Nanostructured ZnTe films prepared by D.C. magnetron sputtering
TL;DR: The shift of the band gap to higher energies depended on the relative magnitudes of substrate temperature and gas pressure during deposition as mentioned in this paper, and the relative magnitude of temperature and pressure during the sputtering of a ZnTe target was determined.
Abstract: ZnTe films in nanostructured form have been deposited by high pressure d.c. magnetron sputtering of a ZnTe target onto different substrates kept at various temperatures ranging from 223–373 K. Shift of the band gap to higher energies depended on the relative magnitudes of substrate temperature and gas pressure during deposition.
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Journal Article•
TL;DR: In the limit of a QD much smaller than the bulk exciton size, the linear spectrum will be a series of lines, and the phonon broadening of these lines is considered.
Abstract: We analyze theoretically the optical properties of ideal semiconductor crystallites so small that they show quantum confinement in all three dimensions [quantum dots (QD's)]. In the limit of a QD much smaller than the bulk exciton size, the linear spectrum will be a series of lines, and we consider the phonon broadening of these lines. The lowest interband transition will saturate like a two-level system, without exchange and Coulomb screening. Depending on the broadening, the absorption and the changes in absorption and refractive index resulting from saturation can become very large, and the local-field effects can become so strong as to give optical bistability without external feedback. The small QD limit is more readily achieved with narrow-band-gap semiconductors.
788 citations
TL;DR: The optical absorption in these films could be explained by the combined effects of phonon and inhomogeneity broadening along with optical loss due to light scattering at the nanocrystallites.
Abstract: Nanocrystalline ZnS films with different thickness (10–40 nm) were deposited onto quartz and NaCl substrates by magnetron sputtering of a ZnS target in argon plasma. All the films showed a zinc blende structure and the photoluminescence peak positions depended on the surface to volume ratio of the films. The optical absorption in these films could be explained by the combined effects of phonon and inhomogeneity broadening along with optical loss due to light scattering at the nanocrystallites.
61 citations
TL;DR: In this paper, structural, morphological, optical and electrical properties of ZnTe films were investigated as a function of substrate temperature (at −123 and 27°C) and post-deposition annealing temperature ( at 200, 300 and 400°C).
Abstract: The structural, morphological, optical and electrical properties of ZnTe films deposited by evaporation were investigated as a function of substrate temperature (at −123 and 27 °C) and post-deposition annealing temperature (at 200, 300 and 400 °C). It was determined that films deposited at both substrate temperatures were polycrystalline in nature with zinc-blende structure and a strong (1 1 1) texture. A small Te peak was detected in XRD spectra for both substrate temperatures, indicating that as-deposited ZnTe films were slightly rich in Te. Larger grains and a tighter grain size distribution were obtained with increased substrate temperature. Scanning electron microscopy (SEM) studies showed that the microstructures of the as-deposited films agreed well with the expectations from structure zone model. Post-deposition annealing induced further grain growth and tightened the grain size distribution. Annealing at 400 °C resulted in randomization in the texture of films deposited at both substrate temperatures. Optical spectroscopy results of the films indicated that the optical band gap value increased from 2.13 to 2.16 eV with increased substrate temperature. Increasing the annealing temperature sharpened the band-edge. Resistivity measurements showed that the resistivity of films deposited at substrate temperatures of −123 and 27 °C were 32 Ω cm, and 1.0 × 104 Ω cm, respectively with corresponding carrier concentrations of 8.9 × 1015 cm−3 and 1.5 × 1014 cm−3. Annealing caused opposite changes in the film resistivity between the samples prepared at substrate temperatures of −123 and 27 °C.
58 citations
TL;DR: In this article, a Schottky junction in the configuration ITO/nano-CdS/Au has been fabricated and the current(I) −voltage(V) and capacitance(C)−voltage (V) characteristics studied.
Abstract: A Schottky junction in the configuration ITO/nano-CdS/Au has been fabricated and the current(I)–voltage(V) and capacitance(C)–voltage(V) characteristics studied. The I–V studies show series resistance effect resulting in two ideality factors: one in low and the other in high forward bias regime, suggesting the presence of surface/interface traps in nano-CdS. Frequency dependent capacitance has also been studied and different semiconductor parameters have been estimated from the I–V and C–V analysis.
30 citations
TL;DR: In this article, thin films of GaAs were electrochemically prepared from acidic solutions of pure metallic Ga and As 2 O 3, and structural characterization of the nanoparticles were carried out by XRD technique which exhibits partial amorphization of the crystallites in the low electrolysis current regime.
Abstract: Nanoparticulate thin films of GaAs we electrochemically prepared from acidic solutions of pure metallic Ga and As 2 O 3 . Samples of different crystallite sizes were prepared by varying the electrolysis parameters. Structural characterization of the nanoparticles were carried out by XRD technique which exhibits partial amorphization of the crystallites in the low electrolysis current regime. Quantum confinement effect was prominently observed in the optical absorption spectra with blue-shift of absorption onsets with respect to the bulk band gap. Room temperature photoluminescence exhibit band edge luminescence as well as other surface related bands. Incorporation of transition element as impurity leads to enhanced luminescence intensity and generates deep traps.
30 citations
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TL;DR: In this article, the optical properties of ideal semiconductor crystallites so small that they show quantum confinement in all three dimensions [quantum dots (QD's)] were analyzed theoretically, and the phonon broadening of these lines was considered.
