Band Gap Of ZnSe Research Articles

SYNTHESIS OF STRUCTURED ZINC SELENIDE FOR OPTOELECTRONIC APPLICATIONS

In this paper, synthesis of Zinc Selenide (ZnSe) based photovoltaic materials deposited by electrode position method. The material lms have been characterized for their optical properties using UV-VIS spectrophotometer with wavelength range of 300 nm – 900 nm and electrical conductivity using photoelectrochemical (PEC) cell measurement. The conductivity type of the electrodeposited materials was investigated together with the tuning of the optical phenomena. The materials deposited were obtained by varying deposition time from 5 minutes to 15 minutes for ZnSe. It was observed that the optical properties of the materials increased with an increase in the time of deposition. The optical band gap of ZnSe was found to be in the range between 2.03 and 2.46 eV. The PEC signal results revealed ZnSe as an n-type material.

Magnesium ions enhanced core-shell lattice matching for Narrow-Band green emission indium phosphide QDs

Indium phosphide QDs have emerged as a promising candidate for the next generation optoelectronic applications. However, the optical performance of InP QDs still lags behind that of CdSe-based QDs, partly due to surface traps induced by the lattice mismatch between InP and ZnSe. Herein, based on (DMA)3P, we designed an alloyed inner-shell structure of InP/Zn(Mg)Se/ZnS QDs. The dual-function mechanism of the Zn(Mg)Se was revealed, which effectively mitigates the lattice mismatch between the core and shell toreduce the emission of surface defect states, resulting in narrowed emission peaks (FWHM ∼ 36 nm). While the increased band gap of Zn(Mg)Se confines the exciton delocalization from core to shell, thereby reducing the non-radiative relaxation of carriers at the defect states in the shell. This discovery provides a strategy to improve the color purity and luminescence efficiency of InP QDs. By combining blue LED chips with InP/Zn(Mg)Se/ZnS, a white light-emitting diode (QLED) with a high luminous efficiency of 63 lm/W was obtained. Furthermore, the realization of QDs arrays with 10 μm pixel dots by inkjet printing technology and the fabrication of white-light emitting Micro-LEDs by combining QDs films with Micro-LED chip arrays demonstrate the potential application of InP QDs in high-efficiency optoelectronic devices (LEDs/micro-LEDs).

The FP-LAPW/GAM-MPW1K approach: a reliable abinitio method for calculating the band gap of II-VI semiconductors monochalcogenides.

The bandgap of metal monochalcogenides (MMCs) is a key property that governs their physical and chemical properties. Accurate measurement of the bandgap is essential for a range of applications, including optoelectronics and photovoltaics. However, many theoretical approximations fail to accurately calculate the bandgap for MMCs, making it difficult to obtain precise values. This study investigated the suitability of the FP-LAPW/GAM-MPW1K scheme for determining the bandgap of MMCs. The investigation included lattice parameters, bandgap, band structure, and density of states, which were compared against both previous theoretical calculations and available experimental data. The findings of the study indicate that the FP-LAPW/GAM-MPW1K approach accurately calculates the bandgap value of MMCs by efficiently treating d-state electrons. The results are consistent with prior studies, confirming the method's reliability in determining the bandgap of these semiconductors. our study used the GAM-MPW1K functional and the full potential linearized augmented plane wave method (FP-LAPW) in the ELK code to calculate the lattice parameters, electronic band structure, and bandgap of ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe compounds in the wurtzite structure. The crystallographic data were obtained from the COD database and the inputs were prepared by CIF2CELL code. The results were visualized using Xmgrace and VESTA software.

Study of electrodeposited zinc selenide (ZnSe) nanostructure thin films for solar cell applications

