is affected by the surface trap density and trap energy level. The model is then applied to the calculation of the maximum power that can incident the silicon rings designed for the Si PIC mirror of a hybrid III-V/Si widely tunable laser.

Studying the lifetime of charge and heat carriers due to intrinsic scattering mechanisms in FeVSb half-Heusler thermoelectric

This work, presents a study of lifetime of carriers due to intrinsic scattering mechanisms viz. electron–electron interaction (EEI), electron–phonon interaction (EPI) and phonon–phonon interaction (PPI) in a promising half-Heusler thermoelectric FeVSb. Using the full-GW method, the effect of EEI and temperature on the valence and conduction band extrema and band gap are studied. The lifetime of carriers with temperature are estimated at these band extrema. At 300 K, estimated value of lifetime at VBM (CBM) is ∼1.91 × 10−14 s (∼2.05 × 10−14 s). The estimated ground state band gap considering EEI is ∼378 meV. Next, the effect of EPI on the lifetime of electrons and phonons with temperature are discussed. The comparison of two electron lifetimes suggests that EEI should be considered in transport calculations along with EPI. The average acoustic, optical and overall phonon lifetimes due to EPI are studied with temperature. Further, the effect of PPI is studied by computing average phonon lifetime for acoustic and optical phonon branches. The lifetime of the acoustic phonons are higher compared to optical phonons which indicates acoustic phonons contribute more to lattice thermal conductivity (κ ph). The comparison of phonon lifetime due to EPI and PPI suggests that, above 500 K EPI is the dominant phonon scattering mechanism and cannot be ignored in κ ph calculations. Lastly, a prediction of the power factor and figure of merit of n-type and p-type FeVSb is made by considering the temperature dependent carrier lifetime for the electronic transport terms. This study shows the importance of considering EEI in electronic transport calculations and EPI in phonon transport calculations in FeVSb. Our study is expected to provide results to further explore the thermoelectric transport in this material.

Temperature and spatial dependence of carrier lifetime and luminescence intensity in Ge0.95Sn0.05 layer

In this work we present a study of spatial and temperature dependencies of carrier lifetime and photoluminescence in pseudomorphic Ge0.95Sn0.05 layer on silicon by applying contactless time-resolved differential absorption and photoluminescence techniques. The observed small lifetime and photoluminescence intensity spatial variations (~10%) indicate for good material homogeneity. Differential transmission kinetics exhibit fast bleaching and slow absorption components related to thermalization (few hundreds of picoseconds) and surface recombination (few tens of nanoseconds) processes. Temperature dependent photo-luminescence measurements indicate activation of carriers from L to Γ valley, governing dominant direct photoluminescence emission band at 1850 nm at 300 K. These direct transitions explain more efficient and blue-shifted by 150 nm photoluminescence emission at room temperature. At low temperatures direct emission is related to non-thermalized carriers, while indirect one is caused by depopulation of light hole band with temperature.

Temperature dependent carrier lifetime, diffusion coefficient, and diffusion length in Ge0.95Sn0.05 epilayer

The development of new technology, which would be able to shift photosensitivity of Si devices to the mid-infrared range, preserving the benefits of cheap silicon readout circuits, is of high priority for short-wave infrared photo-detection in defense, medical, night vision, and material production applications. Group IV GeSn-based materials have recently shown promising optoelectronic characteristics, allowing extension of the detection range to the mid-infrared region. However, the electronic properties of the material are not well understood and need further research. In this work, we provide temperature dependent studies of carrier lifetime, diffusion coefficient, and diffusion length in Ge0.95Sn0.05 epilayer on silicon by applying contactless light induced transient grating technique. The observed temperature dependence of lifetime was explained by the recombination of carriers on vacancy-related defects. The electron and hole capture cross sections were calculated. The temperature dependence of the diffusion coefficient indicated hole mobility limited by phonon and defect scattering. Weakly temperature dependent diffusion length of ∼0.5 μm verified material suitability for efficient submicrometer-thick optoelectronic devices.

Charge Carrier Recombination Dynamics of Two-Dimensional Lead Halide Perovskites.

Two-dimensional (2D) lead halide perovskites with better chemical stability and tunable dimensionality offer new opportunities to design optoelectronic devices. We have probed the transient absorption behavior of 2D lead halide (bromide and iodide) perovskites of different dimensionality, prepared by varying the ratio of methylammonium:phenylethylammonium cation. With decreasing dimensionality (n = ∞ → 1), we observe a blue shift in transient absorption bleach in agreement with the trend observed with the shift in the excitonic peak. The lifetime of the charge carriers decreased with decreasing layer thickness. The dependence of charge carrier lifetime on the 2D layers as well as the halide ion composition shows the dominance of excitonic binding energy on the charge carrier recombination in 2D perovskites. The excited-state behavior of 2D perovskites discussed in this study shows the need to modulate the layer dimensionality to obtain desired optoelectronic properties.

