Spectrally dependent surface photovoltage measurements were performed with repetitive regime on Cu(In,Ga)S2 absorbers and on Cu(In,Ga)S2/CdS and Cu(In,Ga)S2/In2S3 junctions. The results are correlated to current-voltage investigations of the respective completed solar cells. The measurements show the presence of a space charge region in the bare Cu(In,Ga)S2 absorbers due to a high density of surface states. It is found that deposition of CdS increases the band bending whereas deposition of In2S3 does not change it.

Rutile IrO(2) is known as being among the best electrocatalysts for water oxidation. Here we report on the unexpected photocatalytic water oxidation activity of 1.98 nm ± 0.11 nm succinic acid-stabilized IrO(2) nanocrystals. From aqueous persulfate and silver nitrate solution the nonsensitized particles evolve oxygen with initial rates up to 0.96 μmol min(-1), and with a quantum efficiency of at least 0.19% (measured at 530 nm). The catalytic process is driven by visible excitations from the Ir-d(t(2g)) to the Ir-d(e(g)) band (1.5-2.75 eV) and by ultraviolet excitations from the O-p band to the Ir-d(e(g)) (>3.0 eV) band. The formation of the photogenerated charge carriers can be directly observed with surface photovoltage spectroscopy. The results shed new light on the role of IrO(2) in dye- and semiconductor-sensitized water splitting systems.

When Cu(In,Ga)(S,Se)2 is prepared by heating metal precursor films in chalcogen atmosphere (sequential process) the resulting films typically show a gradient in the Ga/(In+Ga) ratio over the depth of the film. This is generally observed for reaction periods ranging from a few minutes (rapid thermal processing) to several hours. In this work we have investigated the Ga distribution in films where the reaction period was reduced to one second. The ultra-fast reaction was achieved by passing a high electrical current through the Mo foil substrate after depositing metal and chalcogen precursors.

The porosity of electrophoretically prepared nanoporous ZnO and TiO_2 films was systematically decreased by postpressing at different pressures. The nanoporous structure of the films was fixed by sintering after the postpressing procedure. The postpressing-induced change of the internal surface area of the nanoporous films was monitored using the dye-removal technique. The effective electron diffusion coefficient ( D _eff) of the unpressed nanoporous films depended on the thickness according to Fick’s second law. When pressed, the diffusion coefficient of the films increases significantly. In nanoporous TiO_2, the increase of D _eff follows the percolation theory where transport rate depends on the particle-coordination number. In contrast to the TiO_2 films, the value of D _eff of pressed nanoporous ZnO films changed with the porosity much stronger than one would expect from the percolation theory with hard spheres. This property has been attributed to the strong increase of necking between ZnO nanoparticles with increasing pressure as indicated by a strong decrease of the internal surface area.

The electrophoretic deposition of nanoporous TiO2 layers allows us to investigate separately the influence of sintering temperature, porosity, and conformal surface coatings on the effective diffusion coefficient (Deff) of excess electrons in porous layers. Photocurrent transients were measured to obtain Deff in nanoporous TiO2 layers immersed in aqueous electrolyte. The applied treatments control parameters such as the contact between interconnected nanoparticles, the coordination of nanoparticles in the porous network, and the surface passivation of TiO2 nanoparticles. The hierarchy of the different factors for transport optimization in porous TiO2 is discussed. Under fixed geometry of the nanoporous network, trapping on surface states can strongly limit electron diffusion in porous TiO2.

Nanopores and macropores can be formed electrochemically on p‐type silicon depending on the silicon resistivity and composition of the electrolyte. In order to understand if the structural dimensionality of the porous p‐type Si, either nanopore or macropore formation, depends on the electrochemical process at the Si/electrolyte interface, in situ pulsed surface photovoltage (SPV) and photoluminescence (PL) measurements have been undertaken. The SPV and PL studies have been made as a function of the applied current density as well as the electrolyte composition (aqueous or in presence of organic solvent) and the silicon doping density. Main results show that the Si surface is well passivated with preferential formation of ionic species and the Si band bending is around 100 mV, during porous Si formation. It varies slightly with the doping density, but is not affected by the composition of the electrolyte (HF/water and HF/organic solvent). This demonstrates that the chemistry of the electrolyte plays a major role in the formation of macroporous and nanoporous Si, but has still to be determined. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electron transfer from sol–gel–prepared TiO2 into adsorbed benzene diazonium compounds has been investigated using cyclic voltammetry, x-ray photoelectron spectroscopy, contact potential difference, and surface photovoltage spectroscopy. The results show that the potential of maximum electron transfer depends strongly on the dipole moment of the benzene compound. Two reactive surface sites at which electron transfer occurs have been identified.