Electrodeposition approach was used to grow the ZnSe nanostructure on indium doped tin oxide (ITO) layered glass substrate. Due to low cost and high degree of absorption, binary semiconductors made from chalcogens such as CdSe, ZnO, ZnS and ZnSe provide significant features in photovoltaic and photoelectrochemical cells. The structural and morphological properties of deposited nanostructures were examined by XRD and SEM. X-ray diffraction analysis informed about cubic structure with a preferred orientation and the calculated crystal size was approximately 75 nm. The optical properties were examined by UV–visible absorbance spectra and optical band gap was measured using Tauc plot. The deposited ZnSe nanostructure has direct band gap ∼2.52 eV at room temperature which was less than 2.82 eV which is the band gap of bulk ZnSe. Investigations also focused on additional qualities like excellent optical transmission, low electrical resistance, and good photosensitivity. Because of the presence of defect states in the deposited nanostructure, the band gap energy is smaller than that of bulk material. The current-voltage characteristics were measured in dark mode and under illumination of normal tungsten filament light and LED. There was notable change in the current for both normal light and LED in comparison to dark mode. The findings of all the characterization methodologies suggested that for the production of solar cells low cost ZnSe may be used as an alternative environment friendly Cd-free window layer.

Enhanced photocatalytic degradation of cationic dye using Cu-doped ZnSe

The persistence of organic contaminants in an aqueous system adversely influences the ecosystems. To alleviate this ruinous issue, Cu doped ZnSe nanostructure is investigated for its catalytic performance assisted with hydrogen peroxide (H2O2) where cationic Methylene Blue (MB) is employed as a model contaminant. The Cu-doped ZnSe nanocatalysts are synthesized by a solvothermal approach and are characterized by XRD, FTIR, XPS, FE-SEM-EDX, BET, UV-VIS Spectroscopy, and PL. Enhancement in Cu doping improves the degradation performance of H2O2 assisted MB degradation, where with 5% of Cu-doping achieved 95.69% and 15% of Cu doping attains 98.09% of MB degradation across 180 min under visible light illumination. The proficient exculsion of MB dye by using Cu-doped ZnSe is attributed to Cu dopant, which decreases ZnSe bandgap and serves as an electron trapping center that inhibits the recombination of charge carriers. Among all, 15% Cu-doped ZnSe when assisted with H2O2 exhibits the highest degradation efficiency under visible light illumination is a repercussion to the synergetic effect of high surface area, tunable bandgap, and enhanced charge carriers separation owning to electron scavenging effects of H2O2. Thus, offering a promising strategy in fulfilling the upcoming environmental issues concerned with the removal of organic dyes from water reservoirs.

First-principles study of the structural, electronic and optical properties of Zn1-xHgxSe (x = 0, 0.25, 0.50, 0.75, 1)

The structural, electronic and optical properties of Zn1-xHgxSe alloys with different Hg concentrations (x = 0, 0.25, 0.50, 0.75, 1) are studied through first-principles calculations. The stability of three Zn1-xHgxSe ternary alloys is proved by calculating phonon spectrum. It is found that the SOC effect on the band gap is less than 0.2 eV. In addition, the HSE06 functional underestimates the band gap of ZnSe, so the PBE0 functional is employed to calculate the electronic and optical properties of Zn1-xHgxSe alloys. The tunable band gap can be realized by Hg doping from 2.5 to 0 eV Zn0.75Hg0.25Se and Zn0.50Hg0.50Se have suitable band gaps (1.0–1.8 eV) for solar cells. Zn0.50Hg0.50Se shows wider and higher absorption coefficient than that of Zn0.75Hg0.25Se in the visible light range.

Fabrication of highly efficient pure blue-emitting electroluminescent devices using ZnSe/ZnSexS1-x/ZnS QDs

