Change In Carrier Lifetime Research Articles

Reassessing iron–gallium recombination activity in silicon

In this work, we present a comprehensive re-evaluation of the iron–gallium (FeGa) recombination parameters in silicon using injection-dependent lifetime spectroscopy (IDLS). Ga-doped silicon wafers (of varying resistivities) with precise concentrations of intentional iron contamination in the silicon wafer bulk, through ion implantation and distribution, were used. The presence of interstitial Fei and FeGa, and their lifetime-limiting effects in these silicon wafers, were confirmed through measuring the effective minority carrier lifetime changes during the conditions that are known to cause FeGa dissociation and association. The presence of Fe was also confirmed by deep-level transient spectroscopy. To ensure accurate IDLS analysis of the FeGa defect in silicon, a lifetime linearization scheme was employed to effectively filter out interference by other defects. Error analysis was employed to find the combination of defect parameters that best fit the experimental data and to ascertain the range of uncertainty associated with the IDLS best-fit results. The optimal fitting of the experimental IDLS by Shockley–Read–Hall statistics produced an electron capture cross section σn=2.3×10−14cm2, hole capture cross section σp=1.1×10−14cm2, and a trap energy level Et=EV+0.2−0.01+0.02eV for the FeGa defect in silicon. The extracted defect parameters are also verified by experimentally measuring the crossover point of Fei and FeGa lifetime curves.

Temperature dependent behavior of sub-monolayer quantum dot based solar cell

This work investigates the temperature dependence of the performance of In(Ga)As-based solar cells made from sub-monolayer (SML) quantum dots (QDs), quantum wells (QWs), and Stranski-Krastanov QDs (SK-QDs). Well-defined sub-bandgap peaks are observed in external quantum efficiency (EQE) spectra for all samples. Apparently, changes in minority carrier lifetime affect both the sub-bandgap and the above bandgap EQE. Lateral confinement of carriers in the SMLs and QDs also affects the temperature dependence of the EQE. Finally, a “U” shaped curve was observed from the temperature dependence of the short-circuit current (ISC) from these nanostructure-based solar cells. This is due to the competition between the decreasing bandgap and the increasing carrier loss to recombination within the nanostructures as the temperature increases. In contrast, the solar cell's open-circuit voltage and power efficiency decrease monotonically with temperature.

Understanding the Origin of Light Intensity and Temperature Dependence of Photodetection Properties in a MAPbBr3 Single-Crystal-Based Photoconductor

Methylammonium lead bromide (MAPbBr3), which belongs to the larger material family of lead halide perovskites (LHPs), has emerged as a promising semiconductor for the fabrication of single-crystal (SC)-based photodetectors (PDs). However, there is still a lack of sufficient understanding of the effect of irradiation power and applied temperature on the photodetection performance of SC-based perovskite PDs. Here, we investigate the impact of different light intensities and temperatures on the photodetection properties of planar-type MAPbBr3 SC-based PD with the help of transient photoresponse and impedance spectroscopy. The light intensity-dependent study revealed that the key performance parameters of PD decrease with increasing irradiation intensity due to changes in charge recombination and carrier lifetime. On the other hand, the detrimental effect of increasing temperature on the performance of PD was found to be related to the ion accumulation, increasing scattering of impurities and phonons, and change in conductivity and band gap rather than the change in charge recombination. This study provides a thorough understanding of the origin of light intensity and temperature-dependent photodetection properties of SC-based PD, which is crucial for the further advancement of optoelectronic devices based on LHPs.

Carrier lifetimes in gold–hyperdoped silicon—Influence of dopant incorporation methods and concentration profiles

