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Quantum dots (QDs) have attracted significant interest because of their tunable bandgaps, which enable numerous applications in fields such as photovoltaics, biomedicine, and materials science. This study explores various core electron treatments in the density functional theory (DFT) analysis of II-VI semiconductor quantum dots and their bulk counterparts. We compared All-electron (AE), Effective Core Potential (ECP), All-Electron Relativistic (AER), and DFT-Semicore pseudopotential (DSPP) treatments. Our findings indicate that the AE treatment aligns closely with the experimental results for smaller QDs, whereas the accuracy of DSPP increases with larger QDs. DSPP provides an optimal balance between computational efficiency and accuracy, making it suitable for studying II-VI QDs. Notably, the bandgap behavior varies, being direct for zinc and cadmium chalcogenides, whereas mercury chalcogenides are zero-gap semiconductors (semimetals). The inner bonds of the QDs exhibit an ionic character, whereas the terminal bonds display a covalent character. This study enhances our understanding of the structural and electronic properties of II-VI quantum QDs, aiding their application in various technologies. [ABSTRACT FROM AUTHOR]

This paper presents a first-principles investigation of the energy bandgaps of Cd1−xZnxTe, Cd1−xZnxSe and Cd1−xZnxS semiconductor alloys in zinc-blende crystals. The theoretical analysis is based on the full-potential linearized augmented plane wave method within both generalized gradient and local density approximations. Tran–Blaha-modified Becke–Johnson exchange potential was invoked to accurately provide bandgaps and their bowing parameters. A moderate nonlinear dependence with average bowing parameters around b ~ 0.49 eV for Cd1−xZnxTe, b ~ 0.68 eV Cd1−xZnxS, and b ~ 0.63 eV for Cd1−xZnxSe was found. The origin of the nonlinearity is discussed in light of Zunger's approach to conclude that it arises mainly from volume deformation. [ABSTRACT FROM AUTHOR]

The II–VI semiconductor thin films have vast applications in optoelectronics. Cadmium telluride (CdTe) is one such material, which has proved to be useful in the fabrication of solar cells, photodetectors, etc. In the present work, CdTe thin films have been deposited on glass substrates by thermally evaporating CdTe powder under a high vacuum. The optimum film thickness for photovoltaic applications was determined by performing a detailed characterization of the films. The thermal evaporated CdTe films were found to be polycrystalline with a cubic structure. Considerable improvement in the crystallinity was observed with the increase in thickness. The lattice constant, dislocation density, strain, and stress have also been analyzed. The optical properties of the CdTe films have been observed to change with thickness. The maximum optical absorption was found in the near infrared region. The photoluminescence spectra showed a prominent peak, corresponding to the band-edge transition of the CdTe films. The electrical properties of the films were found to improve with thickness. The films yield maximum photocurrent at 820 nm. Based on the detailed characterization, the film thickness of 950 nm was found to be most suitable for photovoltaic application. [ABSTRACT FROM AUTHOR]

Peculiar and unique growth mechanisms involved in semiconductor nanowires (NWs) pave the way to the achievement of new crystallographic phases and remarkable material properties, and hence, studying polytypism in semiconductor NWs arouses a strong interest for the next generation of electronic and photonic applications. In this context, the growth of ZnS nanowires has been investigated, as bulk ZnS compound exhibits numerous unstable polytypes at high temperatures, but their stable occurrence is highly anticipated in a nanowire due to its special quasi-dimensional shape and growth modes. In this work, the idea is to provide a change in the growth mechanism via the physical state of catalyst droplet (liquid or solid) and hence, study the induced structural modifications in ZnS nanowires. The HRTEM images of VLS (via liquid alloyed catalyst) grown ZnS NWs show periodic stacking faults, which is precisely identified as a stacking sequence of cubic or hexagonal individual planes leading to an astonishing 15R crystal polymorph. This crystallographic phase is observed for the first time in nanowires. Contrastingly, NWs grown with VSS (via solid catalyst) show crystal polytypes of zinc blende and wurtzite. We calculate and discuss the role of cohesive energies in the formation of such ZnS polytypes. Further, we present the selection rules for the crystallization of such 15R structure in NWs and discuss the involved VLS and VSS growth mechanisms leading to the formation of different crystal phases. [ABSTRACT FROM AUTHOR]

Electronic band structures of B- and C-doped ZnO monolayers (ML) at high doping concentration are studied based on spin-polarized plane-wave DFT with Projector Augmented Wave Potentials and Generalized Gradient Approximation. Our results show that both the B- and C-doped structures at 3.13% impurity atom per supercell exhibit half-metallic ferromagnetic behaviour due to the spin-polarized 2p orbitals of the dopant atom, which are localized within the energy gap of the host lattice. A net magnetic moment of 1μB and 2μB are, respectively, found in the B- and C-doped structures mainly due to the partially filled dopant atom 2 p orbitals. Due to ferromagnetic coupling, magnetic moments from the neighbouring Zn atoms and the subsequent O atoms also contribute to the net magnetic moment. At a higher doping concentration of 6.25% impurity atom per supercell, both the materials completely transformed into metal. It is also found that while C doping maintains its ferromagnetic property at this doping concentration, the B-doped ZnO ML becomes antiferromagnetic metal. Our findings would provide valuable theoretical data for material scientists in fabrication of the doped ZnO ML in laboratory [ABSTRACT FROM AUTHOR]