Since electroluminescent (EL) quantum dots (QDs) are considered a key component of the next-generation display, and large-scale production of environment-friendly QDs is required for their wide use in commercial displays. Therefore, several studies on non-cadmium QDs, such as indium phosphide (InP) QDs in the III-V category, graphene QDs, and copper indium sulfide (CuInS2) or silver indium sulfide (AgInS2) QDs in the I-III-VI2 category, have been conducted owing to their non-toxicity and good optical properties. Subsequently, significant results have been reported for green and red colors. However, for synthesis of blue QDs, pure blue emission in the range of 440-460 nm has been achieved with few materials. Among them, zinc selenide (ZnSe) is a promising candidate for synthesizing blue QDs. However, owing to the wide band gap (2.7 eV) of ZnSe, highly effective QDs were attained in the violet region (420-440 nm). Here, for the first time, we have synthesized ZnSe/ZnSexS1-x/ZnS QDs emitting at a wavelength of 444 nm with high photoluminescence quantum yield (PLQY) of 77.2%. Also, full width at half maximum (FWHM) of 23.3 nm ensured its excellent color purity. Use of a gradient intermediate shell of ZnSeS in the original ZnSe/ZnS QDs was the key factor behind this achievement. The intermediate gradient shell of ZnSeS around the core delocalizes the electrons, weakening the quantum confinement effect (QCE), hence rendering the emission color of the QDs tunable from violet to blue by manipulating the ratio of selenium (Se) and sulfur (S) in the composites. A blue emission peak centered at 452 nm was observed for the quantum dot light-emitting diodes (QD-LEDs) fabricated using the above-mentioned QDs, and an external quantum efficiency (EQE) of 5.32%, current efficiency of 1.51 cd/A, and power efficiency of 0.74 lm/W were reported. Furthermore, our fabricated device exhibited a maximum brightness of 3,754 cd/m2 and a half operational time (LT50) with 100 cd/m2 initial luminance of 1.27 h, which are the highest values of these parameters to be reported till date for a blue QD-LED fabricated using ZnSe core based QDs in pure blue region.

Effect of Heat Treatment on Electrodeposited ZnSe on Vertically Aligned ZnO Nanorods for Photoelectrochemical Cell

Following successful growth of zinc oxide (ZnO) nanorods, a layer of zinc selenide (ZnSe) was electrodeposited onto the nanorods to further enhance its conversion efficiency in the photoelectrochemical (PEC) cell. The electrodeposited ZnSe layer onto the ZnO nanorods was subjected to heat treatment at 200, 250 and 300°C. The prepared films were characterized by X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), and ultraviolet-visible spectroscopy (UV-Vis) to investigate the structural, morphological and compositional characteristics. Additionally, PEC conversion generated by the prepared thin films were tested with photocurrent measurements under calibrated visible illumination from a halogen lamp. Based on FESEM analysis, the thickness of ZnO thin film increased with temperature. However, the diameters of the ZnO nanorods were found to be in a decreasing trend upon heat treatment at higher temperature. The electrodeposited ZnSe layer at the potential of -0.7 V for 60 seconds (calcined at 200°C) possessed crystallite size of 20.1 nm. According to UV-Vis analysis, band gap energy measured was 2.8 eV, which is very close to standard ZnSe band gap value (2.7 eV). Additional layer of ZnSe electrodeposited enhanced thin film performance in terms of current density as much as 37.4% while having high photocurrent density of 0.2671 mAcm-2.

Surface and intrinsic contributions to extinction properties of ZnSe quantum dots

This work studies extinction properties of ZnSe quantum dots terminated with either Se-surface or Zn-surface (Se-ZnSe or Zn-ZnSe QDs). In addition to commonly observed photoluminescence quenching by anionic surface sites, Se-ZnSe QDs are found to show drastic signatures of Se-surface states in their UV-visible (Vis) absorption spectra. Similar to most QDs reported in literature, monodisperse Zn-ZnSe QDs show sharp absorption features and blue-shifted yet steep absorption edge respect to the bulk bandgap. However, for monodisperse Se-ZnSe QDs, all absorption features are smeared and a low-energy tail is identified to extend to an energy window below the bulk ZnSe bandgap. Along increasing their size, a cyclic growth of ZnSe QDs switches their surface from Zn-terminated to Se-terminated ones, which confirms that the specific absorption signatures are reproducibly repeated between those of two types of the QDs. Though the extinction coefficients per unit of Se-ZnSe QDs are always larger than those of Zn-ZnSe QDs with the same size, both of them approach the same bulk limit. In addition to contribution of the lattice, extinction coefficients per nanocrystal of Zn-ZnSe QDs show an exponential term against their sizes, which is expected for quantum-confinement enhancement of electron-hole wavefunction overlapping. For Se-ZnSe QDs, there is the third term identified for their extinction coefficients per nanocrystal, which is proportional to the square of size of the QDs and consistent with surface contribution.

