Shockley Read Hall Recombination Research Articles

Device engineering of Sb2X3 antimony chalcogenide for loss analysis and strategies for maximizing photovoltaic efficiency

Antimony chalcogenide (Sb2X3; X=S, Se) is reportedly stable in ambient open-air, abundant, and shows composition-dependent absorption tunability. We simulated the Sb2X3 device utilizing the reported optical and electrical properties to analyze the performance limiting factors and the extent of achievable performance. Initially, we benchmarked the simulated device with the experimental reported device. The VOC-temperature and VOC-illumination characterization of the benchmarked device revealed the contact issue responsible for the VOC deficit. The suboptimal device configuration is a major performance-limiting factor. Contact optimization and conduction band offset optimisation have improved efficiency to 14.86% and 20.45% in Sb2S3 and Sb2Se3, from their experimentally reported values of 7.5% and 9.2% respectively. The optimization of trap-assisted Shockley Read Hall (SRH) recombination in bulk and interface has improved efficiency to 19.43% and 26.13% in Sb2S3 and Sb2Se3, respectively. When extrinsic factors are optimised, such as resistance losses (series resistance as high as 2 Ωcm2 and shunt resistance as low as 1000 Ωcm2), efficiency increased to 20.03% and 26.82% for Sb2S3 and Sb2Se3, respectively. Finally, with ideal intrinsic recombination parameters (radiative and Auger recombination), efficiency improved to theoretical limits (corresponding to their band gap). The study highlights the possibility of immediate gain upon contact passivation in Sb2S3 and Sb2Se3.

Sustained robust exciton emission in suspended monolayer WSe2 within the low carrier density regime for quantum emitter applications

The development of semiconductor optoelectronic devices is moving toward low power consumption and miniaturization, especially for high-efficiency quantum emitters. However, most of these quantum sources work at low carrier density regions, where the Shockley–Read–Hall (SRH) recombination may be dominant and seriously reduce the emission efficiency. In order to reduce the effect of carrier trapping and sustain a strong photoluminescence (PL) emission under low power pumping conditions, we investigated the influence of “suspending” a monolayer of tungsten diselenide (WSe2), a novel two-dimensional quantum material. Not only the PL intensity but also the fundamental photoluminescence quantum yield (PLQY) has exhibited a huge, order-scale enhancement through suspending; even surprisingly, we found the PLQY improvement to be far significant under small pumping powers and observed an exponential increase in tendency toward an even lower carrier density region. With its strong excitonic effect, suspended WSe2 offers a solution to reduce carrier trapping and participate in non-radiative processes. Moreover, in the low-power range, where SRH recombination dominates, suspended WSe2 exhibited a remarkably higher percentage of excitonic radiation compared to contacted WSe2. Herein, we quantitatively demonstrate the significance of the suspended WSe2 monolayer in a low carrier density region, highlighting its potential for developing compact, low-power quantum emitters in the future.

Leakage Mechanisms of sub-pA InGaAs/GaAs Nano-Ridge Waveguide Photodetectors Monolithically Integrated on a 300-mm Si Wafer

Abstract We report on a comprehensive temperature dependent dark current study of high-quality InGaAs/GaAs multi quantum well waveguide photodetectors monolithically integrated on silicon. They are integrated through metalorganic vapor-phase selective-area epitaxial growth in a 300-mm CMOS pilot line. Defects resulting from the metamorphic growth of III-V devices on Si make these devices susceptible to different leakage mechanisms at higher operating temperatures. For the high-temperature operation of complex photonics-electronics integrations, understanding the leakage mechanisms of the devices has critical significance. This will help to optimize designs promptly and ensure the reliability and longevity of such devices under extreme operating conditions. The photodetector devices exhibit dark currents below 1 pA, at room temperature and –1 V bias voltage, limited by the noise floor of the measurement setup. To resolve the different leakage mechanisms contributing to the dark current, the devices were measured at elevated temperatures and the results were cross-validated with device simulations. The devices exhibited very low dark currents, with a median below 0.1 nA at 195 °C, suggesting very high-quality material growth. Through device models, leakage mechanisms related to Shockley-Read-Hall (SRH) recombination at bulk volume defects are found to be the main factor contributing to the dark current. The surface SRH recombination is found to be limited, yet affecting the forward bias dark current due to the shortening of the diffusion paths of the majority carriers. Also, the device model shows that the actual dark currents at room temperature can be as low as 0.01 pA, more than 1-order lower than the measured levels. This study emphasizes the high quality of the III-V nano-ridge waveguide devices grown on Si, which can potentially expand the capabilities of silicon photonics platforms further.