Clustering of highly lattice-mismatched semiconductor alloys has attracted considerable interest recently. However, strong internal strains and cluster variety are the main disadvantages of such alloys. Zinc blende ZnBVI-rich CdxZn1−xOyB1−yVI (BVI = S, Se, Te) with 4O10Cd identical clusters are proposed to resolve these problems. The decrease in the internal strains is a cause of the cluster formation in ZnS- and ZnSe-rich alloys. The favorable CdO and ZnTe bonding is an additional reason for the cluster occurrence in ZnTe-rich alloys. The cohesive energies of CdSe and ZnSe, stiffness coefficients, bond stretching and bond bending elastic constants of CdSe are calculated. The majority of Cd and oxygen atoms should be in 4O10Cd clusters up to 800°C if the ZnS- and ZnSe-rich alloy contents are, respectively, y ≥ 2.5 × 10−4 and y > 3 × 10−4, and x ≈ 2.5y. The obtained results demonstrate that CdxZn1−xOyB1−yVI materials are promising semiconductors with significantly reduced internal strains and identical polyatomic clusters containing oxygen tetrahedrons. [ABSTRACT FROM AUTHOR]

(111)-oriented CdZnTe semiconductor material exhibits a crystal polarity and hence, a face terminated by Cd atoms, conventionally called (111) A face with an opposite face terminated by Te atoms, called (111) B face. These A and B faces have different properties. Their mechanical properties have been studied by mechanical indentation. Sample surfaces were carefully prepared and mechanically and chemically polished, while the crystalline orientation and material defectivity was monitored on both faces using x-ray rocking curve measurements around the (222) orientation in order to evaluate faces with similar quality. The elastic moduli and hardness values of the A and B faces of CdZnTe were similar. Hardness increased from 0.60 GPa to 0.90 GPa with Zn concentration on the B face as a result of solution strengthening. Crack formation and propagation was carefully studied. Both toughness value and crack resistance were affected by polarity. A model involving plastic dislocation flow is proposed to interpret the results. [ABSTRACT FROM AUTHOR]

HgCdTe (MCT) is a widely used semiconductor material used for manufacturing high-quality infrared detectors. At Sofradir, HgCdTe is grown by liquid phase epitaxy on lattice-matched CdZnTe substrates. Low threading dislocation densities (TDD) in the low 1 × 104 dislocations/cm2 are routinely obtained. Despite these low TDD levels, these dislocations are known to affect the electrical properties of photodiodes. Dislocation electrical behavior needs a deeper understanding in order to improve the manufacturing technology and the photodiode performance. In this study, we use Vickers micro-indentations to inject extra dislocations into dedicated areas of n on p mid-wave infrared photodiodes. The photodiodes were then characterized and analyzed theoretically thanks to I(V) and I(t) measurements under F/3 flux conditions (typical focal plane array illumination) at 110 K. Microindentations were performed close to the photodiodes in order to inject controlled high to very high dislocation densities. The effect of such an injection was then studied in depth on photodiodes. The electrical results have shown that the temporal variation of the current I(t) is mostly affected by the generation of extra dislocations. The same type of degradation of I(t) was observed in focal plane arrays, which confirms that dislocations play an important role in the generation of noise defects. [ABSTRACT FROM AUTHOR]

CdS and Ag doped CdS (CdS/Ag) nanoparticles have been prepared via chemical method from a Cadmium acetate precursor and Thiourea. The synthesized CdS and CdS/Ag nanoparticles have been characterized by the X-ray Diffraction and High Resolution Transmission Electron Microscope. Here, these nanoparticles have been synthesized at room temperature and all the characterization have also been done at room temperature only. The XRD results reveal that the products are crystalline with cubic zinc blende structure. HRTEM images show that the prepared nanoparticles are nearly spherical in shape. Williamson-Hall method and Size-Strain Plot (SSP) have been used to study the individual contribution of crystalline sizes and lattice strain on the peak broadening of the CdS and CdS/Ag nanoparticles. The different modified model of Williamson-Hall method such as, uniform deformation model, uniform stress deformation model and uniform energy density deformation model and SSP method have been used to calculate the different physical parameter such as lattice strain, stress and energy density for all diffraction peaks of the XRD, corresponding to the CdS and silver doped CdS (CdS/Ag). The obtained results reveal that the average particle size of the prepared CdS and CdS/Ag nanoparticles estimated from the HRTEM images, Williamson-Hall analysis and SSP method are highly correlated with each other. Further, all these result confirms that doping of Ag significantly affects the elastic properties of CdS. [ABSTRACT FROM AUTHOR]