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.

Photo-excited carrier relaxation dynamics in two-dimensional InSe flakes

Carrier relaxation dynamics of InSe flakes is investigated by using time-resolved pump-probe reflectivity measurement. The photocarriers associated with the Pxy orbital band-edge transition at 2.40 eV, which is coupled to the in-plane polarized light, is observed to possess a lifetime of ∼19 ps at room temperature and ∼99 ps at 10 K. The temperature and power dependent carrier lifetime suggests that Shockley–Read–Hall process is the dominant nonradiative recombination mechanism responsible for the carrier relaxation. In addition, the electron scattering with a 14.5 meV optical phonon plays an active role in the carrier relaxation with increasing temperatures. A broad absorption around 1.65–1.90 eV is observed. The photocarriers associated with this broad transition show a long lifetime of ∼200 ps that is nearly independent of temperature and photon energy. This is indicative of bound carriers by defects. Our experimental results provide essential information for the characteristics of carrier dynamics and defects in InSe flakes. The experimental findings are fundamentally important for further development of microelectronics and optoelectronics based on InSe.

Anharmonicity Extends Carrier Lifetimes in Lead Halide Perovskites at Elevated Temperatures.

Lead halide perovskites constitute a very promising class of materials for a broad range of solar and optoelectronic applications. Perovskites exhibit many unusual properties, and recent experiments demonstrate an unusual temperature dependence of charge carrier lifetimes. Focusing on the all-inorganic CsPbBr3, and using a combination of ab initio nonadiabatic molecular dynamics and time-domain density functional theory, we demonstrate that the unconventional behavior arises because of a highly anharmonic nature of atomic motions in perovskites. As temperature increases, perovskite structure undergoes a notable deformation, reflected in tilting of octahedral units, and experiences large-scale anharmonic movements away from the equilibrium geometry. As a result, the electronic energy gap increases, and phonon-induced loss of coherence within the electronic subsystem accelerates. These two factors slow down nonradiative electron-hole recombination, which constitutes the main limitation on efficiencies of perovskite solar, optical, and electronic devices. The increase of charge carrier lifetimes with temperature is particularly beneficial in applications, because materials heat up, for instance, from sunlight during solar energy harvesting. The behavior of the all-inorganic halide perovskite investigated here is different from that of hybrid organic-inorganic perovskites, which exhibit additional disorder associated with reorientations of the asymmetric organic cations. The reported simulations generate an in-depth understanding of the unusual properties of inorganic perovskites, relevant for photocatalytic, photovoltaic, electronic, and optical applications.

Application of the Concept of Lifetime‐Equivalent Defect Density in Defect Systems Comprising a Multitude of Defect Species

The specific injection dependence of either excess carrier lifetime or lifetime‐equivalent defect density generally allows for the identification of a single defect species and the analysis of its properties. However, the presence of a multitude of defect species noticeably complicates this endeavor. A temporally different activation/deactivation dynamic of different defect species, as encountered in the context of light‐induced degradation phenomena in crystalline silicon solar cells, in combination with the distinct injection dependence of specific defect species can help to distinguish the involved defect species. Within this simulation‐based contribution, it is shown how injection‐dependent information can be used to reveal the presence of a second defect species in the context of light‐induced degradation and to distinguish clearly whether the formation of deep‐level defects in the bulk or a deterioration in the surface passivation quality is responsible for an observed degradation of effective excess carrier lifetime.

Time Dependence of Transient Radiative Excess Carrier Lifetimes and Carriers Density in Indium Antimonide(InSb) Semiconductor in the Presence and Absence of Illumination

In this work, we models the optical generation and transient radiative recombination excess carrier lifetimes in direct band gap semiconductors Indium antimonide (Insb) during illumination and after switching off the illumination. The time dependence of excess carrier density and excess carrier lifetimes are determined by using the doping level 1017cm-3 and absorption rate 1:21x1024cm-3s-1. The transient mean times for each excess carrier lifetimes to reach their steady-state values and excess carrier lifetime are determined.

Impact of intrinsic defects on excitation dependent carrier lifetime in thick 4H-SiC studied by complementing microwave photoconductivity, free-carrier absorption and time-resolved photoluminescence techniques

Photoexcited carrier dynamics in 1014–1018 cm−3 density range was investigated by using complementary optical and microwave techniques. Bulk lifetime decrease from 4 μs to 460 ns with excitation and its increase with temperature were observed in bulk n-type 4H-SiC crystal. The latter data and modeling of excitation-dependent hole capture with subsequent electron capture provided the trap position at EV + 0.19 eV and electron (hole) lifetimes of 360 ns (100 ns), correspondingly, at high excitation conditions. Lifetime increase with temperature was observed due to the trap thermal activation and reduction of electron capture cross section. The trap origin was discussed in terms of silicon vacancy related and titanium point defects. Photoluminescence spectra in 24–300 K range revealed bound exciton luminescence and nitrogen-aluminum donor-acceptor pair band, which time-resolved and excitation dependent dynamics was analyzed.

