ZnTe Thin Films Research Articles

Zinc telluride material properties for solar cell application: Absorber layer

Over recent years, Zinc Telluride (ZnTe) has garnered significant interest from researches. This p-type semiconductors boasts a broad band gap, rendering it valuable in various optoelectronic uses like solar cells, LEDs, and laser displays. Given the growing interest in environmentally friendly energy alternatives, exploring the potential of nano-scale semiconducting materials for solar cells is particularly intriguing. ZnTe stands out due to its direct, wide, and adjustable optical band gap, along with its simple doping process, positioning it as a promising candidate for applications in photochemistry. This study aims to consolidate the research conducted by multiple investigators concerning the optical characteristics and electrical attributes of ZnTe thin films. The primary focus is on understanding how deposition methods and doping impacts these properties. The investigation reveals that the diverse doping techniques employed by different researchers have been extensively examined, demonstrating a positive influence of doping on these properties as well. Following the creation of solar cells based on ZnTe, they have emerged as viable and competitive substitutes for silicon solar cells, thanks to their economical nature and stable performance. As a result, there has been notable focus on advancing ZnTe thin film solar cell technology due to their promising capacity to serve as sustainable energy generators.

Preparation and optimization of all-inorganic CdSe/ZnTe solar cells

Cadmium selenide (CdSe) demonstrates high potential as a top cell material for Si-based tandem applications. However, obtaining high-quality CdSe thin films presents a significant challenge. Additionally, the intrinsic n-type conduction of CdSe desires a well-matched wide bandgap p-type partner to form a p-n junction for efficient photovoltaic applications. Herein, the vapor transport deposition method is employed to fabricate CdSe thin films with large grain sizes (∼2 μm), high crystallinity (with (002) preferred orientation), and strong band-edge photoluminescence. Moreover, zinc telluride (ZnTe), a II-VI group compound showing a low lattice mismatch of <0.7 % with CdSe, is explored as a p-type layer to construct solar cells. The properties of ZnTe thin film have been extensively studied and analyzed. By studying the annealing temperature (300 °C–550 °C), we obtained ZnTe film with a wide bandgap of 2.17 eV and conductivity of 1.4 × 10−5 S cm−1. To further enhance the carrier density of the ZnTe film, we employ a Cu doping strategy involving treatment with varying concentrations of CuBr solution (0 mg mL−1, 1 mg mL−1, 2.5 mg mL−1, 10 mg mL−1). Ultimately, a power conversion efficiency (PCE) of 2.03 % is achieved in CdSe/ZnTe solar cells. This is a primary exploration of all-inorganic CdSe/ZnTe solar cells, proving their potential for photovoltaic applications. Further optimization is deserved to achieve higher PCE.

Effect of phonon anharmonicity on thermal conductivity of ZnTe Thin films

The ZnTe thin film is a potential material for optoelectronic devices in extreme temperature and radiation environments. In this report, the thermal conductivity of ZnTe films is measured non-invasively using the micro-Raman method and correlated with the phonon anharmonic effect. The evolution of crystalline ZnTe thin films from Te/ZnO bilayer by thermal annealing at 450 ∘C has been observed above the melting point of Te, which is confirmed from x-ray diffraction and high-resolution transmission electron microscopy. The ZnTe thin films illustrate three longitudinal phonon modes with higher harmonics of nLO (n = 3) at room temperature. Temperature-dependent Raman spectra in the range of 93–303 K are used to analyze the phonon anharmonicity from Raman shift, FWHM, and Phonon lifetime of the thin films. The Balkanski model is used to fit the anharmonicity-induced phonon frequency shift of nLO modes as a function of temperature, taking into account three- and four-phonon interactions. The intensity ratio of the I 2LO /I 1LO and I 3LO /I 2LO provide information about the electron-phonon coupling strength, which is influenced by the anharmonic effect. The laser power-dependent Raman spectra are used to determine the thermal conductivity of the ZnTe films, which is found to be approximately 9.68 Wm−1K−1, remains relatively constant for all nLO modes, indicating that multi-phonon scattering process. The correlation between thermal conductivity and phonon anharmonicity can pave the way for understanding the phonon scattering process in ZnTe thin films for high-performance optoelectronic device applications in harsh conditions.