Impact of vacancy defects on optoelectronic and magnetic properties of Mn-doped ZnSe

Based on first principles calculations, we have investigated the electronic, magnetic and optical properties of Mn-doped ZnSe with and without vacancy defects. We find that the incorporation of Mn at Zn site changes the non-magnetic ground state of ZnSe to magnetic ground state with total magnetic moment 5 μB. From the investigation of magnetic coupling, it is found that the interaction between Mn spins in Mn-doped ZnSe is AFM which can be explained in term of super-exchange mechanism. The effect of vacancy defects such as Zn or Se vacancy on magnetic coupling between Mn spins were also analyzed and we found that Zn-vacancy promotes double exchange interaction which stabilizes the ferromagnetic state and room temperature ferromagnetism is expected while Se-vacancy doesn’t change magnetic ground state from AFM to FM states. The magnetic interactions in Mn-doped ZnSe system with and without Zn vacancy were explained using phenomenological band structure model. Moreover, optical absorptions for all systems were investigated at their stable magnetic states and we found that Mn doping causes the red shifted in absorption edge which is due to the spin forbidden d-d transitions (4T1-6A1) in Mn ions. The new peak in low energy range is related to the acceptor states introduced by Zn-vacancy in Mn-doped ZnSe system. The Se-vacancy generates peaks in visible region which is attributed to the donor states caused by Se-vacancy. Finally, the d-d transition (4T1-6A1) in FM and AFM coupled Mn ions were also studied and we found that the d-d transition peaks in AFM and FM coupled Mn ions are blue and red shifted respectively. Similarly, the blue and red shift in the energy bandgap of ZnSe are also observed in AFM and FM coupled Mn ions which support the agreement between the experimental and theoretical observations.

Pulsed Laser Annealing Effect on Optical and Structural Properties of ZnS/ZnSe Heterostructures

Studies of pulsed laser annealing (PLA) on semiconductor thin films were performed to examine changes of the optical and structural parameters due to the laser heat. Thin films of ZnS/ZnSe were deposited on quartz substrates at a pressure of 8.2*10-6 mbar using PVD technique. These thin films were annealed at different laser powers using CO2 pulsed laser. Transmission and reflection spectra were recorded before and after the annealing process. A decrease in the transmission and reflection spectra after annealing is observed. The absorption coefficient, refractive index, damping coefficient and dielectric constant were calculated before and after the annealing process. Changes in the optical parameters are found after the annealing process. The energy band gaps of ZnS and ZnSe have been determined. Upon annealing, an increase in the absorption coefficient is observed which is due to an improvement in the granular nanostructure of the ZnS/ZnSe thin films. XRD patterns of the prepared samples were obtained before and after the annealing procedure and revealed an enhancement in the crystallite structure upon annealing.

The manipulation of the physical properties of some typical zinc-blende semiconductors by the electric field

In this research, we regulate the band gaps of some typical zinc-blende semiconductors by applying an external electric field. The variation of the geometric structures and the band gaps of AlP, AlAs, AlSb, GaP, GaAs, ZnO, ZnSe and ZnTe have been studied. We also calculated the stability, density of states, band structures and the charge distribution by the first-principles method based on density functional theory. Moreover, the giant Stark effect coefficients have also been analyzed in detail. From our results, we find that the magnitude and the direction of the electric field has a significant regulation effect on the band gaps and the electronic structures of AlP, AlAs, AlSb, GaP, GaAs, ZnO, ZnSe and ZnTe, which induces a phase transition from semiconductor to metal beyond a certain electric field. Therefore, we can regulate the physical properties of this type of semiconductors by tuning the magnitude and the direction of the electric field. This is very important for practical applications in nanoelectronic devices.

One-pot facile synthesis of the ZnO/ZnSe heterostructures for efficient photocatalytic degradation of azo dye

Environmental remediation using sunlight is one of the most promising and cost-effective approaches to mitigate environmental hazards significantly related to the industrial development. In the present work, we report the synthesis of ZnO/ZnSe heterostructure via one-pot hydrothermal approach for the photocatalytic degradation of diazo dye i.e. Congo red. XRD analysis verified the crystal structure, phase purity and successful synthesis of the ZnO/ZnSe heterostructure photocatalysts. Moreover, the morphology and elemental composition of the photocatalysts were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron dispersive X-ray spectroscopy (EDX), respectively. The alignment of energy levels for the synthesized heterostructured photocatalysts was also drawn while using UV-visible diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS). Finally, the as-synthesized heterostructures were employed as efficient photocatalysts for the degradation of Congo red under the illumination of UV-visible light. Our results indicated that ZnO/ZnSe heterostructure photocatalysts with maximum ZnSe content can efficiently degrade the dye up to 91% which might be attributed to the effective charge separation as extended solar absorption due to narrow bandgap of ZnSe.