Size‐Dependent Characteristics of InGaN‐Based Blue and Green Micro‐Light‐Emitting Diodes

This study focuses on investigating the size‐dependent characteristics (chip diameter: 100–10 μm) of InGaN‐based blue and green micro‐light‐emitting diodes (μLEDs) with respect to their electrical and optical properties. The LED's epistructure is grown using the metal–organic chemical vapor deposition technique, preceded by simulation and optimization using SiLENSe LED simulator. The cross‐sectional transmission electron microscopy study confirms the epistructure. The Photoluminescence mapping of the epistructure reveals that the blue emission is at 461 nm (full width at half maximum [FWHM] ≈ 15.5 nm) and the green emission is at 510 nm (FWHM ≈ 17.5 nm). The study analyzes the size‐dependent external quantum efficiency (EQE), optical power, and peak wavelength shift between blue and green μLEDs. The electroluminescence (EL) study reveals that the redshift of the EL peak wavelength of μLEDs is attributed to the release of strain at reduced chip sizes. The size‐dependent EQE study shows a reduction of EQE with shrunken chip size, attributed to the increase of nonradiative Shockley–Read–Hall recombination. Finally, the study estimates the characteristics temperature of the μLEDs using temperature‐dependent EL measurement, revealing that blue μLEDs exhibit a significantly large value of characteristic temperature ≈1926 K.

Carrier recombination in highly Al doped 4H-SiC: dependence on the injection conditions

We investigate carrier recombination mechanisms in heavily aluminum (Al) doped p-type 4H-SiC, a material crucial for power devices. The recombination mechanisms in Al-doped p-type 4H-SiC have remained unclear, with reports suggesting various possibilities. To gain insights, we employ photoluminescence (PL) measurements, particularly time-resolved PL (TR-PL), as they are well-suited for studying carrier lifetimes in heavily Al-doped p-type 4H-SiC. We examine the temperature and excitation intensity dependencies of TR-PL and PL spectra and discuss the underlying recombination mechanisms. We observe that the dominant recombination mechanism varies with injection conditions for the samples with Al concentration less than 1019 cm−3. Under low injection conditions, recombination via the Al acceptor level appears dominant, exhibiting weak temperature dependence. However, under high injection conditions, Shockley–Read–Hall recombination takes precedence, leading to shorter carrier lifetimes with increasing temperature. This temperature dependence implies that presences of the deep recombination centers with the small capture barrier for holes.

Nitrogen-displacement-related recombination centers generated by electron beam irradiation in n-type and p-type homoepitaxial GaN layers

Recombination centers originating from point defects generated by the displacement of N atoms in n-type and p-type GaN were investigated by analyzing Shockley–Read–Hall (SRH) recombination currents in homoepitaxial GaN p–n junctions. These defects were intentionally generated by electron beam (EB) irradiation at 137 keV. The net doping concentrations in p+–n junction diodes were not changed following irradiation although the levels in p–n+ junction diodes decreased as the EB fluence was increased. The SRH recombination current also increased with increases in the fluence. This work additionally evaluated the relationship between recombination lifetimes and trap concentrations obtained by deep level transient spectroscopy.

Strategy for perovskite solar cells approaching to S–Q limited efficiency

Despite recent substantial improvements in the efficiency of perovskite solar cells, the record efficiency of single-junction perovskite solar cells still falls short of the theoretical limiting efficiency predicted by Shockley–Queisser due to the presence of various loss mechanisms. It is essential to determine the dominant loss factors limiting power conversion efficiency () to clarify the future technical strategy towards ultimate efficiency. In this paper, we numerically investigate the impact of various loss mechanisms on the performance of realistic record perovskite solar cells, and identify the most important factors limiting the of perovskite solar cells. The results demonstrate that Shockley–Read–Hall recombination and series resistance, as well as optical loss are the most important factors for future improvement in efficiency.