Significant improvement has been carried out in the field of the II-VI group semiconductor device technology. Semiconductors based on the II-VI group are attractive due to their alternative uses for thermal imaging systems and photonic applications. This study focuses on experimental work on the optical, electrical and structural characterization of an infrared (IR) photodetector zinc selenide (ZnSe). In addition, the IR sensitivity of the ZnSe has primarily been investigated by exploiting the IR responses of the material for various gas pressures, p, and interelectrode distances, d, in the IR converter. The experimental findings include the results of plasma current and plasma discharge emission under various illumination conditions in the IR region. The electron density distributions inside the gas discharge gap have also been simulated in two-dimensional media. Experimentally, the current-voltage, current-time, and discharge light emission plots are produced for a wide experimental parameter range. Consequently, the structural and optical properties have been studied through atomic force microscopy and Fourier-transform infrared spectroscopy techniques to obtain a comprehensive knowledge of the material. [ABSTRACT FROM AUTHOR]

We have studied the first-principle calculations of the effect of hydrostatic pressure on the structural, electronic, and magnetic properties of Cd Z X (Z = Cr, Mn; X = S, Se) DMS in zb (B3) phase. High-pressure behavior of these compounds have been investigated between 0 and 100 GPa The calculations have been performed using density functional theory (DFT) as implemented in code SIESTA using LDA as exchange-correlation (XC) potential. Study of band structures shows half-metallic ferromagnetic nature with 100 % spin polarization. Under application of external pressure, the valence band and conduction band are shifted from their positions, which lead to modification of electronic structure. [ABSTRACT FROM AUTHOR]

We report on Förster resonance energy transfer in the dense arrays of epitaxial quantum dots (QDs), formed by fractional monolayer CdSe insertions within a ZnSe matrix. In such arrays comprising the QDs of different sizes, the energy transfer can take place between the ground levels of small QDs and the excited levels of large radiating QDs, when these states are in resonance. This mechanism provides directional excitation of a limited number of the large QDs possessing the excited levels. It reveals itself by the shrinkage of photoluminescence (PL) bands and the appearance of the narrow single excitonic lines in micro-PL spectra. The strong shortening of characteristic PL decay times in the energy-donating QDs is observed when the distance between them and the energy-accepting QDs decreases. Photoluminescence excitation spectroscopy demonstrates the switching of the dominant energy transfer mechanism at the energy predicted by theoretical modeling of the excitonic levels in the QD arrays. Our results pave the way for engineering of the architecture of excitonic levels in the QD arrays to realize efficient nano-emitters. [ABSTRACT FROM AUTHOR]

Influence on elastic moduli of donor electron d-states of cobalt impurities has been investigated in mercury selenide crystals. Experiments have been carried out at the frequency of 53 MHz in the temperature interval of 1.3-100 K. Softening of the $$(C_{11} - C_{12})/2$$ modulus below 10 K has been observed in the impurity crystals in contrast with the $$(C_{11} + C_{12} + 2C_{44})/2$$ and $$C_{44}$$ moduli those have exhibited hardening at cooling typical for dielectric and semiconductor crystals. The softening of the elastic modulus has been interpreted as manifestation of hybridization of the impurity d-states in the conduction band of the crystal. Comparison of theoretical calculations with experimental data has been proved to be in good agreement and has made it possible to determine the parameters characterizing the hybridized electron states. [ABSTRACT FROM AUTHOR]

$$\hbox {ZnS}_{x}\hbox {Se}_{1-x}$$ single crystals with different S contents were examined. The crystals were grown by the modified Bridgman method. Thermal, optical, and electrical measurements for a solid solution of $$\hbox {ZnS}_{ x}\hbox {Se}_{1-x}$$ crystals are presented and analyzed to determine the influence of composition on the thermal diffusivity, the electrical resistivity, the relative permittivity, and the energy gap. The thermal measurement was based on the thermal wave method with detection using the mirage effect. For interpretation of the experimental data, a thermal model of a layered system was adopted. The results showed that the thermal diffusivity of samples decreases with an increase of the S content $$x$$ . The electrical resistivity of investigated samples was measured by the constant voltage method. The relative permittivity was determined by dielectric spectroscopy and decreased with increasing sulfur content in the ZnSe. Further, the optical bandgap of $$\hbox {ZnS}_{ x}\hbox {Se}_{1-x}$$ was determined from photoluminescence spectra. Possible correlations between the thermal diffusivity, the optical bandgap, and electrical properties were studied. The obtained results showed a clear dependence of those parameters on the S concentration in the sample. [ABSTRACT FROM AUTHOR]

Luminescence spectra of W centers in ZnSe are studied. Radiative d-d transitions are identified by the Tanabe-Sugano diagram of the crystal field theory. It is found that the type of electronic transitions changes with a significant change in spectral characteristics of impurity radiation during the transition fromthe 3 d- to 5 d-electronic systemof impurity centers in the crystals under study. [ABSTRACT FROM AUTHOR]

Large-scale CdSe nanotube arrays on indium tin oxide (ITO) glass have been synthesized using ZnO nanorod template. The strong visible light absorption in CdSe, its excellent photoresponse, and the large surface area associated with the tubular morphology lead to good visible light-driven photocatalytic capability of these nanotube arrays. Compared to freestanding nanoparticles, such one-piece nanotube arrays on ITO make it very convenient for catalyst recycling after their usage. [ABSTRACT FROM AUTHOR]

