Donor-acceptor Recombination Research Articles

PHOTOELECTRICAL PROPERTIES OF CdMnSe THIN FILMS

The studied semiconductor structure for photovoltaic cells is composed of SnO2-coated glass and CdMnSe thin film. A study is made by examining the photoluminescence from the surface of the CdMnSe thin film with laser power and sample temperature for an as-grown, then an air-annealed thin film and undergone CdCl2 treatment. Thin films of Cd1-xMnxSe (x=0.02) were grown on a glass substrate. The lifetime of charge carriers under pulsed illumination was determined from the kinetic decay of the photocurrent. The study of relaxation curves of nonequilibrium photoconductivity under the influence of laser radiation confirmed the presence of two recombination channels - intrinsic and impurity. Photocurrent relaxation occurs through fast and slow recombination channels. The fast relaxation time τ = 6 μs associated with the intrinsic transition and the slow relaxation time is due to impurity excitation and τ = 22 μs. The photoluminescence spectra of thin films of Cd1-xMnxSe (x=0.02) were studied. In the photoluminescence study, two maxima are observed due to donor-acceptor recombination and intracenter transition of Mn atom.

Donor–Acceptor Recombination Emission in Hydrogen‐Terminated Nanodiamond

AbstractFluorescence spectra of nanodiamonds synthesized at high pressure from adamantane and other organic compounds show narrow (≈1 nm) lines of unknown origin over the spectroscopic range from ≈500 to 800 nm. The study proposes and experimentally confirms the hypothesis that these lines are related to radiative recombination of donor–acceptor pairs (DAP). According to the experimental data, these pairs can be formed from donor‐like substitutional nitrogen present in the diamond lattice and 2D acceptor layer resulting from the effect of transfer doping on the nanodiamond surface. A peculiar behavior of the narrow lines is identified within the temperature range of 100–10 K: their energy position slightly shifts downward, and the majority of the lines divide into two or more components as the temperature decreases. The lines are shown to be predominantly associated with single photon emitters, with an emission rate exceeding 1 million counts s−1 at room temperature. A new narrowband source of room‐temperature fluorescence found in hydrogen‐terminated nanodiamonds push horizons for quantum optical technologies related to the development of single photon emitters and temperature nanosensors.

Systematic Tuning of Persistent Luminescence in a Quaternary Wurtzite Crystal Through Synergistic Defect Engineering

AbstractPersistent luminescence (PersL), characterized by continuous light emission after cessation of excitation, finds enormous applications in night displays, optoelectronics, and biomedicine. Despite the long history and a recent renaissance of PersL research, there still lacks a versatile approach for deliberate control over PersL in a single material system, which is crucial for mechanistic understanding and rational design of PersL. Herein, a strategy for the systematic tuning of PersL in the wavelength, time, and temperature domains in a wurtzite CaZnOS crystal, based on synergistic defect engineering (i.e., simultaneous control of activator/trap states and trap‐filling process) through combinatorial doping in the double cationic sites, is presented. This design principle can be harnessed to produce PersL in a vast collection of emitters with distinct electronic transitions, including ns2‐nsnp, 3d–3d, 4f–4f, and donor–acceptor recombination, which is inaccessible to the existing material systems. The results highlight that the strategy of synergistic defect engineering can provide unprecedented PersL properties with stimulus‐responsive features for information encryption and photoexcitation‐free optical thermometry.