Exploring Optoelectronic‐Thermal Coupling in Perovskite Solar Cells Utilizing Varied Hole Transport Layers

AbstractPerovskite solar cells (PSCs) have become a research hotspot both domestically and internationally due to their superior optoelectronic performance as a new type of thin‐film solar cell. One of the methods to enhance the performance of PSCs is the optimization of the hole transport layer(HTL). In this study, COMSOL Multiphysics simulation software is employed to model and simulate PSCs, and perform coupled simulations of the optical, electrical, and thermal properties of PSCs with different HTL. The simulations analyze the carrier concentration, Shockley–Read–Hall (SRH) recombination, electric field profile, and temperature distribution in the devices. The simulation results demonstrate that among the different HTL (CuO, Spiro‐OMeTAD, and NiO), NiO exhibited more favorable characteristics as a HTL for improving the photovoltaic conversion efficiency of PSCs. The photovoltaic conversion efficiency reached 17.14% with NiO as the hole transport layer, and the SRH recombination rate in PSCs based on NiO HTL of PSCs is lower than CuO and Spiro‐OMeTAD, facilitating efficient charge transport. Furthermore, the temperature distribution of PSCs is analyzed based on different HTL, and the results indicate that PSCs with NiO as the hole transport layer exhibited higher thermal stability.

Recent Research on Indium-Gallium-Nitride-Based Light-Emitting Diodes: Growth Conditions and External Quantum Efficiency

The optimization of the synthesis of III-V compounds is a crucial subject in enhancing the external quantum efficiency of blue LEDs, laser diodes, quantum-dot solar cells, and other devices. There are several challenges in growing high-quality InGaN materials, including the lattice mismatch between GaN and InGaN causing stress and piezoelectric polarization, the relatively high vapor pressure of InN compared to GaN, and the low level of incorporation of indium in InGaN materials. Furthermore, carrier delocalization, Shockley–Read–Hall recombination, auger recombination, and electron leakage in InGaN light-emitting diodes (LEDs) are the main contributors to efficiency droop. The synthesis of high-quality III-V compounds can be achieved by optimizing growth parameters such as temperature, V/III ratios, growth rate, and pressure. By reducing the ammonia flow from 200 sccm to 50 sccm, increasing the growth rate from 0.1 to 1 m/h, and lowering the growth pressure from 250 to 150 Torr, the external quantum efficiency of III-V compounds can be improved at growth temperatures ranging from 800 °C to 500 °C. It is crucial to optimize the growth conditions to achieve high-quality materials. In addition, novel approaches such as adopting a microrod crystal structure, utilizing the piezo-phototronic effect, and depositing AlN/Al2O3 on top of the P-GaN and the electron-blocking layer can also contribute to improving the external quantum efficiency. The deposition of a multifunctional ultrathin layers of AlN/Al2O3 on top of the P-GaN can enhance the peak external quantum efficiency of InGaN blue LEDs by 29%, while the piezo-phototronic effect induced by a tensile strain of 2.04% results in a 183% increase in the relative electroluminescence intensity of the LEDs. This paper also discusses conventional and inverted p-i-n junction structures of LEDs.

Bias-dependent degradation of single quantum well on InGaN-based light emitting diode

This paper investigates the factors that influence the efficiency and the reliability of InGaN-based light emitting diodes. The devices under test have a single InGaN quantum well, with a nominal emission wavelength of 495 nm. From the preliminary characterization, the L-I curve shows an anomalous slope mainly due to: i) high Shockley Read Hall recombination rate, and ii) low electron densities in the explored range of injection, as also confirmed by simulation. The reliability of the devices was investigated by performing a constant current stress test at J = 80 A/cm2 at room temperature. Optical degradation occurs with different trends, depending on the injection regime. For low injection levels, the optical power decay is monotonic. In the high injection range, for I > 10 mA, we can recognize different degradation phases. The optical degradation can be ascribed to the generation and relocation of defects in the active region, as also confirmed by DLOS measurement. The origin of degradation was also investigated by a stress test with photoluminescence measurement. The results suggest that the variation of the optical characteristics can be related to the variation of the intrinsic characteristics of the material.

