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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TL;DR: In this article, the conduction mechanism is dominated by the combined effects of thermionic emission, tunneling, and variable range hopping, and it is observed that conduction properties of these nano CdS films in dark and when illuminated is measured.
Abstract: Nanostructured CdS films are deposited by the high pressure magnetron sputtering technique onto glass and NaCl substrates at various substrate temperatures and at a fixed gas pressure. Electrical conductivity of these nano CdS films in dark and when illuminated is measured. It is observed that the conduction mechanism is dominated by the combined effects of thermionic emission, tunneling, and variable range hopping.
14 citations
TL;DR: In this paper, electrical properties of nanostructured ZnSe films deposited onto quartz substrates by high pressure (~20 Pa) d.c. magnetron sputtering technique were studied.
Abstract: Electrical properties of nanostructured ZnSe films deposited onto quartz substrates by high pressure (~20 Pa) d.c. magnetron sputtering technique were studied. The grain size varied within 4 to 4.4 nm with variation of deposition temperature (Ts) from 233 to 273 K. The variation of the electrical conductivity (σ) with temperature was measured in the temperature range of 120–240 K. The conductivity showed ( T 0 T ) p dependence with variation of p within 0.4 to 0.6 indicating the presence of a Coulomb gap (~0.03 eV) near the Fermi level. Efros-Shklovskii hopping (with average p = 0.5) was predominant at low temperature which changed to Mott's hopping with increasing temperature. The existing theoretical models were used to determine the range of hopping energy (0.027 to 0.037 eV) and hopping distance (4.2 to 5.8 nm) in nanocrystalline ZnSe films. Applicability of the percolation model was tested. The effective potential barrier offered by the intergrannular insulating region was found to increase from 0.004 to 0.094 eV with the decrease of grain size from 4.43 to 3.98 nm.
14 citations
01 Jan 2009
TL;DR: In this article, the optical and microstructural properties of nanocrystalline GaN films were studied at different substrate temperatures (210-300 K) and showed a reduction in size of the nanoparticles.
Abstract: Nanocrystalline GaN films were prepared by high pressure (∼ 25 Pa) rf sputtering technique onto quartz and NaCl substrates. The optical and microstructural properties of these films deposited at different substrate temperatures (210-300 K) have been studied. The films deposited at lower substrate temperature showed a reduction in size of the nanoparticles. The observed blue shift of the band gap due to reduction in crystallite size is correlated with transmission electron microscopy observation. The films showed a mixed phase (cubic and hexagonal) to coexist. The optical absorption in these films could be explained by the combined contribution from inhomogeneity and phonon broadening effect along with optical loss due to light scattering at the nanocrystallites. The photoluminescence peak positions depended on the surface to volume ratio of the films.
13 citations
TL;DR: In this article, the electrical conductivities of ZnS0.05Se0.95 nanocrystalline films were measured in the temperature range of 180-300 K. It was observed that the low temperature conductivity could be explained by hopping of the charge carriers in the Coulomb gap while at elevated temperature Mott hopping is the predominant mode of conduction in these films.
Abstract: ZnS0.05Se0.95 nanocrystalline films were deposited onto fused silica and GaAs (100) substrates by the magnetron sputtering technique. The electrical conductivities of the films deposited onto fused silica substrates were measured in the temperature range of 180–300 K. It was observed that the low temperature conductivity could be explained by hopping of the charge carriers in the Coulomb gap while at elevated temperature Mott hopping is the predominant mode of conduction in these films. A distinct cross over from Efros–Shklovoskii to Mott hopping is observed for all the films. Optical spectra were found to be dominated by the combined effects of optical losses due to absorption and scattering. The absorption spectra indicated a blueshift, the extent of which depended on the crystallite size.
12 citations
TL;DR: In this article, SiO2/CdSe/SiO2 composite films in nanocrystalline form were deposited on quartz substrates at ∼20 Pa with deposition temperatures ranging from 220 to 240 K using a multi-target magnetron sputtering system.
Abstract: SiO2/CdSe/SiO2 composite films in nanocrystalline form were deposited on quartz substrates at ∼20 Pa with deposition temperatures ranging from 220 to 240 K using a multi-target magnetron sputtering system. Optical, electrical, and microstructural (TEM and AFM) studies were carried out on the composite films. Studies of the variation of conductivity with temperature indicated Efros hopping within the Coulomb gap to be the predominant carrier transport process in the composite films. Furthermore, a crossover from a ‘soft’ to a ‘hard’ Coulomb gap was noticed with lowering of temperature.
