ZnTe Phase Research Articles

Templet-free one-pot synthesis of Bi-doped ZnTe nanoflowers by cation exchange method for optoelectronic applications and antibacterial activity

The present report investigates the preparation of Bi-doped ZnTe (Bi:ZnTe) nanosheets (NS) with a variation in Bi contents for different optoelectronic applications and antibacterial responses. A flower-like Bi:ZnTe NS assemblies were synthesized by a cation exchange reaction, where the average thickness of the individual NS was found to be in the range of 20–30 nm. The average thickness of the NS gradually increases with an increase in the Bi concentration. The obtained NS shows high crystallinity properties with a hexagonal ZnTe phase. With the increase in the Bi concentration, there is no significant change in either crystallinity or the phase of the NS observed. The optical properties of the as-synthesized Bi:ZnTe NS were analyzed through the UV-Vis absorbance spectra, where a variation in the absorption edge with a change in the Bi content is apparent. The optical bandgap of the material gradually increases with an increment in the Bi concentration. The photoluminescence (PL) measurement was carried out to analyze the applicability of the NS for different optoelectronic applications. Broad PL spectra for different Bi:ZnTe NS are obtained in the 520–850 nm range, with the peak around 600 nm for 532 nm excitation. Due to the non-toxic nature of the constituent elements, the Bi:ZnTe NS is favorable for biological applications. The antibacterial activities of the Bi:ZnTe NS against two pathogenic bacteria are examined, where a good antibacterial response is observed.

Effect of substrate temperature on the deposited thin film CdZnTe transistor

CdZnTe thin film transistor (TFT) detector was deposited on Si/SiO 2 substrate by radio frequency (RF) magnetron sputtering technique. The influence of substrate temperature on the structure of CdZnTe film and the performance of CdZnTe TFT detector were studied. The sputtered CdZnTe films have a multiphase structure consisting of the CdZnTe phase, ZnTe phase and Te phase. (IDS–VDS) characteristics and photosensitivity of CdZnTe TFT detectors at different substrate temperature were reported. When the substrate temperature was 200 °C off-current in CdZnTe TFT detector achieved minimum value of 1.9×10−11 A, as well as a higher photosensitivity of 1.9×103 (obtained at VGS=28.5 V). The optimal condition for preparing CdZnTe TFT detector was the substrate temperature of 200 °C.

Shortening Nucleation Time to Enable Ultrafast Phase Transition in Zn1Sb7Te12 Pseudo-Binary Alloy.

Zn1Sb7Te12 thin films have been deposited by magnetron co-sputtering of ZnTe and Sb2Te3 targets. The microstructure, phase-change speed, optical cycling stability, and crystallization kinetics have been investigated during thermal annealing and laser irradiation. The thermal-annealed and laser-irradiated films give a clear evidence of the coexistence of trigonal Sb2Te3 and cubic ZnTe phases, which are homogeneously distributed in a single alloy as confirmed by advanced scanning transmission electron microscopy. The formation of both phases increases the initial nucleation sites, leading to the rapid phase-change speed in the Zn1Sb7Te12 film. The film has a minimum crystallization time of ∼3 ns at 70 mW with almost no incubation period for the formation of critical nuclei compared to Ge2Sb2Te5 and other Zn-based films. Moreover, the complete crystallization of Zn1Sb7Te12 thin films is achieved within 10 ns. The ultrafast two-dimensional nucleation and crystal growth speed in Zn1Sb7Te12 obtained from the laser-irradiated system is almost 7 times faster compared to that in Ge2Sb2Te5 film. Controlling the crystallization process through doping ZnTe into Sb2Te3 is thus promising for the development of high-speed optical switching technology.