Incorporating ultrahigh concentrations of deep-level dopants in silicon drastically alters silicon’s optoelectronic properties. Photodiodes built from silicon hyperdoped with gold extend light sensitivity into the shortwave infrared region, far beyond the absorption edge of a pristine silicon sample. Deep-level dopants, however, also enhance carrier recombination; even though hyperdoped silicon has great light absorption properties, short charge carrier lifetime limits its applications. In this work, using terahertz spectroscopy, we investigate the charge carrier lifetime of gold–hyperdoped silicon, where the gold dopants are introduced by either film deposition or ion implantation, followed by pulsed laser melting. Using reactive ion etching, we measure how carrier lifetime changes when dopant concentration profiles are altered. Furthermore, using a 1D diffusion and recombination model, we simulate carrier dynamics when electrons are excited by sub-bandgap light. Our results show that the dopant distribution profile heavily influences excited carrier dynamics. We found that etching improves the half-life by a factor of two. In the short-wave-infrared range, the gold dopants are both light absorption centers and recombination centers. Focusing on optoelectronic properties in the short-wave-infrared region, our results suggest that these samples are over doped—etching much of the gold dopants away has little impact on the number of excited electrons at a later time. Our results suggest that dopant profile engineering is important for building efficient optoelectronic devices using hyperdoped semiconductors.

Profiling of proton beams by fluence scanners

Profiling of particle beams is one of the most important diagnostic procedures for operating any kind of accelerator. In this work, the proton beam profilers, based on fluence measurements performed by recording the changes of carrier lifetime in Si material and scintillation intensity of thin GaN layers, caused by radiation induced defects and emission centres, are presented. The beams of penetrative (26 GeV/c) and stopped (1.6 MeV) protons have been examined. It is shown that the penetrative particle regime should be employed to appropriately record 2D fluence distribution profiles. It is also illustrated that the presented profiling techniques can be applied for scanning of other charged (namely, pions) and neutral (neutrons) particle beams.

Study of degradation in 3J inverted metamorphic (IMM) solar cell due to irradiation-induced deep level traps and threading dislocations using finite element analysis

Abstract This paper emphasizes on III-V material based inverted metamorphic triple junction (3J IMM) solar cell as an alter-native to 3J lattice-matched InGaP/GaAs/Ge design (3J LM). 1-sun AM0 efficiency is obtained to be 7% higher for the proposed 3J IMM InGaP/GaAs/In0.30Ga0.70As design compared to the experimental 3J LM solar cell. The mi- nority carrier lifetime as a function of threading dislocation density (TDD) is presented for p-In0.30Ga0.70As material. The influence of TDD in the buffer and the bottom In0.30Ga0.70As subcell on the device characteristics is presented and analyzed. In addition to TDD, the degradation of solar cell output parameters is plotted as a function of trap concentration by considering irradiation-induced deep level traps. We compared the degradation tendencies of short circuit current density Jsc, open circuit voltage Voc, and efficiency of 3J IMM and 3J LM solar cells with respect to trap concentration. This analysis became possible by defining trap related parameters and the corresponding carrier lifetime changes using the crosslight APSYS tool. In addition to superior radiation resistance, the proposed device has shown 4% higher efficiency compared to 3J LM device even with the inclusion of non-idealities such as surface recombination velocity, TDD, and trap concentration.

Correlation between OCVD carrier lifetime vs temperature measurements and reverse recovery behavior of the body diode of SiC power MOSFETs

The reverse recovery (RR) behavior of SiC MOSFET body diode is of great importance in power application, where these devices are used in a wide range of operating temperatures. The carrier lifetime in the drift region varies with temperature, and it heavily affects the tailoring of the RR current, opening reliability issues related to the RR voltage amplitude and to possible anomalous voltage oscillations during the recovery. From the users' point of view, it would be useful to have a simple technique able to give predictive information about the body diode RR behavior of commercial devices over the whole range of working temperatures. An experimental-simulation approach is presented in this paper to correlate the carrier lifetime measured by simple OCVD measurements versus temperature with the RR behavior of the body diode, that can be useful at the design stage of power converters. Simulations of the body diode reverse-recovery are performed for a wide range of carrier lifetimes. This allows to estimate the effect of changes of carrier lifetime with temperature on the body diode switching transients. Preliminary results obtained with a 1700 V/5A commercial MOSFET are shown.