Large-area, low-cost substrates are envisioned for next-generation HgCdTe infrared focal-plane arrays (IRFPA). Si, GaAs, Ge, and InSb have been previously examined as potential candidates. Fabrication of IRFPAs based on these substrates is limited by fundamental materials properties that potentially lead to lower detector performance and operability. Lattice and thermal mismatch between the substrate and epilayer are just two of several material factors that must be considered. We have reviewed these factors in the context of more recent data, and determined it worthwhile to revisit the use of GaAs substrates for epitaxial growth of HgCdTe. Our study starts with an evaluation of the surface quality (epireadiness) of commercially available (211) B-oriented GaAs substrates. Molecular beam epitaxial growth of CdTe buffer layers and subsequent HgCdTe absorber layers are performed in separate vacuum-interconnected chambers. The importance of optimization of the CdTe buffer layer growth for high-quality HgCdTe is detailed through surface morphology and x-ray studies. x-Ray diffraction rocking-curve full-width at half-maximum values as low as 52 arcsec have been obtained. Long-wave infrared HgCdTe ( x = 0.23) has been grown on these buffer layers, producing cross-hatch-dominated surface morphologies, with dislocation densities as low as ∼3 × 10 cm. We have also obtained (for optimized layers), 80-K Hall-effect n-type carrier concentration and electron mobility of approximately ~1.5 × 10 cm and 1 × 10 cm V s, respectively. Finally, we briefly compare GaAs and Si in light of our preliminary investigation. [ABSTRACT FROM AUTHOR]

This paper presents experimental and theoretical piezoelectric photoacoustic spectra of ZnSe samples after different surface treatments: grinding, polishing, and etching. The modification of the Jackson and Amer theory, presented in the paper, enabled numerical interpretation of the spectra in the model of a mechanically damaged surface layer. The nature of the characteristic peak observed at E = 2.65 eV below the energy gap is explained as caused by the Urbach absorption tail and the damaged surface layer of a sample. The correlation between the microhardness of the ZnBeSe and ZnSe crystals and the thickness of the mechanically damaged surface layer was observed. [ABSTRACT FROM AUTHOR]

Wurzite ZnS:Mn nanorods are synthesized via a solvothermal method by using ethylenediamine and water as mixed solvent. The diameters of the nanorods increase and the lengths decrease with the Mn concentration. High resolution transmission electron microscopic images illustrate that a few cubic ZnS:Mn nanoparticles arise along with hexagonal nanorods on high Mn concentration. The samples set off yellow-orange emission at 590 nm, characteristic of T→A transition of Mn at T symmetry in ZnS. Electron spin resonance spectrum of the nanorods shows that high Mn concentrations produce a broad envelope, whereas six-line hyperfine appears for lower Mn concentrations. These results together with the magnetization curves indicate that all the ZnS:Mn samples are paramagnetic even down to 4 K, which suggests that the ZnS:Mn is not suitable for dilute magnetic semiconductor. [ABSTRACT FROM AUTHOR]

In this study, unique three-dimensional ZnMnO hierarchical hollow microspheres (HHMs) with diameters of 5-8 μm have been synthesized by a simple hydrothermal approach. In particular, room-temperature magnetization measurements indicate that novel co-existence of ferromagnetism (FM)/paramagnetism (PM) and only PM behaviors for the as-annealed ZnMnO HHMs at 673 and 1,073 K, respectively, in Ar gas atmosphere appear, whereas the as-synthesized ones show merely pure FM. Based on the Photoluminescence and Raman spectra, it is confirmed that the concentrations of oxygen vacancies in ZnMnO HHMs were becoming larger and larger with increasing annealing temperature. Corresponding magnetic evolution mechanism is proposed to relate to oxygen vacancies based on annealing processes. This novel magnetic property will enrich our understanding of diluted magnetic semiconductors. [ABSTRACT FROM AUTHOR]

Large-scale amorphous wire-like ZnO nanostructures were prepared by ultrasonic spray pyrolysis Zn(CO) without involvement of any template or patterned catalyst. The as-obtained amorphous ZnO nanowires were characterized using scanning/transmission electron microscopy, X-ray diffraction/photoelectron spectroscopy, energy-dispersed X-ray spectrometry, selected area electronic diffraction, and high-resolution transmission electron microscopy. The results reveal the as-made noncrystalline samples are about 30-60 nm in diameter and several tens of microns in length and the growth mechanism is tentatively proposed as the self-assembly soft template mechanism. The photoluminescence spectra in all of the as-studied specimens exhibit one wide visible emission peak in about 508 nm. The corresponding PL intensity greatly increased with an annealing temperature, which has an application for a high efficiency vacuum fluorescent displays and a low-voltage phosphor. [ABSTRACT FROM AUTHOR]

We realized laser generation on a Fe:ZnTe crystal for first time. The crystal was pumped at room temperature by 40 ns pulses of an Er:YAG laser operating at a wavelength of 2.94 μm in the Q-switching mode. The output energy of the Fe:ZnTe laser was 0.18 mJ at a slope efficiency of 2.4% with respect to absorbed pumping energy. We achieved tuning of the Fe:ZnTe laser generation wavelength within the range of 4.35-5.45 μm using a prism-dispersion cavity. [ABSTRACT FROM AUTHOR]

