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, Si-doped GaN films in polycrystalline form were deposited on quartz substrates at deposition temperatures ranging from 300-623 K using r.f. sputtering technique.
Abstract: Si-doped GaN films in polycrystalline form were deposited on quartz substrates at deposition temperatures ranging from 300–623 K using r.f. sputtering technique. Electrical, optical and microstructural properties were studied for these films. It was observed that films deposited at room temperature contained mainly hexagonal gallium nitride (h-GaN) while films deposited at 623 K were predominantly cubic (c-GaN) in nature. The films deposited at intermediate temperatures were found to contain both the hexagonal and cubic phases of GaN. Studies on the variation of conductivity with temperature indicated Mott’s hopping for films containing c-GaN while Efros and Shklovskii (E-S) hopping within the Coulomb gap was found to dominate the carrier transport mechanism in the films containing h-GaN. A crossover from Mott’s hopping to E-S hopping in the ‘soft’ Coulomb gap was noticed with lowering of temperature for films containing mixed phases of GaN. The relative intensity of the PL peak at ∼2·73 eV to that for peak at ∼3·11 eV appearing due to transitions from deep donor to valence band or shallow acceptors decreased significantly at higher temperature. Variation of band gap showed a bowing behaviour with the amount of cubic phase present in the films.
6 citations
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...Now, for the ES hopping model to be applicable in these GaN films, the following criteria are to be satisfied (Pal et al 1994; Mandal et al 1999) (i) Wopt ≥ kT or T0 ≥ T; (ii) Ropt ≥ d and (iii) Δ > Wopt, Δ >> kT. (26) It appears from the values of the different parameters evaluated for our films…...
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TL;DR: In this article, a multi-target magnetron sputtering system was used to deposit SiO 2 /CdTe/SiO 2 composite films in the nanocrystalline form onto fused silica substrates at a system pressure ∼15 Pa.
Abstract: SiO 2 /CdTe/SiO 2 composite films in the nanocrystalline form were deposited using a multi-target magnetron sputtering system onto fused silica substrates at a system pressure ∼15 Pa. Different sets of nanocomposite films with different ratios of the sizes of the nanocrystallites ( d ) and intercrystallite distances ( s ) were deposited by changing the relative time of sputtering during sequential sputtering of the targets. The films were characterized by measuring optical, electrical and microstructural properties. Variation of electrical conductivity with temperature indicated Efros hopping within the Coulomb gap to be the predominant carrier transport process in these composite films. A crossover from ‘soft’ to ‘hard’ Coulomb gap was observed with lowering of film temperature. Photoluminescence measurements were carried out in the temperature range 80–300 K. The experimental results were compared with those calculated from the empirical relations regarding the temperature dependence of band-edge energy.
6 citations
TL;DR: In this paper, the results of SEM and XRD studies, optical absorption spectra and photoluminescence emission spectra are presented for the films of (Cd0.95-Pb0.05)S:CdCl2, Gd/Dy prepared by chemical bath deposition technique and using thiophenol and methanol as capping agents.
Abstract: Results of SEM and XRD studies, optical absorption spectra and photoluminescence emission spectra are presented for the films of (Cd0.95-Pb0.05)S:CdCl2, Gd/Dy prepared by chemical bath deposition technique and using thiophenol and methanol as capping agents. The deposition of films is based on precipitation followed by condensation on the substrates. SEM studies show existence of irregular distribution of particles alongwith presence of rod/tube type structure. The XRD studies show diffraction lines of CdS, PbS and CdCl2. Blue shift has been observed in absorption spectra showing quantum confinement. Particle sizes determined from XRD studies and absorption spectral studies are found to lie in the nano range. Photoluminescence emission spectra consist of emissions in blue and green-yellow regions. The observed emissions are related to the combination of defect levels and levels due to rare earths. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
3 citations
TL;DR: In this article, a simulation procedure for fitting the determined absorption edges of these layers is introduced, which leads to particle size distribution functions showing an increasing broadening with increasing layer thickness, and the distribution maximum is moving to larger crystallite radii with larger film thickness.
Abstract: Nanocrystalline ZnS thin layers are prepared by ion layer gas reaction, a low cost deposition method for compound semiconductor thin films. They are investigated by optical spectroscopy, x-ray fluorescence and energy dispersive x-ray analysis. It is seen that the absorption edges are shifting towards lower photon energies with increasing layer thickness. Also, the amount of unconverted precursor salt is decreased. A simulation procedure for fitting the determined absorption edges of these layers is introduced. This leads to particle size distribution functions showing an increasing broadening with increasing layer thickness. Moreover, the distribution maximum is moving to larger crystallite radii with larger film thickness. Both results indicate a growth in crystallite size during the layer deposition. Additionally, the increase in strength of the phonon-photon-coupling confirms the conclusions of transmission electron micrographs. Later investigations show that the noncrystalline precursor matrix which s...
2 citations
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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