Improved phosphorus doping in ZnTe by molecular beam epitaxy under alternating source supply

Phosphorus (P) doping in ZnTe grown by molecular beam epitaxy (MBE) under alternating source supply method was investigated to achieve p-type P-doped ZnTe (ZnTe:P) thin films using InP as a P dopant source, and the result was compared with those grown under a simultaneous MBE growth where the source beams were supplied simultaneously. As a result, P concentration in ZnTe thin films was found to increase with increasing the InP flux, and high P concentration up to 6.6 × 1019 cm−3 was confirmed by secondary ion mass spectroscopy (SIMS) analyses. However, In incorporation was also observed in the ZnTe:P thin films, despite that the detected In concentration by SIMS was more than one order of magnitude lower than the P concentration and almost two order of magnitude lower than those grown by the simultaneous MBE. Photoluminescence measurement of ZnTe:P thin film grown under alternating source supply showed a P-related acceptor bound exciton (Ia) peak at 2.37 eV, and the intensity of Ia emission increased after the annealing treatment, indicating the activation of P acceptor. The annealing also decreases the resistivity of the film. The results clearly indicate that the alternating source supply growth is effective to obtain ZnTe:P thin films with better P doping properties.

Numerical investigation on the role of ZnTe back surface layer in an efficient CuInS2 thin film solar cell

This paper presents the modeling and numerical inspection of an efficient CuInS2-based n-CdS/p-CuInS2/p+-ZnTe thin film solar cell applying the SCAPS-1D simulator. The various parameters used in the simulation have been obtained from existing literature. The optimization of the device has considered the width, doping concentration, and defect density of individual layer. The optimized standalone CuInS2 device shows an efficiency of 16.83%. Addition of ZnTe in the device gives an impressive efficiency of approximately 28.67%, having a current density, JSC of 25.58 mA cm−2, a VOC of 1.25 V, and an FF of 89.12%. The superior VOC is a result of the increased built-in potential formed at the hetero-interfaces of the device and the decrease in surface recombination velocity by back surface field effect in the ZnTe layer. The highest JSC is ascribed to the enhancement of the absorption of vis-infrared photons by back surface field (BSF) effect in the ZnTe layer. These findings demonstrate the potential for manufacturing high efficiency CuInS2-based thin film solar cells in the future.

Fabrication and optical characterization of zinc telluride thin films using electrodeposition technique

A well adherent thin film of Zinc Telluride (ZnTe) has been deposited on Flourine doped Tin oxide glass substrates from acidic baths containing Zinc heptahydrate and Tellurium dioxide. Films of different thicknesses with their molar concentrations were obtained. A mini Schimadzu UV-VIS Spectrophotometer was used to determine the optical absorbance of the films over the wavelength range of 300-900nm at room temperature. There is a decrease in absorbance as the molar concentrations of the precursors increases; while transmittance and energy band gap shown an increase. The band gap values obtained varied between 2.10eV and 2.7eV, for as deposited films. Also, photoelectrochemical cell (PEC) measurement reveals that ZnTe thin films exhibit p-type conductivity.

Growth and Photoelectrochemical Characterization of Epitaxial ZnTe Photocathodes for Carbon Dioxide Reduction

Harnessing solar energy to drive photocatalytic carbon dioxide reduction reactions (CO2RR) provides an appealing pathway to generate hydrocarbon and oxygenated fuels without an external power source. Zinc telluride (ZnTe) is a II-VI semiconductor which has been identified as a promising photocathode material due to its suitable band gap alignments to CO2 reduction reaction potentials, chemical stability, and strong p-type character. Using molecular beam epitaxy (MBE), single crystal and epitaxial layers are synthesized to gain a deeper understanding of fundamental charge transport and reactivity mechanisms between the single crystal ZnTe thin film and the CO2-saturated electrolyte. These findings are of fundamental interest and are also critical to the design of efficient tandem solar fuels generators for unassisted photoelectrochemical CO2R. Epitaxy allows for highly controlled doping of the thin films over a large range of carrier concentrations. This work focuses largely on the synthesis and characterization of nitrogen doped p-type ZnTe via MBE. Films grown in the temperature range of 340–360ºC on GaAs of (100) orientation with a 200 nm undoped ZnTe buffer layer and a 100 nm doped ZnTe layer have been characterized by RHEED, XRD, AFM, and Hall effect measurements. Doping concentrations between 1020 cm-3 and 1018 cm-3 have been achieved. Dark current-voltage measurements have been used to indicate stability of the electrode in aqueous conditions in less than -0.5 V vs RHE. Future work will include further investigations into carrier dynamics via transient absorption spectroscopy and continual development of a tandem, ZnTe-based photocathode.