ZnO and ZnSe are proposed as n-type layers in ZnTe heterojunction diodes to overcome problems associated with the n-type doping of ZnTe. The structural properties and electrical characteristics of ZnO/ZnTe and ZnO/ZnSe/ZnTe heterojunctions grown by molecular beam epitaxy on (001) GaAs substrates are presented. ZnO shows a strong preference for c-plane (0001) orientation resulting in a nonepitaxial relationship and high density of rotational domains for growth on ZnTe (001). ZnSe/ZnTe structures demonstrate a (001) epitaxial relationship with high density of {111} stacking faults originating at the heterojunction interface. ZnO/ZnSe/ZnTe heterojunction diodes show excellent diode rectification and clear photovoltaic response with open-circuit voltage of V = 0.8 V. [ABSTRACT FROM AUTHOR]

series of bar-shaped samples consisting of lateral arrangements of alternating ZnO:Al and ZnO stripes was fabricated by radiofrequency (RF)-sputtering and microfabrication techniques on glass substrates. Throughout the series, the number of interfaces between ZnO and ZnO:Al was varied whilst the material fractions of ZnO:Al and ZnO within the bars were not altered. Lateral thermoelectric transport parameters, i.e., Seebeck effect and electrical resistivity, were measured as a function of temperature for all microstructured samples and two reference samples of ZnO:Al and undoped ZnO. The transport direction through the bar was perpendicular to the stripe direction, such that the electrons and phonons have to pass all interfaces. The transport coefficients of the microstructured samples show clear dependence on the number of interfaces between ZnO and ZnO:Al. Thermoelectric measurements, photoluminescence, and Raman measurements indicate that this is due to diffusion of Al donors along the grain boundaries into the undoped ZnO stripes, which takes place during the fabrication process. Modeling of the dependence of the Seebeck coefficient and the resistivity of the series of samples on the basis of a network model accounting for donor diffusion supports these findings. [ABSTRACT FROM AUTHOR]

We investigate light emission from ZnTe-based microcavities containing CdTe quantum dots (QDs), with 2D (planar cavity) and 0D (pillar cavities) photonic confinement. The angular distribution from the planar cavity is presented as well as 2D cross-sections of the far field distribution of radiation from the micropillars. The efficient and desirable modification of the isotropic radiation of the QDs is shown for such structures. The diffraction observed is found to be inherent for such experiments with large numerical aperture of the lens and small diameters of the investigated pillars. This diffraction is successfully modeled. [ABSTRACT FROM AUTHOR]

The search for above room temperature ferromagnetism in dilute magnetic semiconductors has been intense in recent year. Arrays of perpendicular ferromagnetic nanowire/rods have recently attracted considerable interest for their potential use in many areas of advanced nanotechnology. We report a simple low-temperature chemical vapor deposition (CVD) to create self-assembled comb-like Ni-/undoped ZnO nanostructure arrays. The phases, compositions, and physical properties of the studied samples were analyzed by different techniques, including high-resolution X-ray diffraction/photoelectron spectroscopy/transmission electron microscopy, photoluminescence, and MPMS. In particular, the Ni-doped ZnO nanocombs (NCs) with ferromagnetic and superparamagnetic properties have been observed whereas undoped ZnO NCs disappear. The corresponding ferromagnetic source mechanism is discussed, in which defects such as O vacancies would play an important role. [ABSTRACT FROM AUTHOR]

This paper describes molecular-beam epitaxy growth of mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) dual-band device structures on large-area (6 cm × 6 cm) CdZnTe substrates. Wafer-level composition and defect mapping techniques were used to investigate the limiting mechanisms in improving the cutoff wavelength ( λc) uniformity and reducing the defect density. Structural quality of epitaxial layers was monitored using etch pit density (EPD) measurements at various depths in the epitaxial layers. Finally, 640 × 480, 20- μm-pixel-pitch dual-band focal-plane arrays (FPAs) were fabricated to demonstrate the overall maturity of growth and fabrication processes of epitaxial layers. The MWIR/LWIR dual-band layers, at optimized growth conditions, show a λc variation of ±0.15 μm across a 6 cm × 6 cm CdZnTe substrate, a uniform low macrodefect density with an average of 1000 cm−2, and an average EPD of 1.5 × 105 cm−2. FPAs fabricated using these layers show band 1 (MWIR) noise equivalent temperature difference (NETD) operability of 99.94% and band 2 (LWIR) NETD operability of 99.2%, which are among the highest reported to date. [ABSTRACT FROM AUTHOR]