CsSn0.5Ge0.5I3‐Based Lead‐Free Highly Stable Perovskite Solar Cell: Numerical Modeling for Estimating Performance Ceiling

CsSn0.5Ge0.5I3 perovskite is reportedly highly stable in ambient open air, lead free, and has excellent optoelectrical properties. An inverted p–i–n solar cell device based on this mixed SnGe perovskite utilizing the reported optical and electrical characteristics of the CsSn0.5Ge0.5I3 is simulated. This theoretical device under various recombination regimes to explore the performance ceiling of CsSn0.5Ge0.5I3 is put. An optimized configuration of CsSn0.5Ge0.5I3‐based perovskite solar cell shows an efficiency of 29% under the impact of only intrinsic recombination losses such as radiative (with radiative recombination coefficient of 10−11) and Auger recombination (recombination coefficient of 10−27). When extrinsic factors are considered, such as resistance losses (series resistance as high as 2 Ω cm2 and shunt resistance as low as 1000 Ω cm2), efficiency decreases to 27.5%. The efficiency is 20% when trap‐assisted Shockley–Read–Hall recombination is considered with voltage loss (V Loss) of 0.5 V. Similarly, V Loss = 0.6 V in V OC restricts device efficiency to 15%. Finally, an efficiency waterfall chart summarizes the CsSn0.5Ge0.5I3, efficiency under different extrinsic losses, and the performance loss analysis, providing an optimal design. The results summarized here are expected to be helpful and prompt experimentalists to fabricate this stable lead‐free perovskite solar cell.

Effect of Mg doping on carrier recombination in GaN

Time-resolved photoluminescence measurements have been performed on Mg-doped GaN for Mg concentrations in the low- to mid-1019 cm−3. As-grown and annealed (600–675 °C) samples were studied. In the as-grown samples, the nonradiative carrier lifetime was found to be about 200 ps and nearly independent of the Mg concentration. Upon annealing, the carrier lifetimes shorten to ∼150 ps but, again, show little dependence on the annealing temperature. The analysis of possible Shockley–Read–Hall recombination centers and their behavior during doping and annealing suggests that the main nonradiative recombination center is the Mg–nitrogen vacancy complex. The weak dependence of the PL decay times on temperature indicates that carrier capture into this center has a very low potential barrier, and the nonradiative recombination dominates even at low temperatures.

Effects of high-dose 80 MeV proton irradiation on the electroluminescent and electrical performance of InGaN light-emitting diodes

The paper reports on the degradation of InGaN/GaN Blue LED submitted to proton irradiation at 80 MeV and various fluences (4×1013 p cm−2 and 1×1014 p cm−2). After irradiation, we found a decrease in light output power and the external quantum efficiency with fluence. Photoluminescence (PL) measurements exhibited that the peak position at 400, 447 and 568 nm remained unchanged, only the peak intensity decreased. The intensity of the blue emission reduced by 75%, indicating that the active region degraded seriously; the intensity from In x Ga1-x N (x = 0.11) reduced more than two times in comparison with the blue emission, implying that proton irradiation affected In x Ga1-x N more seriously than InGaN/GaN MQWs. The degradation of LED is ascribed to the increase in the defect-related Shockley–Read–Hall recombination after 80 MeV proton irradiation with higher fluence.

Simulation of Capacitorless DRAM Based on the Polycrystalline Silicon Nanotube Structure with Multiple Grain Boundaries.

In this study, a capacitorless one-transistor dynamic random-access memory (1T-DRAM), based on polycrystalline silicon (poly-Si) nanotube structure with a grain boundary (GB), is designed and analyzed using technology computer-aided design (TCAD) simulation. In the proposed 1T-DRAM, the 1T-DRAM cell exhibited a sensing margin of 422 μA/μm and a retention time of 213 ms at T = 358 K with a single GB. To investigate the effect of random GBs, it was assumed that the number of GB is seven, and the memory characteristics depending on the location and number of GBs were analyzed. The memory performance rapidly degraded due to Shockley-Read-Hall recombination depending on the location and number of GBs. In the worst case, when the number of GB is 7, the mean of the sensing margin was 194 µA/µm, and the mean of the retention time was 50.4 ms. Compared to a single GB, the mean of the sensing margin and the retention time decreased by 59.7% and 77.4%, respectively.

