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H.A. Zayed

Bio: H.A. Zayed is an academic researcher from Ain Shams University. The author has contributed to research in topics: Thin film & Band gap. The author has an hindex of 9, co-authored 11 publications receiving 207 citations.

Papers
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Journal ArticleDOI
M.A. Kenawy1, A. F. El-Shazly1, M. A. Afifi1, H.A. Zayed1, H. A. El-Zahid1 
TL;DR: In this article, the electrical and switching properties of InSe thin films have been studied and it was found that the dark electrical resistivity decreases with an increase in film thickness and temperature.

47 citations

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TL;DR: In this paper, the lattice constants, grain size, microstrain and dislocation density were studied by using X-ray diffraction in the wavelength range 400-2500nm.

34 citations

Journal ArticleDOI
TL;DR: In this article, the optical transmission and reflection at normal incidence of amorphous Sb x Se 1− x (0⩽ x ⩽ 0.9) thin films of different thickness (from 40 to 320 nm) were measured at room temperature in the wavelength region 500-1300 nm.

26 citations

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TL;DR: In this paper, photochromic coatings of molybdenum oxide films were deposited on glass substrates by spray pyrolysis technique and the surface topography was characterized by atomic force microscopy roughness data and particle size histograms.

21 citations

Journal ArticleDOI
M. A. Redwan1, E. H. Aly1, L. I. Soliman, A. A. El-Shazely1, H.A. Zayed1 
24 Jan 2003-Vacuum
TL;DR: In this article, the effect of heat treatment with or without CdCl 2 enhances the grain size and improves the crystallinity of the CdTe thin films and the activation energy decreases.

21 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, it is explained phenomenologically in terms of the "doping pinning rule" that semiconductors differ widely in their ability to be doped as their band gap increases and it is usually possible to dope them either n or p type, but not both.
Abstract: Semiconductors differ widely in their ability to be doped As their band gap increases, it is usually possible to dope them either n or p type, but not both This asymmetry is documented here, and explained phenomenologically in terms of the “doping pinning rule”

424 citations

Journal ArticleDOI
TL;DR: In this article, a review of the materials aspects of CdTe/CdS solar cells for solar energy conversion is presented, focusing on fundamental and critical aspects like: (a) choice of window layer and absorber layer; (b) drawbacks associated with the device including environmental problems, optical absorption losses and back contact barriers; (c) structural dynamics at CdS-CdTe interface; (d) influence of junction activation process by CdCl2 or HCF2Cl treatment; (e) interface and grain boundary passivation effects; (f
Abstract: Among the armoury of photovoltaic materials, thin film heterojunction photovoltaics continue to be a promising candidate for solar energy conversion delivering a vast scope in terms of device design and fabrication. Their production does not require expensive semiconductor substrates and high temperature device processing, which allows reduced cost per unit area while maintaining reasonable efficiency. In this regard, superstrate CdTe/CdS solar cells are extensively investigated because of their suitable bandgap alignments, cost effective methods of production at large scales and stability against proton/electron irradiation. The conversion efficiencies in the range of 6–20% are achieved by structuring the device by varying the absorber/window layer thickness, junction activation/annealing steps, with more suitable front/back contacts, preparation techniques, doping with foreign ions, etc. This review focuses on fundamental and critical aspects like: (a) choice of CdS window layer and CdTe absorber layer; (b) drawbacks associated with the device including environmental problems, optical absorption losses and back contact barriers; (c) structural dynamics at CdS–CdTe interface; (d) influence of junction activation process by CdCl2 or HCF2Cl treatment; (e) interface and grain boundary passivation effects; (f) device degradation due to impurity diffusion and stress; (g) fabrication with suitable front and back contacts; (h) chemical processes occurring at various interfaces; (i) strategies and modifications developed to improve their efficiency. The complexity involved in understanding the multiple aspects of tuning the solar cell efficiency is reviewed in detail by considering the individual contribution from each component of the device. It is expected that this review article will enrich the materials aspects of CdTe/CdS devices for solar energy conversion and stimulate further innovative research interest on this intriguing topic.

333 citations

Journal ArticleDOI
Shufen Wang1, Weiren Fan1, Zichuan Liu1, Aibing Yu1, Xuchuan Jiang1 
TL;DR: Wang et al. as discussed by the authors summarized recent progress in different advanced strategies to improve WO3 photochromic properties, such as a fast photoresponse (within 1 min), strong and stable photochromism, visible-light coloration and reversible photo chromism.
Abstract: Photochromic materials have been extensively studied because they are quite attractive and promising for many applications. Tungsten oxide (WO3), a typical photochromic material, has attracted considerable attention. So far, many advances have been achieved in different subfields of WO3 photochromism, mainly focused on the enhancement of WO3 photochromic properties, which depends not only on the chemical features but also on the microstructures, interface and hybrid components. This review aims to summarize recent progress in different advanced strategies to improve WO3 photochromic properties, such as a fast photoresponse (within 1 min), strong and stable photochromism, visible-light coloration and reversible photochromism. However, it is still challenging to achieve these properties for large-scale commercial applications. In addition, many previous studies have been limited to lab research purposes, although some photochromic WO3-based devices have been fabricated. To address the above-mentioned issues clearly, this review will provide a discussion of the following aspects. First, the fundamental photochromism of WO3 is described. Secondly, various advances towards improving its photochromic properties will be summarized. Thirdly, the optical applications of WO3-based photochromic materials will be reviewed and discussed. And finally, a perspective on the development trends in WO3-based photochromic materials and devices is proposed.

193 citations

Journal ArticleDOI
01 Apr 1994-Vacuum
TL;DR: In this article, the currentvoltage characteristic in the OFF-state and switching phenomenon in Ge 20 M 75 Bi 5 (M  S, Se or Te) chalcogenide semiconductor thin films was investigated.

124 citations

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TL;DR: In this paper, the thermal properties of the amorphous and crystalline state of phase-change materials are investigated and it is shown that higher thermal displacements and a more pronounced anharmonic behavior in the crystalline phase are related to the change of bonding upon crystallization, which leads to an increase of the sound velocity and a softening of the optical phonon modes at the same time.
Abstract: Crystallization of an amorphous solid is usually accompanied by a signifi cant change of transport properties, such as an increase in thermal and electrical conductivity. This fact underlines the importance of crystalline order for the transport of charge and heat. Phase-change materials, however, reveal a remarkably low thermal conductivity in the crystalline state. The small change in this conductivity upon crystallization points to unique lattice properties. The present investigation reveals that the thermal properties of the amorphous and crystalline state of phase-change materials show remarkable differences such as higher thermal displacements and a more pronounced anharmonic behavior in the crystalline phase. These fi ndings are related to the change of bonding upon crystallization, which leads to an increase of the sound velocity and a softening of the optical phonon modes at the same time.

122 citations