Electronic Properties of Exciton in Mg Based II–VI Wide Band Gap Semiconducting Quantum Dots

Electronic properties of exciton in Mg based ZnS, ZnSe and ZnTe wide band gap semiconductor cylindrical quantum dots are investigated taking into consideration of geometrical confinement effect. The confinement potentials for various concentrations of Mg alloy content in Zn1–xMgxS/MgS, Zn1–xMgxSe/MgSe and Zn1–xMgxTe/MgTe quantum dots are studied and the constant barrier height is maintained for the Mg content in all the three heterostructures (Zn0.9Mg0.1S/MgS, Zn0.25Mg0.75Se/MgSe and Zn0.09Mg0.91Te/MgTe) to obtain the exciton binding energies and the optical transition energies. The results show that the band gap increases nonlinearly with the increase of composition of Mg alloy content in the taken materials due to the positive band gap bowing parameters and the exciton binding energies in Zn0.9Mg0.1S/MgS quantum dot are found to be more than the other two dots taken for studies. Our results will be helpful for some potential applications in full colour display devices and optical data storage devices.

Construction of coaxial ZnSe/ZnO p–n junctions and their photovoltaic applications

Coaxial ZnSe/ZnO nanostructures were fabricated by coating a ZnO thin film on the surface of presynthesized p-type ZnSe 1D nanostructures by a sputtering method. Owing to the n-type behavior of ZnO resulting from intrinsic defects, coaxial ZnSe/ZnO p–n junctions were realized and showed a pronounced rectifying behavior. Photovoltaic devices based on the coaxial ZnSe/ZnO p–n junction showed a power conversion efficiency of 1.24% and a large open-circuit voltage of 0.87 V under UV light. The large bandgaps of ZnSe and ZnO and the high quality of the ZnSe/ZnO interface were considered to be related to the high performance of the devices.

Co-doping of Ag into Mn:ZnSe Quantum Dots: Giving Optical Filtering effect with Improved Monochromaticity.

In optics, when polychromatic light is filtered by an optical filter, the monochromaticity of the light can be improved. In this work, we reported that Ag dopant atoms could be used as an optical filter for nanosized Mn:ZnSe quantum dots (QDs). If no Ag doping, aqueous Mn:ZnSe QDs have low monochromaticity due to coexisting of strong ZnSe band gap emission, ZnSe trap emission, and Mn dopant emission. After doping of Ag into QDs, ZnSe band gap and ZnSe trap emissions can be filtered, leaving only Mn dopant emission with improved monochromaticity. The mechanism for the optical filtering effect of Ag was investigated. The results indicate that the doping of Ag will introduce a new faster deactivation process from ZnSe conduction band to Ag energy level, leading to less electrons deactived via ZnSe band gap emission and ZnSe trap emission. As a result, only Mn dopant emission is left.

Electronic and chemical structure of an organic light emitter embedded in an inorganic wide-bandgap semiconductor: Photoelectron spectroscopy of layered and composite structures of Ir(BPA) and ZnSe

Luminescent organic phases embedded in conductive inorganic matrices are proposed for hybrid organic-inorganic light-emitting diodes. In this configuration, the organic dye acts as the radiative recombination site for charge carriers injected into the inorganic matrix. Our investigation is aimed at finding a material combination where the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the organic dye are situated in between the valence and conduction bands of the inorganic matrix in order to promote electron and hole transfer from the matrix to the dye. Bilayer and composite thin films of zinc selenide (ZnSe) and a red iridium complex (Ir(BPA)) organic light emitter were prepared in situ via UHV thermal evaporation technique. The electronic and atomic structures were studied applying X-ray and ultraviolet photoelectron spectroscopies. The measured energy band alignments for the ZnSe/Ir(BPA) bilayer and ZnSe+Ir(BPA) composite reveal that the HOMO and LUMO of the organic dye are positioned in the ZnSe bandgap. For the initial steps of ZnSe deposition on a dye film to form Ir(BPA)/ZnSe bilayers, zinc atoms intercalate into the dye film leaving behind an excess of selenium at the interface that partly reacts with dye molecules. Photoelectron spectroscopy of the composites shows the same species suggesting a similar mechanism. This mechanism leads to composite films with increased content of amorphous phases in the inorganic matrix, thereby affecting its conductivity, as well as to the presence of nonradiative recombination sites provided by the intercalated Zn atoms.