11 citations
References
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Book•
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01 Jan 1959
TL;DR: In this paper, the authors discuss various topics about optics, such as geometrical theories, image forming instruments, and optics of metals and crystals, including interference, interferometers, and diffraction.
Abstract: The book is comprised of 15 chapters that discuss various topics about optics, such as geometrical theories, image forming instruments, and optics of metals and crystals. The text covers the elements of the theories of interference, interferometers, and diffraction. The book tackles several behaviors of light, including its diffraction when exposed to ultrasonic waves.
19,815 citations
[...]
01 Oct 1999
TL;DR: In this article, the authors discuss various topics about optics, such as geometrical theories, image forming instruments, and optics of metals and crystals, including interference, interferometers, and diffraction.
Abstract: The book is comprised of 15 chapters that discuss various topics about optics, such as geometrical theories, image forming instruments, and optics of metals and crystals. The text covers the elements of the theories of interference, interferometers, and diffraction. The book tackles several behaviors of light, including its diffraction when exposed to ultrasonic waves.
19,503 citations
2,822 citations
TL;DR: In this article, an extensive numerical calculation for the eigenvalue problem is carried out by Ritz's variational technique, and the motional state of the lowest level is classified into three regimes: the regime of exciton confinement for R/${a}_{B}^{\mathrm{*}}$\ensuremath{\gtrsim}4, the regime for individual particle confinement forR/${b}^{*}+1.2.
Abstract: Quantum-size effects of an electron-hole system confined in microcrystals of semiconductors are studied theoretically with the spherical-dielectric continuum model. An extensive numerical calculation for the eigenvalue problem is carried out by Ritz's variational technique. The motional state of the lowest level is classified into three regimes: the regime of exciton confinement for R/${a}_{B}^{\mathrm{*}}$\ensuremath{\gtrsim}4, the regime of individual particle confinement for R/${a}_{B}^{\mathrm{*}}$\ensuremath{\lesssim}2, and the intermediate regime for 2\ensuremath{\lesssim}R/${a}_{B}^{\mathrm{*}}$\ensuremath{\lesssim}4, where R is the radius of the quantum well and ${a}_{B}^{\mathrm{*}}$ is the exciton Bohr radius. In the region R/${a}_{B}^{\mathrm{*}}$\ensuremath{\gtrsim}4, the high-energy shift of the lowest exciton state is described by the rigid-sphere model of the exciton quite well, which takes into account the spatial extension of the relative motion of the electron and the hole. The oscillator strength of the interband optical transition changes dramatically across the region 2\ensuremath{\lesssim}R/${a}_{B}^{\mathrm{*}}$\ensuremath{\lesssim}4. The metamorphosis of the absorption spectrum is shown as a function of R/${a}_{B}^{\mathrm{*}}$ and compared with the experimental data.
1,119 citations
AT&T1
TL;DR: In this paper, a review and analysis of the optical properties of quantum crystallites, with principal emphasis on the electro-optic Stark effect and all optical third order nonlinearity is presented.
Abstract: This is a review and analysis of the optical properties of quantum crystallites, with principal emphasis on the electro-optic Stark effect and all optical third order nonlinearity. There are also introductory discussions on physical size regimes, crystallite synthesis, quantum confinement theory, and linear optical properties. The experiments describe CdSe crystallites, exhibiting strong confinement of electrons and holes, and CuCl crystallites, exhibiting weak confinement of the exciton center of mass. In the CdSe system, neither the Stark effect nor the third order nonlinearity is well understood. The Stark shifts appear to be smaller than calculated, and field inducted broadening also occurs. The third order nonlinearity is only modestly stronger than in bulk material, despite theoretical prediction. Unexpectedly large homogeneous widths, due to surface carrier trapping, in the nominally discrete crystallite excited states appear to be involved. The CuCl system shows far narrower spectroscopic homogeneous widths, and corresponds more closely to an ideal quantum dot in the weak confinement limit. CuCl also exhibits exciton superradiance at low temperature. Surface chemistry and crystallite encapsulation are critical in achieving the predicted large Stark and third order optical effects in II-VI and III-V crystallites.
995 citations