Copper-induced recrystallization and interdiffusion of CdTe/ZnTe thin films

ZnTe is commonly employed as a buffer layer between CdTe and the metallization layer at the back contact of state-of-the-art CdTe solar cells. Here, the critical role of Cu in catalyzing recrystallization and interdiffusion between CdTe and ZnTe layers during back contact activation is presented. Several CdTe/ZnTe:Cu thin-film samples were prepared with varying levels of copper loading and annealed as a function of temperature and time. The samples were characterized by x-ray diffractometry, scanning electron microscopy, transmission electron microscopy, and energy dispersive x-ray spectroscopy. The results show that stress is present in the as-deposited bilayers and that negligible interdiffusion occurs in the absence of Cu. The presence of Cu facilitates rapid interdiffusion, predominantly via Cd migration into the ZnTe phase. Zn migration into CdTe is limited to areas around defects and grain boundaries. Ternary CdxZn1-xTe interlayers are formed, and the extent of alloy formation ranges from 0.08 < x < 0.5 throughout the whole ZnTe layer. The level of Cu loading controls the composition of the CuxTe clusters observed, while their size and migration is a function of annealing conditions.

Pressure influence on structural and optical behaviors of ZnTe thin films grown by PLD

In this work, ZnTe thin films were grown by pulsed laser deposition technique with the aim of study their structural and optical behaviors as function of deposition pressure and consider their potential application in optoelectronic devices. Hence, to obtain the stoichiometric ZnTe phase, the deposition temperature was considered as constant (286 °C) during growth process and deposition pressure was varied, as follow: 1, 20, 50, and 100 mTorr. After that, deposited films were characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and UV–Vis spectroscopy techniques. Characterization results reveals that deposited films correspond to stoichiometric, nanostructured, uniform and monophasic deposits of ZnTe with a strong preferential orientation in the (111) plane. It is noteworthy that thickness, grain size and crystal size of the films do not show a linear dependence on the range of deposition pressure. On the other hand, UV–Vis spectroscopy results indicate that band gap values of ZnTe films can be tuned in the range of 2.43–2.56 eV as function of deposition pressure. Lastly, it is consider that ZnTe thin films deposited at 20 mTorr present the best match between structural and optical characteristics for potential applications in development of optoelectronic devices.

Effect of vacuum annealing on structural and optical properties of nanocrystalline ZnTe thin films

In present study, dependence of structural and optical properties of nanocrystalline $$\hbox {Zn}_{40}\hbox {Te}_{60}$$ (ZnTe) thin films on vacuum thermal annealing has been investigated. ZnTe alloy was prepared by melt quenching technique and thermally evaporated on cleansed glass substrates to deposit thin films. These films were annealed in vacuum ( $$\sim 1\times 10^{-3}$$ mbar) for an hour at three different temperatures 100, 200 and 300 °C. X-ray diffraction results revealed the presence of cubic ZnTe phase in all the films along with some hexagonal Te phase. The crystallite size of ZnTe thin films improved on annealing with larger size at elevated temperatures (from 32 to 80 nm). Micro strain and dislocation density reduced owing to improvement in crystallinity after annealing. The IR transmittance increased with increase in annealing temperature. Field emission scanning electron microscopy images suggested the formation of smooth and uniform thin films with thickness of $$\sim$$ 480 nm. Optical properties revealed the decrease in transmittance and absorption edge shift due to crystallinity improvement on annealing. The optical band gap decreased from 1.37 to 0.91 eV on annealing. Experimental results show that thermal annealing has significant impact on structural and optical properties of ZnTe thin films.

Electrical properties of p-type ZnTe thin films by immersion in Cu solution

ZnTe thin films were deposited on SiO2 substrate by pulsed-laser deposition (PLD) at room temperature. The ZnTe films were immersed in different concentrations of Cu(NO3)2–3H2O solutions for 1min, then heated at 200 and 300°C, both temperatures for 10min in a N2 atmosphere. The X-ray diffraction (XRD) showed the hexagonal and orthorhombic ZnTe phases when the copper-doped films were heated at 200 and 300°C for 10min respectively. The films immersed in 15 and 60mg of Cu(NO3)2–H2O solutions had similar values of sheet resistance ~104Ω/□, resistivity ~10−1Ωcm, specific contact resistance ~10−4Ωcm2, and hall mobility 5cm2/Vs. Also, the copper-doped conditions were used to dope the source and drain bias to make a thin-film transistor of ZnTe (TFT) by photolithography.