Magnetic‐Force‐Induced‐Luminescent Effect in Flexible ZnS:Cu/PDMS/NdFeB Composite

AbstractThe force‐induced light‐emitting phenomenon in polymer composites plays an important role in the soft electronic field due to its display function. Here, a magnetic‐force‐induced‐luminescence (MFIL) effect is reported in ZnS:Cu particle‐doped polydimethylsiloxane incorporated with a NdFeB magnetic tip mass for real‐time incident magnetic field strength light‐emitting display. Investigations show that the luminescence intensity increases nearly linear in response to the applied AC magnetic field, HAC; meanwhile, the minimum HAC for inducing MFIL is as low as 0.1 mT (1 Oe) at the resonance. The MFIL effect is 1000 times better and more energy‐efficient than the best result published previously. The findings, thus, indicate that the MFIL effect could serve as an effective method for light‐emitting display triggered by HAC; MFIL essentially originates from the donor–acceptor recombination between shallow donor level and the t2 level of Cu2 in ZnS:Cu semiconductor particles. The present results could, thus, provide a viable pathway toward multifunctional flexible electronic designs and applications, especially toward those for the real‐time visualization of remote magnetic field sensing.

Growth temperature induced changes of luminescence in epitaxial BN: from colour centres to donor-acceptor recombination.

Defects play a very important role in semiconductors and only the control over the defect properties allows the implementation of materials in dedicated applications. We present an investigation of the UV luminescence of defects in hexagonal boron nitride (h-BN) grown by Metal Organic Vapor Phase Epitaxy (MOVPE). Such intentionally introduced defects are important for applications like deep UV emission and quantum information. In this work, we performed photoluminescence and cathodoluminescence experiments on a set of h-BN layers grown by MOVPE at different growth temperatures (tgr). The obtained defect-related spectra in the ultraviolet range include well-known lines at about 230 nm (X230, hν = 5.4 eV) and 300 nm (C300 - the brightest one, hν = 4.14 eV) as well as a rarely observed band with a zero-phonon line at 380 nm (C380, hν = 3.24 eV). The C300 and C380 bands have the characteristic of a color centre showing sharp lines (0.6 nm width) at 5 K. These lines are most probably an internal transition of carbon-related defects. We show that for samples grown at high temperatures (tgr > 1200 °C), the lines related to the color centres C are replaced by broad bands at 330 nm and 400 nm, which we marked as D330 and D400, respectively. The D bands have similar central energies to the C bands but extend over a large energy range, so we propose that the D emission is due to a shallow donor to deep acceptor recombination. Time-resolved photoluminescence analysis determined the lifetimes of the individual lines in the range from 0.9 ns (C300), 1.8 ns (C380) to 4 ns (D400). The C300 and C380 color centre bands are composed of a series of characteristic lines that are due to the interaction with phonons. The E1u (198 meV) and A2u (93 meV) phonon replicas have been identified.

Stimulated emission in the heavily doped Al-=SUB=-0.68-=/SUB=-Ga-=SUB=-0.32-=/SUB=-N : Si structures with transverse optical pumping at room temperature

The broadband stimulated emission in the spectral range λ=380-700 nm with the inhomogeneous broadening has been experimentally obtined in the heavily doped Al0.68Ga0.32N : Si structures grown by molecular beam epitaxy. The behavior of the intensities and spectra of stimulated emission from the edge of the active element with transverse pulsed pumping by radiation with λ=266 nm, measured at room temperature, demonstrate the threshold behavior and optical gain. For stimulated emission with a maximum at λ=500 nm, the minimum threshold pump power density was 6.5 kW/cm2 for excited region length of 1.5 mm. The parameters and contributions of the two main processes e-A and D-A of radiative recombination in the excited structures for stimulated emission and optical gain are studied. Keywords: stimulated emission, heavily doped AlxGa1-xN structures, luminescence, optical gain, donor-acceptor recombination.

Photoluminescence of Ag8SnSe6 argyrodite

A basic study of the low-temperature photoluminescence of an Ag8SnSe6 argyrodite compound is reported. Measurements were performed on wafers grown by the direct melting of a high-purity stoichiometric mixture of elementary Ag, Sn, and Se in a sealed silica ampoule. Two peaks with maxima located at 0.85 and 0.95 eV were visible in the photoluminescence spectra of an Ag8SnSe6 argyrodite. The temperature and excitation dependences of the dominant peak at 0.85 eV suggest that this transition can be associated with donor-acceptor recombination. The activation energies of the defects involved in this transition were calculated based on temperature-dependent photoluminescence and transmission measurements. We found the ionization energies to be at 44 and 72 meV for the shallower and deeper defects, respectively. The second peak in the spectra at 0.95 eV was assigned to a band-to-band transition or a transition between band tails.