Direct-indirect GeSn band structure formation by laser Radiation: The enhancement of Sn solubility in Ge

Low equilibrium solid solubility of Sn atoms in Ge (less than 1%) leads to limitations in application of this material for IR detectors and emitters. Providing of non-equilibrium conditions by powerful pulsed laser radiation can be successfully applied for enhancement of solubility of impurity atoms in the host material. Here we present laser-induced monotonous redistribution of Sn atoms in Ge, based on the thermogradient effect aiming overcoming equilibrium limitations in the solubility. We applied pulsed nanosecond laser radiation to epitaxial Ge0.96Sn0.04 layer grown on Si substrate to increase Sn atomic concentration up to 14% at the surface layer. As a result, indirect-direct graded bandgap GeSn structure was formed. The TEM/EDS cross-section analysis, X-ray photoelectron spectroscopy, Raman and UV reflection spectra confirmed the increase of Sn atomic content at the surface by order of magnitude. SEM and AFM imaging provided evident microstructure changes, while carrier lifetime changes, determined by differential transmittivity, were not observed, indicating that laser irradiation does not generate defects which reduce electronic quality of the material.

On the Lifetime-Equivalent Defect Density: Properties, Application, and Pitfalls

The basic idea, derivation, and definition of the lifetime-equivalent defect density (alternatively termed as effective, relative, or normalized defect density) in the context of studies on changes of bulk excess charge carrier lifetime in crystalline silicon is presented, and the general dependencies on injection and temperature are discussed. As the concept of lifetime-equivalent defect density is often applied to light-induced phenomena, the application to boron–oxygen-related light-induced degradation and regeneration is demonstrated by means of simulations, as well as the pitfalls, when other phenomena like iron–boron pairing/dissociation, light- and elevated-temperature-induced degradation and regeneration, or surface-related degradation are superimposed. Finally, the concept of lifetime-equivalent defect density is extended to surface phenomena.

The coupling effects of the different carrier generation rate distributions and recombination caused by nanostructures on the all-back-contact ultra-thin silicon solar cell performances

Ultra-thin silicon solar cell is a kind of good cost-effective energy solution. Moreover, nanostructured front surface and all-back contact design have been proposed as the promising methods to make ultra-thin silicon an effective solar irradiance absorber. Different nanostructures result in the different generation rate distributions and surface recombination, even though their corresponding integrated generation rates are the same. In addition, under the effect of carrier lifetime, the different generation rate distributions determine the number of carriers that reach the electrodes. Therefore, the grating nanostructures with three different section shapes are chosen for the investigation of the coupling effects of the different generation rate distributions and recombination caused by nanostructures. After consideration of the effect of the surface enhancement ratio of nanostructure, the deviation of electrical characteristics (fill factor), which is caused by the different generation rate distributions caused by nanostructures with the same integrated generation rate, is 0.20% at most as the effective surface recombination increases. Meanwhile, as the carrier lifetime decreases, the deviation of electrical characteristics (short circuit current) is only 1.80% at maximum and does not change with carrier lifetime. Therefore, it is found that, in all-back-contact ultra-thin silicon solar cell, the different generation rate distributions caused by nanostructures with the same integrated generation rate have little effect on the electrical characteristics, no matter how the effective surface recombination and carrier lifetime change. Based on the conclusion, a simplified method is developed for the electrical characteristics simulations. As the effective surface recombination and carrier lifetime change, the minimum error of electrical characteristics calculated by the simplified method is 0.06%, and the maximum is just 3.10%, which proves its accuracy.

High Responsivity Ultraviolet Photoconductors Based on Epitaxial ZnO Thin Films

In this paper, ultraviolet (UV) detection properties of epitaxial ZnO films grown on sapphire substrates with radio-frequency magnetron sputtering is reported. The responsivity (R) of the ZnO photoconductors measured at 325 nm wavelength shows a strong dependence on the incident power (P), i.e., R µ P-k (k = 0.7). A responsivity of 3500 A/W (or a gain of 6000) is obtained at the optical power density of 10-7 W/cm2, and the value decreases to 1 A/W at 10-2 W/cm2. The ultra-high responsivity at the low power regime suggests a long lifetime (order of 10 ms) of carriers. The enhanced carrier lifetime is explained by the preferential capture of holes at the recombination centers that exist in the depletion region around grain boundaries and film surface, and the subsequent separation of photogenerated carriers. The strong dependence of the responsivity on the incident power is attributed to the modulation of space charge region width by the photogenerated holes and the resulting change in carrier lifetime.