Effects of Cu incorporation on physical properties of ZnTe thin films deposited by thermal evaporation

The present paper reports on a systematic study of the Cu doping effect on the optical, electrical and structural properties of ZnTe:Cu (Cu=0, 6, 8, and 10at%) thin films. Polycrystalline Cu-doped ZnTe thin films were deposited on glass substrates at room temperature by thermal evaporation. A detailed characterization of the Cu-doped ZnTe films were performed by X-ray diffraction (XRD), Spectrophotometry, Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy. XRD of the as-deposited Cu-doped ZnTe films belong to single-phase cubic structure of ZnTe with preferential orientation along (111) planes revealed minor effect of Cu content. The interference pattern in optical transmission spectra was analyzed to determine energy band gap, refractive index, extinction coefficient and thickness of the films. Wemple–DiDomenico and Tauc's relation were used for the determination and comparison of optical band gap values. The formation of ZnTe and Cu-doped ZnTe phase was confirmed by FT-IR. AC conductivity in a frequency range of 0–7MHz has been studied for investigation of the carriers hoping dynamics in the films. Raman spectra indicated merely typical longitudinal optical (LO) phonon mode of the cubic structure ZnTe thin film at 194cm−1 because the excitation energy is well above of the optical band-gap of the material and exhibited a blue-shift from 194 to 203cm−1 with Cu which could be associated to the substitution of Zn atom with Cu at the lattice sites.

Enhanced thermal stability and electrical behavior of Zn-doped Sb2Te films for phase change memory application

Zn-doped Sb2Te films are proposed to present the feasibility for phase-change memory application. Zn atoms are found to significantly increase crystallization temperature of Znx(Sb2Te)1−x films and be almost linearly with the wide range of Zn-doping concentration from x = 0 to 29.67 at.%. Crystalline resistances are enhanced by Zn-doping, while keeping the large amorphous/crystalline resistance ratio almost constant at ∼105. Especially, the Zn26.07(Sb2Te)73.93 and Zn29.67(Sb2Te)70.33 films exhibit a larger resistance change, faster crystallization speed, and better thermal stability due to the formation of amorphous Zn-Sb and Zn-Te phases as well as uniform distribution of Sb2Te crystalline grains.

Optical characteristics of wurtzite ZnTe thin films

The growth of wurtzite ZnTe thin films with thickness between 250 and 1000nm on borosilicate glass substrates by electron beam evaporation is reported. The formation of the wurtzite structure was confirmed using X-ray diffraction. The films showed diffraction peaks originating from the (110), (016) and (116) planes, indicating absence of any preferred orientation. The transmission of all the films was of the order of 80% in the near IR region. The refractive index of the wurtzite ZnTe phase increased with increase in thickness from 3.0 at 250nm to 4.2 for the 1000nm thickness film at a wavelength of 1800nm. The optical band gap of these films increased with thickness showing values of 0.85, 0.9 and 0.98eV at 250, 400 and 1000nm thickness, respectively. Chemical composition studies revealed that the films were mildly non-stoichiometric with excess Te. Comparison with the zinc blende structure of ZnTe shows that the wurtzite structure has a higher refractive index, lower band gap and lower charge carrier concentration.

ZnSb の熱電特性に対するテルル元素添加効果

n-type tellurium doped ZnSb was prepared by direct melting at 923 K after which it was quenched in water within an evacuated quartz ampoule. All the ingots were heat treated at 723 K for 100 h. The resultant samples were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA) and by measurement of their Seebeck and Hall coefficients. XRD and DTA indicated that the solubility limit of tellurium in ZnSb was less than 3 at%. The samples with 0, 1 and 3 at% tellurium were p-type while those with 1.90 and 2.06 at% tellurium were n-type. These results indicated that n-type ZnSb samples can be obtained by the proper doping of tellurium. Excess doping with tellurium resulted in precipitation of the ZnTe phase and a change in conduction from n- to p-type. The maximum power factor for the 2.06 at% tellurium doped n-type sample was found to be 0.84×10-3 Wm-1 K-2 at 573 K.