Temperature-dependent photoluminescence and decay times of different phases of grown TiO2 nanoparticles: Carrier dynamics and trap states

Three different phases, namely anatase, mixed and rutile phases of TiO2 nanoparticles (NPs) were developed with varying temperatures from 400 to 900 °C and confirmed using various characterization techniques. The XRD analysis of TiO2 NPs in temperature range of 290 to 77 K with no significant changes predict the thermally stable NPs. Photoinduced carrier dynamics of TiO2 NPs were investigated by the temperature dependence (TD) photoluminescence (PL) and TD time-resolved PL (TRPL) decays. With varying temperatures from 290 to 77 K, the anatase phase exhibits an additional and dominant 530 nm PL band. However, the mixed and rutile phases show three well-resolved PL bands, including 420 nm, 530 nm and near-infrared (NIR) bands at 820 nm at a lower temperature. Again, 530 nm band dominated for mixed-phase.In contrast, for the rutile phase, the 820 nm band dominated at <100 K. The PL lifetime of the 420 nm band is nearly a single exponential for all the phases. And is also true for the 530 and 820 nm PL bands, but bi-exponential for ≤100 K. Both the PL and TRPL results predict the presence of trap states in TiO2 NPs for anatase and rutile phases. The PL is originated due to donor-acceptor recombination, whereas oxygen vacancies served as donor and hydroxyl groups serve as accepter sites. The NIR band is attributed to the trapped electrons in rutile TiO2, which recombine with free holes and intrinsic defects. Also, the trapped electrons were generated in one of two ways: direct trapping or trap-to-trap hopping. The carrier dynamic in NPs depends on the trap states as the photoexcited carriers transfer into surface sites which competes with non-radiative and radiative recombinations during the relaxation process. Thus, the findings show that the trap states in TiO2 can significantly influence TiO2 photocatalytic activity when exposed to appropriate light.

Composition-Controlled Synthesis of Near-IR-Light-Emitting Ag-Ιn-Ga-Se Nanocrystals for Biological Imaging