Inductively coupled plasmas (ICP) are the high-density plasmas of choice for processing HgCdTe and related compounds. Real-time examination of the ICP plasmas used to process HgCdTe would be desirable. In this preliminary study, the feasibility of using optical emission spectroscopy (OES) of ICP plasma used for processing HgCdTe has been examined. We have examined the utility of OES as a real-time diagnostic tool for HgCdTe device fabrication. In this preliminary study it has been found that mercury and cadmium can be detected but are dependent on several factors: sample area, material composition, etch rate, sample temperature, photoresist area, and plasma power. Furthermore, we found strong correlation between the amount of hydrogen detected by OES for samples with photoresist versus samples without photoresist while processing with hydrogen-based plasma. Hydrogen emission intensity decreased dramatically in samples with photoresist, contrary to the theory that photoresist adds hydrogen to the plasma effluent. It appears that hydrogen complexes with photoresist, reducing the global amount of hydrogen during the process. Furthermore, this phenomena may help to explain macroloading issues whereby additional photoresist area slowed HgCdTe, CdTe, and photoresist etch rates. [ABSTRACT FROM AUTHOR]

Thin epitaxial CdTe films were grown on CdTe(111)B substrates by the close-spaced sublimation (CSS) technique and were characterized over a range of experimental parameters. The source temperature was varied between 480°C and 540°C, maintaining an average constant source–substrate temperature difference Δ T of ∼130°C. Helium was used as a carrier gas at pressures between 2 Torr and 10 Torr. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) were used to analyze the film morphology and structure. Growth rates ranging from 1 μm/h to 4 μm/h were observed, based on profilometer thickness measurements. The addition of a pre-growth heat treatment step and post-growth annealing treatment resulted in smooth CdTe(111) films. An evolution in growth morphology was demonstrated with SEM images and film quality was confirmed with XRD. [ABSTRACT FROM AUTHOR]

The scope of the present investigation is to make a clear contrast between the bandgap bowing characters of III–V and II–VI compound-semiconductor common-cation ternary alloys. For this aim, both the sp3 s* tight-binding method, with the inclusion of spin–orbit coupling, and the full-potential linear augmented plane-wave technique are used to calculate the partial and total densities of states, the constituent ionicity, and the total electron charge density for the common-cation GaSb xAs1− x and CdSe xTe1− x ternary alloys. The results show that the bowing is sensitive to competition between the anions for trapping/losing electric charges. The lack of this competition would result in complete absence of the bowing, as is the case for common-anion ternary alloys. In the common-cation ternary alloys studied herein, the bowing is found to be proportional to the electronegativity of the anions χanion (i.e., the 6-valency anions are more electronegative than the 5-valency ones, and consequently the former result in stronger intercompetition and yield stronger bowing in the II–VI alloys) and also proportional to the relative mismatch in electronegativity between the competing anions $$({\Updelta}\chi^{\rm{anion}}/\chi^{\rm{anion}}_{\rm{ave}}).$$ The excellent agreement between our theoretical results and recent photoluminescence data corroborates our claim. [ABSTRACT FROM AUTHOR]

The tapered CdS nanobelts and CdSe nanowires were prepared by hydrogen-assisted thermal evaporation method. Different supersaturation leads to two different kinds of 1D nanostructures. The PL measurements recorded from the as-prepared tapered CdS nanobelts and CdSe nanowires show only a bandgap emission with relatively narrow full-width half maximum, which means that they possess good optical property. The as-synthesized high-quality tapered CdS nanobelts and CdSe nanowires may be excellent building blocks for photonic devices. [ABSTRACT FROM AUTHOR]

Langmuir Blodgett (LB) process is an important route to the development of organized molecular layered structures of a variety of organic molecules with suitably designed architecture and functionality. LB multilayers have also been used as templates and precursors to develop nano-structured thin films. In this article, studies on the molecular packing and three-dimensional structure of prototypic cadmium arachidate (CdA), zinc arachidate (ZnA) and mixed CdA-ZnA LB multilayers are presented. The formation of semiconducting nano-clusters of CdS, ZnS and CdxZn1-xS alloys within the organic multilayer matrix, using arachidate LB multilayers as precursors is also discussed. [ABSTRACT FROM AUTHOR]

We are engaged in a systematic study of the optical and laser properties of Cr2+-doped cadmium chalcogenides. Previously, we demonstrated quasi-continuous wave lasing from Cr2+-doped Cd0.55Mn0.45Te with slope efficiencies as high as 64% and a laser tuning range from 2,170–3,010 nm. In this paper, we report the first demonstration of lasing from Cr:CdTe at room temperature. Pulsed-laser operation was obtained with a free-running spectrum centered at 2,535 nm. The slope efficiency of the laser was low (∼1%) because of large parasitic losses at the laser wavelength. The spectroscopic properties of Cr:CdTe are favorable for laser applications because of a large emission cross section (∼2.5 × 10−18 cm2) and a high emission-quantum yield (∼88%). In addition, CdTe can easily incorporate Cr ions either through melt growth or diffusion doping. Along with our results on Cr2+:CdTe, we report on the optical properties of several other Cr2+-doped II-VI semiconductors (ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, Cd0.9Zn0.1Te, Cd0.65Mg0.35Te, Cd0.85Mn0.15Te, and Cd0.55Mn0.45Te) and compare them for applications as solid-state laser materials. [ABSTRACT FROM AUTHOR]

