Transient Photoconductivity in GaAs Films Grown by Molecular Beam Epitaxy.

1989 ◽  
Vol 145 ◽  
Author(s):  
A. Werner ◽  
T. D. Moustakas ◽  
M. Kunst

AbstractHahn-Meitner-Institut, D-1000 Berlin 39, W. Germany Abstract The transient photoconductivity, in MBE grown silicon doped GaAs films, was studied by a contactless microwave conductivity technique. The dark carrier concentration of the investigated films varies from 4 x 1014 cm-3 to 6 x 1017 cm-3. At least two decay channels can be distinguished. An initial fast decay process (t<20 ns), which is excitation intensity dependent, followed by a slower one. The fast decay is tentativly identified with a direct electron-hole recombination and is more pronounced at high excitation intensities and in low impurity materials. The slower decay component is characterized by effective electron lifetimes ranging from 2 µs for low impurity fims up to 100 µs for high impurity samples. It can be concluded that an increase of the Si-concentration leads to an increase in the concentration of hole traps, which quenches the initial electron-hole recombination and decreases the electron decay rate in the microsecond region.

1993 ◽  
Vol 297 ◽  
Author(s):  
M. Kunst ◽  
C. Haffer ◽  
C. Swiatkowski

Excess electron-hole recombination at high excitation densities in a-Si:H is investigated by comparison of the transient photoconductivity during and just after excitation in the nanosecond time range to numerical models. A simple one parameter recombination model fits the experimental data satisfactorily. An extension of the model where deep trapping is taken into account explains also the transient photoconductivity in Boron doped a-Si:H.


2014 ◽  
Vol 13 (05) ◽  
pp. 1450034 ◽  
Author(s):  
Yong-Qiang Zhang ◽  
Xiao-Hui Li ◽  
Fen-Fen Li ◽  
Jie Lv ◽  
Guang-Jun Liu ◽  
...  

The layered structural model was proposed to study the geometry and electronic properties of the ( WO 3)x/( TiO 2)y heterostructures in this paper. The geometry and electronic properties were affected greatly by the relative proportion of TiO 2 and WO 3 in the nanocomposites. The minimum band gap of ( WO 3)x/( TiO 2)y heterostructures decreased with the proportion of WO 3 increasing but increased with the proportion of TiO 2 increasing. Interestingly, electrons at the upper valence band (VB) can be directly excited from 2p and 3d orbitals of titania to the conduction band (CB), which was mainly consisted of 5d orbitals of tungsten trioxide. The effective electron mass of ( WO 3)x/( TiO 2)y heterostructures was higher than that of pure TiO 2. It indicated that the electron–hole recombination rate of hybrid ( WO 3)x/( TiO 2)y heterostructure was lower than that of pure TiO 2, which might imply that photocatalytic activities of the hybrid ( WO 3)x/( TiO 2)y heterostructures were enhanced under visible light irradiation. The theoretical results might offer a new useful guide for designing semiconductors photocatalyst, such as heterostructure nanocomposites.


1998 ◽  
Vol 536 ◽  
Author(s):  
H. Porteanu ◽  
A. Glozman ◽  
E. Lifshitz ◽  
A. Eychmüller ◽  
H. Weller

AbstractCdS/HgS/CdS nanoparticles consist of a CdS core, epitaxially covered by one or two monolayers of HgS and additional cladding layers of CdS. The present paper describes our efforts to identify the influence of CdS/HgS/CdS interfaces on the localization of the photogenerated carriers deduced from the magneto-optical properties of the materials. These were investigated by the utilization of optically detected magnetic resonance (ODMR) and double-beam photoluminescence spectroscopy. A photoluminescence (PL) spectrum of the studied material, consists of a dominant exciton located at the HgS layer, and additional non-excitonic band, presumably corresponding to the recombination of trapped carriers at the interface. The latter band can be attenuated using an additional red excitation. The ODMR measurements show the existence of two kinds of electron-hole recombination. These electron-hole pairs maybe trapped either at a twin packing of a CdS/HgS interface, or at an edge dislocation of an epitaxial HgS or a CdS cladding layer.


1999 ◽  
Vol 40 (4-5) ◽  
pp. 123-130 ◽  
Author(s):  
S. Malato ◽  
J. Blanco ◽  
C. Richter ◽  
B. Milow ◽  
M. I. Maldonado

Particulate suspensions of TiO2 irradiated with natural solar tight in a large experimental plant catalyse the oxidation of organic contaminants. The problem in using TiO2 as a photocatalyst is electron/hole recombination. One strategy for inhibiting e−/h+ recombination is to add other (irreversible) electron acceptors to the reaction. In many highly toxic waste waters where degradation of organic pollutants is the major concern, the addition of an inorganic anion to enhance the organic degradation rate may be justified. For better results, these additives should fulfil the following criteria: dissociate into harmless by-products and lead to the formation of ·OH or other oxidising agents. In this paper, we attempt to demonstrate the optimum conditions for the treatment of commercial pesticide rinsates found in the wastewater produced by a pesticide container recycling plant. The experiments were performed in one of the pilot plants of the largest solar photocatalytic system in Europe, the Detoxification Plants of the Plataforma Solar de Almería (PSA), in Spain. After testing ten different commercial pesticides, results show that peroxydisulphate enhances the photocatalytic miniralization of all of them. This study is part of an extensive project focused on the design of a solar photocatalytic plant for decontamination of agricultural rinsates in Almería (Spain).


RSC Advances ◽  
2014 ◽  
Vol 4 (107) ◽  
pp. 62423-62429 ◽  
Author(s):  
Sara Rahimnejad ◽  
Jing Hui He ◽  
Wei Chen ◽  
Kai Wu ◽  
Guo Qin Xu

WO3 nanoplates derived from NiWO4 were found to have the highest concentration of oxygen vacancy, narrowest band gap, longest electron–hole recombination time, and in turn the highest rate of photodegradation of azo dye methylene blue.


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