Modification of Hydrophobic Self‐Assembled Monolayers with Nanoparticles for Improved Wettability and Enhanced Carrier Lifetimes Over Large Areas in Perovskite Solar Cells

The development of perovskite solar cells (PSCs) with low recombination losses at low processing temperatures is an area of growing research interest as it enables compatibility with roll‐to‐roll processing on flexible substrates as well as with tandem solar cells. The inverted or p–i–n device architecture has emerged as the most promising PSC configuration due to the possibility of using low‐temperature processable organic hole‐transport layers and more recently, self‐assembled monolayers such as [4‐(3,6‐dimethyl‐9H‐carbazol‐9‐yl)butyl]phosphonic acid (Me‐4PACz). However, devices incorporating these interlayers suffer from poor wettability of the precursor leading to pin hole formation and poor device yield. Herein, the use of alumina nanoparticles (Al2O3 nanoparticles (NPs)) for pinning the perovskite precursor on Me‐4PACz is demonstrated, thereby improving the device yield. While similar wettability enhancements can also be achieved by using poly[(9,9‐bis(3′‐((N,N‐dimethyl)‐N‐ethylammonium)‐propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)]dibromide (PFN‐Br), a widely employed surface modifier, the incorporation of Al2O3 NPs results in significantly enhanced Shockley–Read–Hall recombination lifetimes exceeding 3 μs, which is higher than those on films coated directly on Me‐4PACz and on PFN‐Br‐modified Me‐4PACz. This translates to a champion power conversion efficiency of 19.9% for PSCs fabricated on Me‐4PACz modified with Al2O3, which is a ≈20% improvement compared to the champion device fabricated on PFN‐Br‐modified Me‐4PACz.

Stability of Cu(InxGa1−x)Se2 Solar Cells Utilizing RbF Postdeposition Treatment under a Sulfur Atmosphere

Alkali halide postdeposition treatments (PDTs) have become a key tool to maximize efficiency in Cu(InxGa1−x)Se2 (CIGS) photovoltaics. RbF PDTs have emerged as an alternative to the more common Na‐ and K‐based techniques. This study utilizes temperature‐dependent current–voltage (JVT) measurements to study a unique RbF PDT performed in a S atmosphere. The samples are measured before and after 6 months in a desiccator to study device stability. Both samples contain Na and K which diffuse from the soda–lime glass substrate. A reference sample and a RbF + S PDT sample both show the development of a rear contact barrier after aging. The contact barrier is higher for the RbF + S PDT sample, leading to decreased current in forward bias. Series resistance is also higher in the RbF + S PDT device which leads to lower fill factor. However, after aging the reference sample has a larger decrease in open‐circuit voltage (VOC). Ideality factor measurements suggest Shockley–Read–Hall recombination dominates both samples. VOC versus temperature and a temperature‐dependent activation energy model are used to calculate diode activation energies for each sample condition. Both techniques produce similar values that indicate recombination primarily occurs within the bulk absorber.

Modeling Lattice Matched Dilute Nitride Triple and Quadruple Junction Solar Cells on Virtual SiGe Substrate

A lattice matched triple junction solar cell (TJSC) structure with a GaAs0.58 P0.42 top cell and bandgap tunable GaNxAs1-x-zPz middle and bottom cells on virtual SiGe substrate is proposed in this study. SiGe/Si substrate is preferred as it is a low-cost substrate and because it provides a lattice constant at which bandgap tunable dilute nitride materials that are appropriate for highly efficient multijunction solar cells can be obtained. By changing the nitrogen content in GaNxAs1-x-zPz, the bandgap of the middle and bottom subcells is adjusted to the optimum values. The bandgap of the top cell is constant at 1.95 eV. Three models with different values of surface recombination velocities and Shockley–Read–Hall recombination lifetimes are applied to the presented TJSC structure. Peak efficiencies of 48.9%, 40.6% and 33.7% are achieved at EG2 = 1.45 eV and EG3 = 1.04 eV for Model 1, EG2 = 1.45 eV and EG3 = 1.15 eV for Model 2, and EG2 = 1.5 eV and EG3 = 1.17 eV for Model 3, respectively. A fourth bandgap adjustable GaNxAs1-x-zPz junction is inserted into the system and a significant improvement is obtained under high sun concentration for Models 1 and 2. The presented original results are very promising because the variable bandgaps provide very efficient absorption of incoming spectrum.