Pump dependent carrier lifetimes in InAs/GaAs quantum dot photoconductive terahertz antenna structures

In this paper, we study the behavior of photoexcited carriers in GaAs wafers containing self-assembled InAs quantum dots (QDs). These samples were designed and grown to be employed as photoconductive antennae for terahertz (THz) generation. The implanted QDs serve to shorten the overall carrier lifetime and enable pumping with lasers operating at wavelengths between 1μm and 1.3μm. Optical pump-THz probe measurements reveal carrier lifetime shortening for higher pump powers in the unbiased antennae due to increased carrier capture via Auger relaxation. This phenomenon significantly broadens the THz spectra from QD-based PCAs and explains the increased THz intensity at higher frequencies presented earlier.

High Thermoelectric Power Factor in IntermetallicCoSiArising from Energy Filtering of Electrons by Phonon Scattering

While highly conductive, intermetallic compounds are typically poor thermoelectrics, due to a small Seebeck coefficient. $B20$-type CoSi, however, exhibits an anomalously large, negative Seebeck coefficient. First-principles calculations reveal the underlying reason to be the strong energy dependence of carrier lifetimes due to phonon scattering, which leads to effective energy filtering of holes and low-energy electrons. The phenomenon originates from a band structure with both heavy and massless fermions near the Fermi level, and is thus intrinsic to the material. This insight opens an avenue for discovering and designing high-performance thermoelectrics for energy recovery.

Effect of the Near Surface Depletion Layer on Photo-Response of Direct Band Gap Semiconductor

In this study, the effects of the photo-responses of the near surface depletion layer and the deep bulk of gallium antimonide (GaSb) are investigated under different doping levels, injection level and illumination energies. First, the absorption rate of photons is described as a function of illumination energies at different locations inside the sample and as a function of the depth below the illuminated surface for photons with different energies. Then, the doping level dependence of the low injection level radiative, Auger and effective excess carrier lifetimes just under the surface and in the deep bulk are investigated by considering the variation of energy bending at the surface. The variation of the low injection level excess carrier lifetimes with the depth below the illuminated surface for samples with different doping levels is also described. This is followed by the description of the combined effects of doping and illumination energy on the photo-response of the entire bulk at slightly low injection level. Finally, the excess carrier injection level dependence of excess carrier lifetimes under the illuminated surface and deep bulk is also described for samples with different doping levels. Since photon absorption rate is directly related to the free carriers generation rate, the description of the photon absorption rate as functions of illumination energies and the depth below the illuminated surface is found to be the important and factors in the investigation in the photo-response of semiconductors along with the doping and the injection levels. The analysis of the results also shows that, the under surface region is insensitive to the doping level and that of the deep bulk is highly affected by the doping level. The injection level dependence of the photo-response of the under surface region is similar for all samples with different doping. The energy of illumination each photon mainly suppresses the photo-responses of the points situated closer to the penetration depths of each photon below the illuminated surface of the sample. Keywords: photo-response, direct band gap semiconductor, gallium antimonide GaSb DOI : 10.7176/APTA/75-03

Imaging Interstitial Iron Concentrations in Gallium‐Doped Silicon Wafers

In this work, the established method of iron imaging is transferred from B‐doped silicon to Ga‐doped material. For this purpose, the pairing and splitting conditions are investigated and a preparation procedure suggested that ensures a sufficient fraction of iron–gallium pairing and splitting, respectively. Furthermore the defect parameters available in literature are compared and evaluated for a suitable description of the injection dependent carrier lifetime measurements. A parameter set that enables a coherent and adequate iron evaluation is suggested. Thus, a robust method for spatially resolved determination of the interstitial iron concentration in Ga‐doped silicon wafers is presented.

Cascade capture of charge carriers in highly doped semiconductors

We analyze the cascade capture of charge carriers due to the interaction with acoustic phonons in highly doped semiconductors using a model that describes the recombination of photo-ionized carriers as a continuous relaxation of carriers in the energy space at both positive and negative energies in the field of a set of impurity ions. Such description enables simultaneous calculation of non-equilibrium carrier distribution formed by interaction with acoustic phonons in the presence of impurity traps, and the time of recombination in a wide range of concentrations of capture centers and phonon temperatures. Additionally, we calculated the time of cascade recombination in the presence of fast scattering processes forming a Maxwellian distribution of free carriers. We show that experimentally observed concentration and temperature dependence of carrier life times in highly doped semiconductors can be described within the model of the cascade capture to uniformly spaced capture centers, and the main factor that determines the regime of cascade capture is the ratio of the thermal energy and the energy of the overlap of impurity potentials.