Caution for monitoring the surface modification of dually emitted ZnSe quantum dots by time-resolved photoluminescence

This work wants to give a caution for monitoring the surface modification of dually emitted ZnSe quantum dots (QDs) by using time-resolved photoluminescence (PL). Aqueous ZnSe QDs have two emission bands: namely ZnSe band gap emission centered at 395 nm and ZnSe trap emission centered at 470 nm. By fitting the measured PL spectra by two peaks, serious overlapping of two emission bands can be found in the range of 360–430 nm. As a result, the measured PL lifetimes at 395 nm (the peak position of ZnSe band gap emission) is just an apparent value, composing of both ZnSe band emission (contribution proportion about 80%) and ZnSe trap emission (contribution proportion about 20%). Due to the much smaller PL lifetime of ZnSe band gap emission (less than 20 ns) than that of ZnSe trap emission (about 50–70 ns), the elevated contribution proportion of ZnSe band gap emission at improved QD surface modification will lead to the decreased average PL lifetime at 395 nm. This result is completely opposite to the traditional result where improved QD surface modification leads to increased PL lifetimes on the basis of single emitted QDs. Hence, when time-resolved PL is used for monitoring the surface modification of dually emitted QDs, the emission bands overlapping should be taken into consideration with caution.

Photoinduced charge redistribution and its influence on excitonic states in Zn(Cd)Se/ZnMgSSe/GaAs quantum-well heterostructures

The photoinduced charge redistribution in Zn(Cd)Se/ZnMgSSe/GaAs quantum-well heterostructures under different conditions of optical excitation has been investigated using scanning probe microscopy and optical spectroscopy in the temperature range from 5 to 300 K. Excitation of the samples by radiation with a photon energy greater than the band gap of Zn(Cd)Se leads to the accumulation of electrons in quantum wells, which is detected using scanning spreading resistance microscopy. For moderate excitation densities (up to 25 W/cm2) and at temperatures ranging from 80 to 100 K, the density of a quasi-two-dimensional electron gas formed in quantum wells is several orders of magnitude higher than the density of electron-hole pairs generated by the excitation radiation. The excess electron concentration in the quantum well leads to a broadening of the exciton resonances and to an increase in the relative intensity of the donor-bound exciton emission line and also determines the increase in the luminescence quantum yield with increasing excitation intensity. An additional illumination with a photon energy less than the band gap of Zn(Cd)Se decreases the concentration of excess electrons in quantum wells. The influence of the additional illumination is observed at a temperature of approximately 100 K and almost completely suppressed at 5 K. The obtained results are explained in terms of the formation of a potential barrier for electrons at the ZnMgSSe/GaAs interface and by the specific features of recombination processes in the electron-hole system containing impurity centers with different charge states.

Broadband down-conversion for silicon solar cell by ZnSe/phosphor heterostructure.

Down-conversion is a feasible way to improve conversion efficiency of silicon solar cell. However, the width of excitation band for down-converter based on trivalent lanthanide ions is still not satisfying. Here, we designed and fabricated a heterostructural down-converter composed of Y₂O₃: [(Tb³⁺-Yb³⁺), Li⁺] quantum cutting phosphor and ZnSe. The ZnSe phase was used to absorb the incident light with energy larger than its bandgap, and transfer the energy to Tb³⁺-Yb³⁺ quantum cutting couple. Short-wavelength incident light was finally converted into a strong Yb³⁺ emission at about 1000 nm, locating at the maximal spectral response of silicon solar cell. The excitation band of the down-conversion covers a wide region of 250-550 nm. Benefiting from the energy match between ZnSe bandgap and ⁷F₆→⁵D₄ absorption of Tb³⁺ ions, the bandwidth of down-conversion is almost maximized.