Acousto–defect interaction in irradiated and non-irradiated silicon n+–p structures

The influence of ultrasound on current–voltage characteristics of non-irradiated silicon n+–p structures as well as silicon structures exposed to reactor neutrons or 60Co gamma radiation has been investigated experimentally. It has been found that the ultrasound loading of the n+–p structure leads to the reversible change of shunt resistance, carrier lifetime, and ideality factor. Specifically, considerable acoustically induced alteration of the ideality factor and the space charge region lifetime was observed in the irradiated samples. The experimental results were described by using the models of coupled defect level recombination, Shockley–Read–Hall recombination, and dislocation-induced impedance. The experimentally observed phenomena are associated with the increase in the distance between coupled defects as well as the extension of the carrier capture coefficient of complex point defects and dislocations. It has been shown that divacancies and vacancy–interstitial oxygen pairs are effectively modifi...

Study of neutron irradiated structures of ammonothermal GaN

Study of the radiation damage in GaN-based materials becomes an important aspect for possible application of the GaN detectors in the harsh radiation environment at the Large Hadron Collider and at other particle acceleration facilities. Intentionally doped and semi-insulating bulk ammonothermal GaN materials were studied to reveal the dominant defects introduced by reactor neutron irradiations. These radiation defects have been identified by combining electron spin resonance and transmission spectroscopy techniques. Characteristics of carrier lifetime dependence on neutron irradiation fluence were examined. Variations of the response of the capacitor-type sensors with neutron irradiation fluence have been correlated with the carrier lifetime changes. The measurements of the photoconductivity and photoluminescence transients have been used to study the variation of the parameters of radiative and non-radiative recombination. The examined characteristics indicate that AT GaN as a particle sensing material is radiation hard up to high hadron fluences ⩾1016 cm−2.

Pseudodirect to Direct Compositional Crossover in Wurtzite GaP/InxGa1-xP Core-Shell Nanowires.

Thanks to their uniqueness, nanowires allow the realization of novel semiconductor crystal structures with yet unexplored properties, which can be key to overcome current technological limits. Here we develop the growth of wurtzite GaP/InxGa1-xP core-shell nanowires with tunable indium concentration and optical emission in the visible region from 590 nm (2.1 eV) to 760 nm (1.6 eV). We demonstrate a pseudodirect (Γ8c-Γ9v) to direct (Γ7c-Γ9v) transition crossover through experimental and theoretical approach. Time resolved and temperature dependent photoluminescence measurements were used, which led to the observation of a steep change in carrier lifetime and temperature dependence by respectively one and 3 orders of magnitude in the range 0.28 ± 0.04 ≤ x ≤ 0.41 ± 0.04. Our work reveals the electronic properties of wurtzite InxGa1-xP.

A Model of Radiative Recombination in (In,Al,Ga)N/GaN Structures with Significant Potential Fluctuations

The potential fluctuations in III-nitride quantum wells lead to many effects like emission broadening and S-shape energy vs. temperature dependence. The best description of the energy dependence comes from calculations based on Gaussian density of states. However, in most of the published reports, changes of carrier lifetime with energy and temperature are not taken into account. Since experimental evidence shows that lifetime significantly depends on energy and temperature, here we propose a model that describes two basic parameters of luminescence: lifetime of carries and emission energy as a function of temperature in the case of quantum wells and layers that are characterized by potential fluctuations. Comparison of the measured energy and lifetime dependences on temperature in specially grown InGaN/GaN quantum wells and InAlGaN layer shows very good agreement with the proposed theoretical approach.

Temperature dependency of the silicon heterojunction lifetime model based on the amphoteric nature of dangling bonds

This work adapts a model to simulate the carrier injection dependent minority carrier lifetime of crystalline silicon passivated with hydrogenated amorphous silicon at elevated temperatures. Two existing models that respectively calculate the bulk lifetime and surface recombination velocity are used and the full temperature dependency of these models are explored. After a thorough description of these temperature dependencies, experimental results using this model show that the minority carrier lifetime changes upon annealing of silicon heterojunction structures are not universal. Furthermore, comparisons of the temperature dependent model to using the room temperature model at elevated temperatures is given and significant differences are observed when using temperatures above 100 °C. This shows the necessity of taking temperature effects into account during in-situ annealing experiments.