Abstract: We analyze theoretically the optical properties of ideal semiconductor crystallites so small that they show quantum confinement in all three dimensions [quantum dots (QD's)]. In the limit of a QD much smaller than the bulk exciton size, the linear spectrum will be a series of lines, and we consider the phonon broadening of these lines. The lowest interband transition will saturate like a two-level system, without exchange and Coulomb screening. Depending on the broadening, the absorption and the changes in absorption and refractive index resulting from saturation can become very large, and the local-field effects can become so strong as to give optical bistability without external feedback. The small QD limit is more readily achieved with narrow-band-gap semiconductors.
843 citations
Journal Article•
TL;DR: In the limit of a QD much smaller than the bulk exciton size, the linear spectrum will be a series of lines, and the phonon broadening of these lines is considered.
Abstract: We analyze theoretically the optical properties of ideal semiconductor crystallites so small that they show quantum confinement in all three dimensions [quantum dots (QD's)]. In the limit of a QD much smaller than the bulk exciton size, the linear spectrum will be a series of lines, and we consider the phonon broadening of these lines. The lowest interband transition will saturate like a two-level system, without exchange and Coulomb screening. Depending on the broadening, the absorption and the changes in absorption and refractive index resulting from saturation can become very large, and the local-field effects can become so strong as to give optical bistability without external feedback. The small QD limit is more readily achieved with narrow-band-gap semiconductors.
788 citations
TL;DR: In this article, the development of bulk optical properties as a function of crystallite size for the inorganic direct gap semiconductor CdS was studied in situ at extreme dilution.
Abstract: This paper reports experimental studies of the development of bulk optical properties as a function of crystallite size for the inorganic direct gap semiconductor CdS. Small crystallites are synthesized via colloidal chemical techniques, and their optical properties are studied in situ at extreme dilution. The crystallites are characterized via high resolution transmission electron microscopy. Direct images show (111) lattice planes, and establish the crystallite structures as close to those of excised fragments of bulk CdS (zinc‐blende cubic). Large crystallites (> 100 A average diameter) show an optical absorption, in colloidal solution, close to that of bulk crystalline material. However, small crystallites of 30 A average diameter show a large blue shift (∼0.8 eV) in absorption edge (effective band gap), and an intensification of edge absorption relative to absorption at higher energy regions. These observations can be understood as quantum size effects resulting from confinement of an electron and hole in a small volume. 40 A average size crystallites show a smaller shift (∼0.25 eV), and corresponding changes in their fluorescence, and resonance Raman excitation, spectra.
636 citations
582 citations
TL;DR: In this article, the size-dependent physical and chemical properties of clusters, the methods of synthesis of macroscopic amounts of size-selected clusters with desired properties, and most importantly, the possibility of their controlled assembly into new materials with novel properties.
Abstract: The Panel was charged with assessing the present scientific understanding of the size-dependent physical and chemical properties of clusters, the methods of synthesis of macroscopic amounts of size-selected clusters with desired properties, and most importantly, the possibility of their controlled assembly into new materials with novel properties. The Panel was composed of both academic and industrial scientists from the physics, chemistry, and materials science communities, and met in January 1988.In materials (insulators, semiconductors, and metals) with strong chemical bonding, there is extensive spatial delocalization of valence electrons, and therefore the bulk physical properties which depend upon these electrons develop only gradually with cluster size. Recent research using supersonic-jet, gas-aggregation, colloidal, and chemical-synthetic methods indeed clearly establishes that intermediate size clusters have novel and hybrid properties, between the molecular and bulk solid-state limits. A scientific understanding of these transitions in properties has only been partially achieved, and the Panel believes that this interdisciplinary area of science is at the very heart of the basic nature of materials. In Sec. V (Future Challenges and Opportunities), a series of basic questions for future research are detailed. Each question has an obvious impact on our potential ability to create new materials.Present methods for the synthesis of useful amounts of size-selected clusters, with surface chemical properties purposefully controlled and/or modified, are almost nonexistent, and these fundamentally limit our ability to explore the assembly of clusters into potentially novel materials. While elegant spectroscopic and chemisorption studies of size-selected clusters have been carried out using molecular-beam technologies, there are no demonstrated methods for recovery and accumulation of such samples. Within the past year, the first reports of the chemical synthesis of clusters with surfaces chemically modified have been reported for limited classes of materials. Apparatus for the accumulation and consolidation of nanophase materials have been developed, and the first promising studies of their physical properties are appearing. In both the chemical and nanophase synthesis areas, clusters with a distribution of sizes and shapes are being studied. Progress on macroscopic synthetic methods for size-selected clusters of controlled surface properties is the most important immediate goal recognized by the Panel. Simultaneous improvement in physical characterization will be necessary to guide synthesis research.Assuming such progress will occur, the Panel suggests that self-assembly of clusters into new elemental polymorphs and new types of nanoscale heterogeneous materials offers an area of intriguing technological promise. The electrical and optical properties of such heterogeneous materials could be tailored in very specific ways. Such ideas are quite speculative at this time; their implementation critically depends upon controlled modification of cluster surfaces, and upon development of characterization and theoretical tools to guide experiments.The Panel concluded that a number of genuinely novel ideas had been enunciated, and that in its opinion some would surely lead to exciting new science and important new materials.
464 citations