Recently, efficient spin injection, being the first step towards semiconductor spin electronics, by using BeMnZnSe as a spin filter was accomplished. Such a spin filter made it possible to align the spin orientation of conduction electrons and subsequently inject them into GaAs. However, controlling spin orientation of conduction electrons by an external voltage would be very desirable for semiconductor-based magnetoelectronics. This can be accomplished by using spin switch structures, based on resonant tunneling through magnetic quantum wells, with two separate spin-up and spin-down resonances. Here we summarize both our recent results on spin injection as well as on spin aligner and magnetic resonant tunneling structures. For accomplishing the latter, we have developed magnetic resonant tunneling diodes based on BeTe–ZnMnSe–BeTe structures. Resonant tunneling diode is meant to serve as a spin switch because of the existence of two separate spin-up and spin-down resonances. The tunneling carriers have subsequently been injected into a nonmagnetic GaAs p–i–n light emitting diode. Circular polarization of the emitted light is an indicator of the spin polarization of injected electrons. At constant magnetic field and current, degree of spin polarization could be changed from 81% to 38% by only varying the voltage across the magnetic resonant tunneling device. [ABSTRACT FROM AUTHOR]

We have determined the dielectric function of BeTe and BexZn1−xSe for the full composition range (0≤x≤1) by spectroscopic ellipsometry in the ultraviolet- and vacuum ultraviolet-range. The spectra show pronounced features in the photon energy range between 2.7 and 25 eV. For BeTe, we assign the main structures to interband transitions from the heavy and light hole bands to the lowest conduction band at high symmetry points in the Brillouin zone. The spectral positions of the interband critical points agree with quasiparticle excitations obtained by a GW calculation. We extracted the dielectric function of BeTe in the transparent regime below the fundamental gap E0 at 4.2 eV from our experimental data using the three-phase model (vacuum/BeTe/GaAs). By comparing the ZnSe spectra (x=0) to literature data, we assign the observed structures to interband transitions at specific points or regions of the Brillouin zone. The corresponding assignment for BeSe is made by tracking the dependence of these structures on Be content x from x=0 to x=1. E0 has the steepest slope dE0/dx and exhibits a bowing vs x. For samples with a large Zn content (x<0.2) two structures show up at high energies (15.7 and 16.9 eV) which have not been observed before. We assign these structures to transitions from the Zn 3d bands to a higher conduction band at the L point and at the γ point. [ABSTRACT FROM AUTHOR]

Advances in experimental techniques are the life blood of technology and science. Some of these are occurring via development of new techniques using synchrotron radiation (SR). Of particular interest are techniques developed in support of the long range plan of the Si integrated circuit (IC) industry (the “roadmap”) to strongly reduce the feature size in IC well into the next century. Two newly developed and/or improved SR techniques are examined. First is the investigation of the electrical deactivation mechanism in Si with very large (e.g., 2×10 20/cm3) As doping. Here newly developed standing wave spectroscopy techniques are used. Second, the use of total reflection x-ray fluorescence to detect metallic atoms on Si production wafers. The general advantages of SR are also outlined. [ABSTRACT FROM AUTHOR]

Atomic hydrogen is shown to be particularly efficacious for the preparation of substrates for subsequent growth of II-VI compounds by molecular beam epitaxy. A commercial thermal cracker was used to produce atomic hydrogen in the molecular beam epitaxy growth chamber for in-situ cleaning. This paper discusses the use of atomic hydrogen for both oxide removal from GaAs prior to ZnSe and CdTe growth, and for low-temperature oxide removal from CdTe and HgCdTe. Reflection high energy electron diffraction, ultra violet fluorescence microscopy, Nomarski interference contrast microscopy, and atomic force microscopy were used to characterize the growths. [ABSTRACT FROM AUTHOR]

The first detailed comparison has been made of the metalorganic vapor phase epitaxy growth rates of CdTe, ZnTe, and ZnSe, measured in situ with laser reflectometry. The comparison also includes the photo-assisted growth with visible radiation from an argon ion laser. Using a standard Group II precursor (DMCd or DMZn.TEN) partial pressure of 1.5 × 10−4 atm, VI/II ratio of 1 and DIPM (M = Te, Se) the maximum growth rates are in the region of 10 to 15 AU/ s. Decrease in growth rates of ZnTe at higher temperatures or higher laser powers have been attributed to the desorption from the substrate of unreacted Te precursor. The behavior of DTBSe is quite different from DIPSe for both pyrolytic and photo-assisted growth. The maximum growth rate is around 1 AU/ s with very little photo-enhancement, except at 300°C. Secondary ion mass spectroscopy analysis of hydrogen concentration in the ZnSe layers shows high concentrations, up to 5.9 × 1019 atoms cm−3 for DTBSe grown ZnSe under pyrolytic conditions. These results show that the growth kinetics play an important part in the incorporation of hydrogen and passivation of acceptor doped material. [ABSTRACT FROM AUTHOR]