Ageing effect on mechanically alloyed ZnTe nanocrystals

Abstract After three years and three months keeping mechanically alloyed Zn 50 Te 50 sample and its annealed portion under ambient conditions, these samples were re-investigated using X-ray diffraction, differential scanning calorimetry and Raman spectroscopy measurements to verify changes on structural, thermal and optical properties with ageing. The X-ray diffraction patterns of the aged-as-milled samples showed that the zinc blende ZnTe phase fraction decreased and the minority trigonal tellurium and hexagonal ZnO phase fractions increased with ageing. Similar (but less intense) behavior was observed for the aged-annealed sample, except by the nucleation of the β -TeO 2 phase with ageing. Structural parameters, phase fractions, average crystallite sizes and microstrains of all crystalline phases were obtained from Rietveld analyses of the X-ray patterns for both aged samples. The DSC results corroborate the trigonal Te phase fraction variation with ageing found by XRD analyses. Raman measurements of aged ( as-milled and annealed ) samples showed an huge intensity decreasing and even disappearing of the zinc blende ZnTe phase signals with ageing, which cannot be explained by the zinc blende phase fraction variations observed by X-ray diffraction. Then, as trigonal Te features are predominant in the Raman spectra of aged samples (there are no evidences of Raman signals of the minority phases), one can suggests a kind of Te capping effect on the ZnTe, ZnO and TeO 2 nanocrystals.

Structural, electronic and optical properties of high pressure stable phases of ZnTe

Abstract We have performed full potential linear augmented plane wave calculations to investigate the pressure induced phase transition in ZnTe. Total energies of three phases (zinc-blende, cinnabar and Cmcm) are calculated using density functional theory formalism under generalized gradient approximation and Engel–Vosko generalized gradient approximation for the exchange correlation potential approximation. The pressure stability corresponding to zinc-blende, cinnabar and Cmcm phases of ZnTe are computed. We find that cinnabar phase could be formed as a metastable phase by releasing pressure from the high pressure Cmcm phase. The obtained structural, electronic and optical results are compared with previous calculations and available experimental data. Overall good agreement is found.

Effect of Tellurium Doping on the Thermoelectric Properties of ZnSb

N-type tellurium doped ZnSb was prepared by direct melting at 923 K after which it was quenched in water within an evacuated quartz ampoule. All the ingots were heat treated at 723 K for 100 h. The resultant samples were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA) and by measurement of their Seebeck and Hall coefficients. XRD and DTA indicated that the solubility limit of tellurium in ZnSb was less than 3 atomic%. The samples with 0, 1 and 3 atomic% tellurium were p-type while those with 1.90 and 2.06 atomic% tellurium were n-type. These results indicated that n-type ZnSb samples can be obtained by the proper doping of tellurium. Excess doping with tellurium resulted in precipitation of the ZnTe phase and a change in conduction from n- to p-type. The maximum power factor for the 2.06 atomic% tellurium doped n-type sample was found to be 0.84 ×10 -3 W m -1 K -2 at 573 K.

Development of electrodeposited ZnTe layers as window materials in ZnTe/CdTe/CdHgTe multi-layer solar cells

Zinc telluride (ZnTe) thin films have been deposited on glass/conducting glass substrates using a low-cost electrodeposition method. The resulting films have been characterized using various techniques in order to optimize growth parameters. X-ray diffraction (XRD) has been used to identify the phases present in the films. Photoelectrochemical (PEC) cell and optical absorption measurements have been performed to determine the electrical conductivity type, and the bandgap of the layers, respectively. It has been confirmed by XRD measurement that the deposited layers mainly consist of ZnTe phases. The PEC measurements indicate that the ZnTe layers are p-type in electrical conduction and optical absorption measurements show that their bandgap is in the range 2.10–2.20 eV. p-Type ZnTe window materials have been used in CdTe based solar cell structures, following new designs of graded bandgap multi-layer solar cells. The structures of FTO/ZnTe/CdTe/metal and FTO/ZnTe/CdTe/CdHgTe/metal have been investigated. The results are presented in this paper using observed experimental data.