Carrier-mediated ferromagnetism in Mn(II)-doped ZnTe thin films and their optical properties: A first-principles study

We have investigated the opto-electronic and magnetic properties of Mn(II)-doped ZnTe thin films by employing Density Functional Theory (DFT). In the absence of additional carriers, spin-up Mn-ta levels are fully occupied, leading to a super-exchange mechanism. The effect of additional p-type doping on the ferromagnetism is studied by considering the addition of hole carriers, Zn vacancies, and C co-doping, and we found that in all cases, coupling of hole carriers with the spin-up Mn-states causes the stability of the ferromagnetism in the Mn(II)-doped ZnTe thin films. We discovered through the optical study that Mn(II) doping at the Zn site widens ZnTe's bandgap and produces spin-forbidden d-d transition peaks on the low energy side of the bandgap. The p-type defects in Mn(II)-doped films produce absorption peaks in the infrared region and improve the absorption efficiency. In addition, the optical bandgap and spin-forbidden d-d transition of Mn(II) to different modes of spin-spin interactions were correlated, and we found a red shift of d-d intra-band transition peaks as well as an optical bandgap in the FM-coupled Mn(II) ions system and a blue shift in the AFM coupled ions system, supporting the experimental observations.

Fabrication and investigation of zinc telluride thin films

Zinc Telluride ZnTe alloys and thin film have been fabricated and deposited on glass substrates by thermal evaporation method which may be a suitable window layer of zinc telluride with different annealing temperatures (373 and473) K for 60 minutes in vacuum. Deposited thin films with thickness 100 nm was characteristic by using X-ray diffraction XRD to know structures, Atomic Force Microscopy (AFM) to evaluate surface topology, morphology. It was found out that the vacuum annealing improves on thin ZnTe films structure and surface morphology. Structural analysis reveals that ZnTe films have zinc blende structure of cubic phase with (111) preferred reflection and grain size is enhanced from 8.6 to 16.7 nm with annealing. Optical properties where optical bandgap energy values slightly decreased (2.3-2.2) eV as the annealing temperatures.

Validation of ZnTe as back surface field layer for CdTe solar cells: A combined experimental and theoretical study

An excellent back contact layer is one of the key requirements for thin-film solar cells with a high energy conversion efficiency. For a highly resistive compound such as CdTe thin-film, fabrication of contact with low electrical contact resistance along with a high electron affinity is very difficult. Herein, we have thoroughly investigated the possibility of using ZnTe as a back contact layer for CdTe-based solar cells through combined experimental and first-principle studies. CdTe and ZnTe thin films were deposited on the glass substrate. Detailed structural, morphological, elemental, electrical, and optical properties are investigated through different experimental techniques. Then p-ZnTe/n-CdTe heterojunction was fabricated, and junction properties were studied. Precise electronic band-structures were obtained for CdTe, ZnTe, and CeTe/ZnTe heterojunctions. The interface properties, band edge position, and band alignments were estimated by using the HSE06 hybrid functional method. Detailed theoretical results substantiate our experimental findings.

Growth of phosphorus-doped ZnTe thin films by molecular beam epitaxy using InP as the dopant source

P-doped ZnTe thin films were grown by MBE on ZnTe (100) substrates using InP as the P source under various InP fluxes. Secondary ion mass spectroscopy (SIMS) analyses showed that the P concentration in ZnTe thin films increased with increasing InP flux, although In atoms were also incorporated in the films. To suppress In incorporation, the outlet of the InP cell was modified by mounting a cap and a plate with small holes. As a result, In incorporation was significantly suppressed, resulting in an In concentration three orders of magnitude lower, as confirmed by SIMS, although the P concentration also decreased by almost one order of magnitude compared with the case without a cap. An acceptor-bound exciton (Ia) peak was observed at around 2.36 eV in the P-doped ZnTe thin film grown with a cap, and the Ia intensity increased after annealing, indicating the activation of P acceptors.

Resulting Effect of the p-Type of ZnTe: Cu Thin Films of the Intermediate Layer in Heterojunction Solar Cells: Structural, Optical, and Electrical Characteristics.