Numerical device modeling for direct Z-scheme junctions using a solar cell simulator

Carbon capture and utilization (CCU) is a promising solution for reducing reliance on fossil fuels and incentivizing the capture of CO2. A key requirement for CCU is the development of effective photo/electrocatalysts with high CO2 reduction activity that can produce high-value products. Direct Z-scheme heterojunctions named after their charge transfer mechanism, use sunlight to conduct various photocatalytic reactions, similar to photosynthesis in plants. Solar cell simulation techniques can be used to obtain material properties and insights into the electronic characteristics of these materials. By solving semiconductor differential equations that model the behavior of semiconductors under different light intensities and applied biases, the solar cell simulator program (SCAPS) can evaluate the energy band edges, carrier concentrations, and output characteristics of the device. In this study, a method is proposed for modeling direct Z-scheme junctions in SCAPS by simulating the Shockley Read Hall (SRH) recombination using defect densities at the interface of the recombination junction (RJ). An example using a TiO2/CdIn2S4 Z-scheme junction is presented and the impact of defects on the performance of the junction is discussed. It is presented that the high recombination rates at the interface via these defects improve the device performance.

Traps inhomogeneity induced conversion of Shockley–Read–Hall recombination in NiO/β-Ga2O3 p+–n heterojunction diodes

In this Letter, the trap inhomogeneity within β-Ga2O3 is correlated with the conversion of Shockley–Read–Hall (SRH) recombination in NiO/β-Ga2O3 p+–n heterojunction diodes. For the virgin epi-wafer, both near-surface traps E2 (EC-0.82 eV) and E3 (EC-1.11 eV) and bulk E2* traps (EC-0.76 eV) are identified by a transient capacitance analysis, and the corresponding forward current–voltage characteristics of diodes are well fitted in the framework of field-dependent SRH recombination. The SRH recombination rates for E2, E3, and E2* traps are determined to be 1.3 × 107, 8.6 × 108, and 2.4 × 108 s−1, respectively. In this circumstance, carrier transport under forward bias is governed by trap-assisted tunneling through E3 traps with high recombination rates, and the hysteresis is pronounced. With the removal of the defective surface layer, E2 and E3 traps are almost completely eliminated, together with the reduced density of E2* traps to 5.6 × 1014 cm−3. The resultant diode performs an improved rectification ratio of >1011 at ±3 V and an enhanced reverse breakdown voltage of 1692 V. The elimination of near-surface traps leads to the conversion of carrier transport into the conventional SRH recombination, accompanied by the negligible forward hysteresis characteristics. The established fundamental correlation of carrier transport and traps within Ga2O3 is beneficial to develop a high-performance power rectifier toward practical applications.

Bandgap Fluctuations, Hot Carriers, and Band‐to‐Acceptor Recombination in Cu2ZnSn(S,Se)4 Microcrystals

Temperature and laser power dependencies of the band‐to‐acceptor recombination in Cu2ZnSn(S x Se1−x )4 (x = 0.7) microcrystals, which exhibit large bandgap energy fluctuations, are studied. The average depth of these fluctuations is approximately 79 meV. The shape of the corresponding wide photoluminescence (PL) band is analyzed using a modified localized‐state ensemble model. The temperature dependence of this PL band is demonstrated to be influenced by the redistribution of holes between potential wells in the valence band with varying depths. The shape of this band at different temperatures is well fitted when an effective carrier temperature is introduced. This temperature is found to be approximately 300 K higher than the lattice temperature in the samples, and it is mainly caused by the very short minority carrier lifetime. According to the laser power‐dependent PL studies, there is a consistent reduction in the effective carrier temperature as the laser power increases. This phenomenon is explained by the dominance of nonradiative Shockley–Read–Hall recombination at lower temperatures.