Colloidal semiconductor nanocrystals have been intensively developed for the application to photovoltaics, light-emitting diodes, electroluminescent device, and photoluminescent markers for bio-imaging. Recently, low-toxic I-III-VI semiconductor-based multinary chalcogenide nanocrystals have attracted much attention as a promising alternative for Cd-based ones, because these nanocrystals are composed of less-toxic elements and exhibited intense photoluminescence (PL) in the visible and near-IR wavelength regions. In our previous paper, we reported that chemically synthesized Zn-Ag-In-S nanocrystals exhibited a broad PL peak (FWHM > 100 nm) originating from donor-acceptor pair radiative recombination, the wavelength of which was tunable from ca. 500 to 800 nm by changing the particle size and the chemical composition.[1] However, these multinary nanocrystals did not exhibit a band-edge emission, though narrowing PL peak has been earnestly desired for luminescent applications. In this study, we report the preparation of novel multinary Ag-In-Ga-Se nanocrystals via solution phase synthesis and control the peak wavelength of band-edge emission in the range from visible to near-IR lights. We also demonstrated the usefulness of thus-obtained Ag-In-Ga-Se nanocrystals for in vivo bio-imaging.[2] Semiconductor nanocrystals composed of Ag-In-Ga-Se (AIGSe) solid solution were prepared by the thermal decomposition of corresponding metal salts and selenourea in a hot mixture solution of oleylamine/1-dodecanethiol under an N2 atmosphere. The molar ratios of precursors were varied with the synthesis of Ag0.67InyGa(1-y)Se2 (AIGSe) in mind. The individual XRD peaks of thus-obtained AIGSe nanocrystals were located between those of tetragonal AgInSe2 and AgGaSe2 crystal structures and shifted to a higher angle with a decrease in the y value, indicating that the Ga3+ fraction in the Ag(In,Ga)Se2 solid solution increased with a decrease in the y value in preparation. TEM measurements revealed that spherical nanocrystals were formed, the average size of which were varied in the range of 3~5 nm depending on the chemical composition. The PL spectra of as-prepared AIGSe nanocrystal exhibited both a narrow band-edge emission peak and a broad defect-site emission peak. By surface-coating AIGSe nanocrystals with GaSx (AIGSe@GaS x ), a broad PL peak was remarkably diminished especially for y = 0.25-0.5, owing to the removal of the surface defect sites. With a decrease in the y value, that is, with an increase in the Ga/In ratio of nanocrystals, the peak wavelength of band-edge emission of AIGSe@GaS x nanocrystals was blue-shifted from 890 to 610 nm because of the increase in their energy gap. The PL quantum yield (QY) was enlarged by the GaS x shell coating, in which the maximum PL QY of 38% was obtained for the PL peak at 800 nm AIGSe@GaS x of y = 0.7. Thus-obtained nanocrystals were successfully used as near-IR PL probes for three-dimensional in vivo bioimaging, in which the wavelengths of excitation and detection lights could be selected in the first biological window. The imaging signals were clearly detected from AIGSe@GaS x nanocrystals injected into biological tissues by ca. 5 mm in depth. Reference Torimoto, et al., J. Phys. Chem. C, 2015, 119, 24740-24749. Torimoto, et al., ACS Appl. Nano Mater . 2020, 3, 3275-3287.

Arsenic Doping Upon the Deposition of CdTe Layers from Dimethylcadmium and Diisopropyltellurium

The incorporation and activation of arsenic from tris(dimethylamino)arsine in CdTe layers grown by metal-organic chemical vapor deposition from dimethylcadmium and diisopropyltellurium on GaAs substrates are investigated. The incorporation of arsenic into CdTe depends on the crystallographic orientation of the layers and increases in the series (111)B → (100) → (310). The arsenic concentration in the CdTe layers is proportional to the tris(dimethylamino)arsine flow rate at a power of 1.4 and increases with decreasing diisopropyltellurium/dimethylcadmium ratio from 1.4 to 0.5. After deposition, the CdTe:As layers have p-type conductivity with an arsenic concentration of 1 × 1017–7 × 1018 cm–3 and a hole concentration of 2.7 × 1014–4.6 × 1015 cm–3, respectively; the fraction of electrically active arsenic does not exceed ~0.3%. After annealing in argon (250–450°C), the highest hole concentration is 1 × 1017 cm–3, and the arsenic activation efficiency is ~4.5%. The ionization energy of arsenic determined from the temperature dependence of the hole concentration is in the range of 98–124 meV. The low-temperature photoluminescence spectra of the layers have an emission peak with an energy of ~1.51 eV, which can be attributed to donor–acceptor recombination, where AsTe is an acceptor with an ionization energy of ~90 meV.

Donor-acceptor nature of orange photoluminescence in AlN

Recombination dynamics, photoluminescence and photoluminescence excitation spectra have been investigated for 1.9 eV photoluminescence band in AlN in the temperature range of 5–650 K. The recombination dynamics for the 1.9 eV photoluminescence band has been described by a model of donor-acceptor recombination with taking into account a broadening due to electron coupling with local lattice vibrations of a deep level defect. The experimental results have been compared with density functional theory calculations of luminescence peak energies and line shapes of band to defect and donor-acceptor transitions, and possible origin of the orange photoluminescence band in AlN has been discussed.