The microstructural, electrical, and optical properties of Cu-doped and undoped ZnTe thin films grown on glass substrates are covered in this article. To determine the chemical makeup of these materials, both energy-dispersive X-ray (EDAX) spectroscopy and X-ray photoelectron spectroscopy were employed. The cubic zinc-blende crystal structure of ZnTe and Cu-doped ZnTe films was discovered using X-ray diffraction crystallography. According to these microstructural studies, the average crystallite size increased as the amount of Cu doping increased, whereas the microstrain decreased as the crystallinity increased; hence, defects were minimized. The Swanepoel method was used to compute the refractive index, and it was found that the refractive index rises as the Cu doping levels rises. The optical band gap energy was observed to decrease from 2.225 eV to 1.941 eV as the Cu content rose from 0% to 8%, and then slightly increase to 1.965 eV at a Cu concentration of 10%. The Burstein-Moss effect may be connected to this observation. The larger grain size, which lessens the dispersion of the grain boundary, was thought to be the cause of the observed increase in the dc electrical conductivity with an increase in Cu doping. In structured undoped and Cu-doped ZnTe films, there were two carrier transport conduction mechanisms that could be seen. According to the Hall Effect measurements, all the grown films exhibited a p-type conduction behavior. In addition, the findings demonstrated that as the Cu doping level rises, the carrier concentration and the Hall mobility similarly rise, reaching an ideal Cu concentration of 8 at.%, which is due to the fact that the grain size decreases grain boundary scattering. Furthermore, we examined the impact of the ZnTe and ZnTe:Cu (at Cu 8 at.%) layers on the efficiency of the CdS/CdTe solar cells.

Effect of deposition temperature on structural, morphological and optical properties of ZnTe thin films

Effect of deposition temperature on structural, morphological and optical properties of ZnTe thin films

An evolution to Cu concentration on ZnTe thin films: functionality as interface layer to CdTe solar cells

An evolution to Cu concentration on ZnTe thin films: functionality as interface layer to CdTe solar cells

Undoped p-type ZnTe thin film and thin film transistor channel performance

Undoped p-type ZnTe thin film and thin film transistor channel performance

Study of Optical and Electrical Properties of RF-Sputtered ZnSe/ZnTe Heterojunctions for Sensing Applications

Cadmium (Cd)-free photodiodes based on n-type Zinc Selenide/p-type Zinc Telluride (n-ZnSe/p-ZnTe) heterojunctions were prepared by Radio Frequency-Magnetron Sputtering (RF-MS) technique, and their detailed optical and electrical characterization was performed. Onto an optical glass substrate, 100 nm gold (Au) thin film was deposited by Thermal Vacuum Evaporation (TVE) representing the back-contact, followed by the successive RF-MS deposition of ZnTe, ZnSe, Zinc Oxide (ZnO) and Indium Tin Oxide (ITO) thin films, finally resulting in the Au/ZnTe/ZnSe/ZnO/ITO sub-micrometric “substrate”-type configuration. Next, the optical characterization by Ultraviolet-Visible (UV-VIS) spectroscopy was performed on the component thin films, and their optical band gap values were determined. The electrical measurements in the dark and under illumination at different light intensities were subsequently performed. The Current–Voltage (I–V) characteristics in the dark are nonlinear with a relatively high asymmetry, following the modified Shockley–Read equation. From their analysis, the series resistance, shunt resistance, the ideality factor and saturation current were determined with high accuracy. It is worth noting that the action spectrum of the structure is shifted to short wavelengths. A sensibility test for the 420–500 nm range was performed while changing the intensity of the incident light from 100 mW/cm2 down to 10 mW/cm2 and measuring the photocurrent. The obtained results provided sufficient information to consider the present sub-micrometric photodiodes based on n-ZnSe/p-ZnTe heterojunctions to be more suitable for the UV domain, demonstrating their potential for integration within UV photodetectors relying on environmentally-friendly materials.

الخصائص التركيبية والكهربائية والتحسسية لأغشية ZnTe الرقيقة المشوبة بالـ Cd والمحضرة بطريقة التبخير الحراري

This study concentrates on the examination of the functional, electrical, and sensing qualities of ZnTe thin films that were prepared by the thermal evaporation method, with a thickness of 300 nm deposited on glass bases prior to annealing at a temperature of (350ºC). The influence of doping with cadmium (7%) on the structural, electrical, and sensing properties of dopant films was also investigated. The results of XRD showed that the pure and doped films were polycrystalline and cubic. According to the findings of the electrical properties of this study, the specific resistance decreases with increasing temperature. It was found that the sensitivity of ZnTe films rises upon doping and annealing, so the sensitivity was calculated.