We report the observation of the quantum-confined Stark effect (QCSE) in ZnSe/ ZnCdSe single quantum wells grown by molecular beam epitaxy, using photoluminescence. In our experiments the electric field was applied via a reverse-biased Schottky barrier contact. To our knowledge, this is the first observation of the QCSE in any wide gap II-VI semiconductor heterostructure. Significant red shifts, typically 10-15 meV, are detected before quenching. An associated reduction in the transition intensity, consistent with the QCSE. is clearly observed. The dependence of these results will be discussed as a function of quantum well depth and thickness. Complete quenching of the luminescence is observed with applied voltages as low as 5 V. In addition, at lowest voltages, we also detect small blue shifts (up to 4 meV), which we attribute to the interaction between the externally applied electric field and the built-in field of the structure. [ABSTRACT FROM AUTHOR]

A systematic study was conducted on electrical properties of metal-semiconductor contacts to n-ZnSSe with metals of different metal work functions. A clear relation was found between the Schottky barrier height and the metal work function although the Schottky contact theory could not predict it accurately. Thermionic-emission was found to be the dominant current transport mechanism. A significant Schottky barrier height improvement was achieved by means of a cryogenic process technique for forming the Au/n-ZnSSe contact. A thermal stability study was also conducted on Pd and Au/n-ZnSSe contacts. Thermal annealing tests showed a stable electrical property up to T = 250°C for the Pd contact and T = 150°C for the Au contact, however, a dramatic degradation was observed after higher temperature annealing and this is attributed to the interaction between metals and ZnSSe after annealing as supported by Auger electron spectroscopy. [ABSTRACT FROM AUTHOR]

We report on the observation of the doubly resonant secondary emission involving 2 s and 1 s exciton states. The resonance conditions have been realized in CdTe/CdMn Te quantum well structures by magnetic-field tuning of the 2 s-1 s energy spacing to the LO-phonon energy. Theoretical analysis shows the doubly resonant process to be indirect, with hot 1 s excitons acting as intermediate states. It is concluded that the resonance width of 2.6 meV gives the 2 s-exciton homogeneous linewidth governed by elastic scattering into the hot 1 s exciton states. [ABSTRACT FROM AUTHOR]

We discuss the exciton centre-of-mass dispersion in a (Ga,Al)As-GaAs-AlAs-(Ga, Al)As quantum well taking into account the Γ- X coupling. The position of the Γ and X quantum well levels is monitored by applying an external electric field. Near the degeneracy, the coupling plays an important role mixing the Γ and X levels. As a consequence, the exciton in-plane mass presents a significant non-parabolicity as its values change from a Γ-reduced mass to a X-reduced mass. [ABSTRACT FROM AUTHOR]

Precise-temperature-dependent measurements of energy of excitons confined in CdTe/CdMnTe quantum wells and superlattices were performed between 2 K and 100 K. We show that magnetic fluctuations lead to a variation of the valence band offset, in agreement with a model proposed previously for bulk materials. [ABSTRACT FROM AUTHOR]

Time-resolved photoluminescence experiments in a wide carrier density range up to and beyond the threshold for stimulated emission in ZnSe/ZnSSe superlattices are presented. Different localisation mechanisms of free excitons are identified giving rise to different radiative recombination channels. At high carrier density localised energy states merge into miniband that allows for exciton-exciton interaction, such as screening of the free-exciton absorption and inelastic exciton-exciton scattering. [ABSTRACT FROM AUTHOR]

Interaction of two magnetic polarons formed either by single carriers or by excitons is considered in bulk crystal, quantum well and quantum wire. It is shown that the magnetic bipolaron can be formed if the distance between two polarons is less than some critical value. This critical radius is the larger the lower the dimensionality of the system, the lower the temperature and the larger the single-polaron radius. The critical distance for the neutral-magnetic-bipolaron formation is much longer than for the charged bipolaron. [ABSTRACT FROM AUTHOR]

The spectra of transmission and reflection of synthetic opal which has 3-dimensional periodic structure were measured at different orientations of incident beam relative to the sample facets. It is shown that opal behaves as «semi-metallic» photonic band gap (PBG) material in the vicinity of photon energy 2.3 eV. The synthesis of CdS microcrystals embedded in the pores of opal was made for the first time in an attempt to form a system of quantum dots. Optical spectra (reflection and transmission, photoluminescence and Raman scattering) were studied. The results demonstrate good crystallinity of microcrystals embedded in opal matrix and exhibit well-pronounced quantum confinement effects in fundamental edge absorption spectra. The spectral overlap of the PBG of opal with electronic band gap of many of II-VI semiconductors seems to make opal/semiconductor system a promising media for experimental studies of such PBG-related effects as inhibition of spontaneous emission, microcavity polariton, etc. [ABSTRACT FROM AUTHOR]

The magnetic contribution to the specific heat of bulk crystals of Zn1− xMn xTe ( x = 0.03) heavily (up to 1019 cm−3) p-type doped with P is studied over the temperature range 0.5–15 K and magnetic field range 0–3 T. The magnetic specific heat observed at zero magnetic field indicates that a substantial part of the magnetic ions has the degeneracy of their magnetic ground state lifted by d– d and p– d exchange interactions. The effect increases for doped and annealed samples with higher concentration of conducting holes. We have also carried out a theoretical analysis that takes into account the contributions due to small magnetic clusters, single magnetic ions in crystal field of distorted crystal lattice, and low energy excitations of the p– d exchange-coupled system of local moments and carriers. [ABSTRACT FROM AUTHOR]