The Effect of Phosphorus Diffusion Gettering on Recombination at Grain Boundaries in HPMC-Silicon Wafers

The influence of phosphorus diffusion gettering on recombination at grain boundaries has been studied in a commercially cast high performance multicrystalline silicon block. Wafers from four different heights have been studied with high resolution photoluminescence-imaging. The recombination at grain boundaries was studied from linescans perpendicular to the grain bounadary of interest. The change in recombination activity at grain boundaries after gettering has been correlated with grain orientation measured by electron backscatter diffraction and classified according to Brandon criterion. The relative change in carrier lifetime after gettering depends on the height in the cast, and is very sensitive to the injection level. Iron concentrations were also found from photoluminescence-imaging of iron in Fei and FeB states, respectively. After gettering recombination grain boundaries in the middle section of the ingot has become strongly recombination active. Fei, has been efficiently removed and no longer constitute the main recombination path at any height.

Comparison of phosphorus gettering effect in faceted dendrite and small grain of multicrystalline silicon wafers grown by floating cast method

We attempt to clarify the effect of phosphorus diffusion gettering (PDG) on the differences in microstructures of multicrystalline silicon (mc-Si) wafers. From the results of the floating cast method, the obtained microstructure of mc-Si was determined to contain unique microstructures, consisting of large faceted dendrites and small grains with low and high dislocation densities. The PDG efficiency was evaluated through the change in minority carrier lifetime. As a result, a stronger positive PDG effect was found for large faceted dendrites with low dislocation density, attributed to a small number of defects that can act as recombination centers of carriers. Lifetime improvement was also found in dislocation regions possibly owing to the redistribution of interstitial metals. These results suggest the importance of controlling the microstructure of mc-Si, which could strongly affect the PDG efficiency and existence of incorporated impurities.

Band offsets of n-type electron-selective contacts on cuprous oxide (Cu2O) for photovoltaics

The development of cuprous oxide (Cu2O) photovoltaics (PVs) is limited by low device open-circuit voltages. A strong contributing factor to this underperformance is the conduction-band offset between Cu2O and its n-type heterojunction partner or electron-selective contact. In the present work, a broad range of possible n-type materials is surveyed, including ZnO, ZnS, Zn(O,S), (Mg,Zn)O, TiO2, CdS, and Ga2O3. Band offsets are determined through X-ray photoelectron spectroscopy and optical bandgap measurements. A majority of these materials is identified as having a negative conduction-band offset with respect to Cu2O; the detrimental impact of this on open-circuit voltage (VOC) is evaluated through 1-D device simulation. These results suggest that doping density of the n-type material is important as well, and that a poorly optimized heterojunction can easily mask changes in bulk minority carrier lifetime. Promising heterojunction candidates identified here include Zn(O,S) with [S]/[Zn] ratios >70%, and Ga2O3, which both demonstrate slightly positive conduction-band offsets and high VOC potential. This experimental protocol and modeling may be generalized to evaluate the efficiency potential of candidate heterojunction partners for other PV absorbers, and the materials identified herein may be promising for other absorbers with low electron affinities.

Lateral scan profiles of the recombination parameters correlated with distribution of grown-in impurities in HPHT diamond

Abstract The profiling of the microwave probed photoconductivity transients and of the time resolved photoluminescence spectra has simultaneously been performed on the synthetic diamond wafer samples in order to clarify correlation of the distribution of the grown-in defects and carrier radiative and non-radiative recombination channels. The wafer samples were sliced from the diamond single crystals, synthesized by the high pressure and high temperature (HPHT) technology using the Ni–Fe liquid solvent/catalyst system. To estimate the microscopic characteristics of the grown-in defects, the EPR spectroscopy has been carried out. The changes of carrier lifetime, ascribed to the radiative and non-radiative recombination, have been resolved. The correlation between the parameters extracted from the absorption spectra and recombination characteristics has been obtained. The prevailing grown-in point defects, associated with neutral and charged nitrogen impurity complexes as well as the pairs of nitrogen atoms on neighbouring sites, and the nickel precipitates have been unveiled.