Copper-related defects in ZnTe thin films grown by the close space sublimation method

Low-temperature photoluminescence (PL) is used to study defects evolution via immersion technique and annealing in vacuum of ZnTe thin films. In this paper we studied how copper doping from solutions of different molar concentrations affects PL of ZnTe thin films grown by close space sublimation (CSS) method. Undoped ZnTe thin films showed PL emission in the (520-680) nm wavelength region. The incorporation of copper in ZnTe produce a number of broad emission bands that correspond to an electron transition from the conduction band to spin-orbit states of the localized level of Cu2+ ions. All the studied samples had variable concentrations of oxygen and the possibility of the formation of auxiliary oxides is discussed.

Morphological, optical, and electrical properties of RF-sputtered zinc telluride thin films for electronic and optoelectronic applications

Zinc telluride (ZnTe) thin films were deposited by radio-frequency magnetron sputtering (RF-MS) onto optical glass coated by a silver–copper (Ag:Cu) thin film representing the back-electrode, and they were subsequently electrically contacted with an aluminum (Al) layer acting as the top-electrode. The RF-MS procedure was carried out at 50 W in argon (Ar) gas atmosphere kept at 2.5 × 10−3 mbar working pressure for 75 min at a substrate temperature of 220 °C kept constant during deposition. Morphological investigations by scanning electron microscopy allowed a first evaluation of the ZnTe film’s thickness. Optical characterization was then performed via absorption and transmission measurements in the spectral range between 300 and 1500 nm at room temperature. Subsequently, the thickness and bandgap energy of the ZnTe thin film were evaluated to be ∼508 nm and ∼2.13 eV, respectively. Moreover, they revealed high transmittance in infrared and near infrared regions of the electromagnetic spectrum. Then, the electrical measurements of Ag:Cu/ZnTe/Al “sandwich” structure (current–voltage characteristics) at six temperatures ranging from 303 to 354 K were performed, allowing the identification of the charge transport mechanisms through the structure along with their corresponding parameters. Based on the excellent optical and electrical properties, these ZnTe thin films show great potential as candidates for performant small-wavelength photodetectors.

Effect of thermal annealing on physical properties of Cu-doped ZnTe thin films: Functionality as interface layer

Achieving a high quality interface is of great importance in CdTe based solar cells, as it appreciably inhibits interfacial recombination and consequently improves the photovoltaic performance. The low carrier density of CdTe absorber contributes to formation of back contact Schottky barrier which acts as diode setup in opposition to the CdS/CdTe junction. To overcome this problem, the Copper doped Zinc Telluride (ZnTe:Cu) material is estimated to be a good nominee for such interface layer due to its high chemical immovability and appropriate band gap alignment with CdTe absorber. Hence, the present work demonstrates thermal annealing evolution to 200 nm thin resistive heating grown ZnTe:Cu 1 % films to find their feasibility as back/rear contact material in the CdTe based superstrate solar cell devices. The structural analysis revealed that as deposited and annealed ZnTe:Cu 1 % films have (103) preferred reflection with cubic phase and crystallite size is enhanced from 22 nm to 42 nm with annealing. The optical transmittance is varied with annealing and the direct optical energy band gap is found within the range of 2.10–2.74 eV. The pristine and annealed films showed ohmic behavior and the AFM images displayed hill like topographies. Smaller to larger size spherical shaped grains and non-uniform cylindrical shaped grains morphology is obtained in FESEM images whereas the EDS patterns confirmed successful deposition of ZnTe:Cu 1 % thin films. The obtained results signify that the 300 °C annealed ZnTe:Cu 1 % films might be considered as interface layer material for the fabrication of CdTe based solar cell devices. • Annealing induced properties of ZnTe:Cu interface layer are investigated for solar cells. • The ZnTe:Cu films showed crystal growth along (103) preferred orientation. • Optical band gap of ZnTe:Cu films is found in 2.10–2.74 eV range with annealing. • AFM images showed hill-like topographies and EDS patterns confirmed films deposition. • SEM images revealed spherical grains and I-V curves ensured ohmic nature.