Акцепторное легирование мышьяком при осаждении слоев CdTe из диметилкадмия и диизопропилтеллура

The incorporation and activation of arsenic from tris(dimethylamino)arsine in CdTe layers grown by metalorganic chemical vapor deposition with dimethylcadmium and diisopropyltellurium on GaAs substrates are investigated. Arsenic incorporation into CdTe to depend on the crystallographic orientation of the layers and increases in the order (111)B&lt;(100)&lt;(310). Arsenic concentration in the CdTe layers is proportional to the tris(dimethylamino)arsine flow rate to the power of 1.4 and an increase with decrease of the diisopropyltellurium/dimethylcadmium ratio from 1.4 to 0.5. The as-grown CdTe:As layers had p-type conductivity with arsenic and hole concentrations of 1·1017–7·1018 and 2.7·1014–4.6·1015 cm–3, respectively, but the arsenic activation efficiency not exceeding 0.3%. After annealing in argon flow (250–450 ° C) the highest hole concentration and arsenic activation efficiency were 1·1017 cm–3 and ~4.5 % respectively. The ionization energy of arsenic determined from the temperature dependence of the hole concentration was in the range of 98–124 meV. Low-temperature photoluminescence spectra of the layers showed an emission peak with energy of 1.51 eV, which can be attributed to donor-acceptor recombination, where the acceptor is AsTe with ionization energy about 90 meV.

Optical Gain in Heavily Doped AlxGa1 –xN:Si Structures

Gain characteristics of heavily doped AlxGa1 –xN/AlN:Si structures with c x = 0.65 and 0.74 have been studied under pulsed optical pumping by Nd:YAG laser radiation at wavelength λ = 266 nm. The absolute values of the optical gain measured at spectral maximum of the room-temperature luminescence spectrum reach (0.5–6) × 103 сm–1 at an pumping power density of 8–600 kW/cm2. Cross sections of the radiative and donor–acceptor recombination are close to each other and exceed 1016 cm2.

Synthesis and optimization of emission characteristics of water-dispersible ag-in-s quantum dots and their bactericidal activity

Developing novel aqueous-soluble quantum dots (QDs) can create new opportunities for better biological utilization. In the present work, novel, high emissive and biocompatible N-acetyl-L-cysteine-capped Ag-In-S QDs (as an I-III-VI structure) were prepared in a facile and straightforward way. The dominance of the strong confinement regime was observed due to the very small size of nanoparticles, which was smaller than their excitonic Bohr radius. To prepare reproducible Ag-In-S QDs, their emission characteristics were improved by optimizing the experimental variables which resulted in the enhancement of their emission quantum yield to near 32% at 615 nm. The absorption and emission results support the contribution of band edge-independent radiative recombination pathways for charge carriers in the prepared Ag-In-S QDs. The possible mechanisms for such donor-acceptor recombination were also discussed. To explore the antibacterial ability of the Ag-In-S QDs, their bactericidal activity was evaluated against different types of Gram-positive (Staphylococcus aureus and Bacillus subtilis) and Gram-negative (Escherichia coli and Salmonella enterica) bacteria. Precise measurements confirmed a remarkable bactericidal activity of Ag-In-S QDs against the different pathogenic bacteria even at low concentration of QDs (15 μg/mL). It was found that the QDs are more effective on Gram-negative bacteria. While the preparation method was simple and cost-effective, the as-synthesized QDs were highly emissive and stable with significant antibacterial activity. This demonstrates the great potential of present Ag-In-S QDs for future hygienic and medical purposes.