Synchrotron X-ray diffraction study of ZnTe at high pressure

ZnTe has been studied at high pressure to 76 GPa and at room temperature in a diamond-anvil cell using angle-dispersive X-ray diffraction technique with synchrotron radiation and an imaging plate detector. The equation-of-state parameters of the two high-pressure phases of ZnTe were for the first time derived to be B 0 = 91.3 ( 7.0 ) GPa and B 0 ′ = 0.8 ( 1.0 ) for the cinnabar-type phase and B 0 = 134 ( 5 ) GPa and B 0 ′ = 2.4 ( 1 ) for the Cmcm-type phase, respectively.

Solid-State Synthesis of ZnTe in Shock Waves

Shock front velocities in a heterogeneous stoichiometric zinc-tellurium mixture in cylindrical capsules were measured at normal and elevated temperatures. In the range of preheating temperatures of 150–300°C, the velocity of a strong shock wave was found to increase by 0.91 km/sec, which is attributed to the occurrence of an exothermic reaction in the zone of high dynamic pressures with an increase in the specific volume. The average velocity of a weak shock wave increased by 0.31 km/sec in the far region of the reaction cell as the preheating temperature of the stoichiometric Zn-Te mixture increased by 150°C. X-ray structure analysis of the shock-recovered products showed almost complete transformation of the reactants with the formation of the cubic ZnTe phase. Theoretical calculations of the acceleration of the shock front velocity due to the reaction in the Zn-Te mixture were conducted. The occurrence of solid-state detonation in the tested mixture is assumed.

Vibrational properties of ZnTe at high pressures

Raman spectra of ZnTe were measured under hydrostatic pressuresup to 15 GPa at T = 300 K. Results for the frequencies offirst- and second-order Raman features of the zincblende phase(0-9.5 GPa) are used to set up a rigid-ion model of the phonondispersion relations under pressure. Calculated phonon densitiesof states, mode Grüneisen parameters and the thermalexpansion coefficient as a function of pressure are discussed.The effect of pressure on the widths and intensities of Ramanspectral features is considered. Raman spectra of high-pressurephases of ZnTe are reported. These spectra indicate the possibleexistence of a new phase near 13 GPa, intermediate between thecinnabar and orthorhombic (Cmcm) phases of ZnTe.

Properties of As–Te alloys and their reactions with Zn substrate

The equilibrium phase relationship, glass formation, glass transition temperature, microhardness and density of As–Te alloys are examined. It is found that the available As–Te equilibrium phase diagram might not be correct, and a possible phase diagram is proposed. As–Te glasses are formed in quenching processes, and the As–Te alloys in the compositional range near As0.5Te0.5 have the highest glass formation ability (GFA). Besides studies of the properties of As–Te alloys, their interfacial reactions with Zn substrate are also investigated. ZnTe phase is formed in the As0.271Te0.729 alloy/Zn reaction couple annealed at 380 and 395°C. Schematic isothermal sections of the As–Te–Zn ternary systems are proposed based on the limited ternary phase equilibria data and the equilibrium phase diagrams of its three constituent binary systems. The reaction paths of the As–Te/Zn couples in both temperatures are liquid/ZnTe/Zn, and are consistent with the proposed isothermal sections.

Effect of Cu-doping on the morphology of ZnTe films electrodeposited from nonaqueous bath

Electrodeposition of Cu-doped ZnTe has been studied in a bath containing ZnCl 2, TeCl 4, KI and CuCl 2 at 160°C using cyclic voltammetry in the dark and under illumination. X-ray diffraction as well as scanning electron microscopy techniques have been employed to investigate the influence of deposition potential on the structure and surface morphology of the electrodeposit. It is shown that a mixed cubic as well as hexagonal ZnTe film is electrodeposited even at a potential lower than the equilibrium potential of Zn electrodeposition. Intermediate electrodeposition potential (−0.7 V to −0.75 V) favours growth of a mixed Te and ZnTe phase. Compact, globular and single phase ZnTe can be grown at −0.95 V. The atomic force microscopic examination of the ZnTe films deposited at −0.95 V indicated compact and close packed granular growth.