Effect of Charge Carrier Relaxation on Donor-Acceptor Recombination Spectra Taking into Account Coulomb Correlations

This study presents the results of numerical simulation of donor-acceptor recombination spectra in compensated semiconductors taking into account electrostatic fluctuations associated with the presence of ionised impurities. The presence of Coulomb correlations in a system of partially ionised impurity centers results in distinctive features appearing in recombination spectra, depending on charge-carrier energy relaxation. The authors have considered the following limiting cases: absence of relaxation, partial relaxation of majority and minority charge carriers, as well as complete relaxation of a system of electrons and holes localized on impurities. The results obtained through numerical simulation have been interpreted using a previously developed analytical model, in which contributions to recombination from equilibrium and photoexcited charge carriers are considered separately. It has been shown that, under certain experimental conditions, emission lines corresponding to these contributions can be spectrally resolved.

Оптическое усиление в сильнолегированных структурах Al-=SUB=-x-=/SUB=-Ga-=SUB=-1-x-=/SUB=-N : Si

The gain characteristics of heavily doped AlxGa1-xN/AlN: Si structures with x = 0.65 and 0.74 under optical pumping by a pulsed Nd:YAG laser radiation with lambda= 266 nm have been experimentally studied at room temperature. The absolute values of the optical gains are (0.5–6)*10^3 сm-1 in the maximum of the luminescence spectrum at the excitation power density (8–600) kW/cm2. The obtained cross sections for the radiative and donor–acceptor recombination coincide with each other and exceed the 10^(-16) сm2.

Non-radiative coupled donor-acceptor pair recombination in nanostructures based on nitrides and related phenomena

It has been clarified that several peculiarities of I-V characteristics at U < 1.5 V and low frequency noise dependences in InGaN/GaN nanostructures for green and blue spectral range as well as in Schottky barriers in AlGaN/GaN HEMT nanostructures are evoked by the non-radiative coupled deep donor-acceptor pair recombination. The strong contribution of the non-radiative donor-acceptor recombination in the degradation of the nanostructures properties has been confirmed experimentally.

Spectrally resolved thermoluminescence in UV excited hexagonal boron nitride nanopowder

Thermally stimulated luminescence (TSL) excitation and emission processes in h-BN nanopowders after UV irradiation were studied. TSL showed the highest response within the 5.4 eV band. 3.0 and 3.9 eV bands, resulting from the radiative donor-acceptor recombination between the electron (1B-H ON-centers) and the hole traps (CN-center), were found. TSL curves quantitative analysis in the context of general order kinetics was made. It was shown that 1B-centers had 0.85±0.05 eV activation energy and were responsible for the TSL peak at 350±10 K. Band structure for TSL excitation and emission mechanisms in h-BN nanopowder was suggested.

Two components of donor-acceptor recombination in compensated semiconductors: Analytical model of spectra in the presence of electrostatic fluctuations

We report numerical and analytical studies of the donor-acceptor recombination in compensated semiconductors. Our calculations take into account random electric fields of charged impurities which are important in non zero compensation case. We show that the donor-acceptor optical spectrum can be described as a sum of two components: monomolecular and bimolecular. In the low compensation limit we develop two analytical models for both types of the recombination. Also our numerical simulation predicts that these two components of the photoluminescence spectra can be resolved under certain experimental conditions.

Carrier dynamics in the potential-induced degradation in single-crystalline silicon photovoltaic modules

In this study, transient diffuse reflectance spectroscopy (TDRS) and electroluminescence (EL) analysis have been employed to clarify the carrier dynamics in potential-induced degradation (PID) in single-crystalline Si (sc-Si) solar cell. We first localized the PID-affected region in terms of degradation intensity on the modules on the basis of EL. The carrier dynamics in that region are then studied and clarified in terms of carrier lifetime, defect level, and photogenerated carrier density. Our results suggest that carrier relaxation in a fresh solar cell proceeds via band to band and/or shallow and deep donor–acceptor recombination. However, the dominant recombination in solar cells with PID is intercenter charge transfer via shallow-to-deep and/or deep–deep defects for which the carrier lifetime decreased drastically. Also, it is found that the carrier dynamics near the surface and bulk do not progress similarly as confirmed using 532- and 1064-nm-wavelength pumps.