Electrical properties of two kinds of sandwich structures (SnO 2 :F/por-TiO 2 /Ti and Si/por-TiO 2 /Pd) are investigated by the methods of I-V, C-V characteristics and DLTS in vapors of water and alcohol. It has been demonstrated that besides the change of the conductivity and of the capacitance of the por-TiO 2 layers one can also use for gas sensing the change of the high frequency capacitance of the MOS type structure, measurement of the current response at relatively low frequencies and the modification of the charge transfer between the Si bulk and states near the por-TiO 2 /Si interface.

The changes of the band bending and of the nonradiative (nr) surface recombination are investigated by use of photovoltage and photoluminescence techniques during the electrochemical deposition of p-nitrobenzene molecules on atomically flat and rough hydrogenated as well as on chemically oxidized Si(111) surfaces. A simple and well-reproducible procedure has been developed for electrochemical grafting of organic molecules on hydrogenated Si surfaces in aqueous electrolytes. The grafting of a monolayer of p-nitrobenzene molecules on atomically flat p-Si(111):H surfaces induces a change of the band bending of about 0.1 eV and the amount of nr surface defects, Ns, is only slightly increased by a factor of about 3 (Ns<1011 cm−2) with respect to the hydrogenated Si surface. The role of the formation of radicals for the engineering of Si surfaces is discussed.

The positive oxide charge (Qox) and the concentration of nonradiative recombination defects (Nit) at a thin anodic oxide/p-Si interface are probed in situ by pulsed photovoltage and photoluminescence techniques during electron injection. Qox and Nit decreased strongly due to electron injection. The observed effect is suggested to be inverse to the negative-bias-temperature instability. Defect reactions at the anodic oxide/p-Si interface are discussed.

Microwave conductivity and Raman spectroscopy were applied to study the influence of light and thermal annealing on porous TiO2 properties. Microwave absorption in porous TiO2 (anatase) showed an anomalous behaviour in the presence of light excitation (at 514nm, i.e. below, or 356 nm, i.e. above the band Sap). Exposure to light at a time scale of minutes reduces the microwave conductivity, in contrast to many bulk semiconductors excited above band gap. A reduced content of oxygen after heating in vacuum leads also to a reduction of microwave absorption. Both observations ale in apparent contradiction with de conductivity in TiO2. By comparison with light-induced EPR experiments, we conclude that the oxygen removal creates deep defects to which are transferred electrons previously trapped in shallow donors. As a consequence, this decreases the polarisability of TiO2 nanoparticles, the microwave absorption, and the dielectric constant.

Samples of Si+ implanted in SiO2, annealed at 1150 degrees C, have an efficient photoluminescence band centered at 1.55 eV, the latter being independent from the annealing time and consequently on the Si nanocrystals' size. We measured resonantly excited photoluminescence at 1.4 K, which shows two phonon steps, shifted by 56 and 112 meV from the excitation energy, similar to porous silicon; however, with significantly different relative intensities. Based on a quantitative analysis of this measurement, on time-resolved spectroscopy and on comparison with similar measurements of direct semiconductors, we conclude that the existence of phonon replicas does not imply that the luminescence originates from quantized levels in Si nanocrystals. [S0163-1829(99)11247-5].

physica status solidi (a)Volume 167, Issue 1 p. R9-R9 ErratumFree Access Erratum to Electron Drift Mobility in Porous TiO2 (Anatase) Th. Dittrich, Th. Dittrich Physik Department E16, Technische Universität München, D-85748 Garching, GermanySearch for more papers by this authorE. A. Lebedev, E. A. Lebedev A.F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, RussiaSearch for more papers by this authorJ. Weidmann, J. Weidmann INAP GmbH, Munscheidstr. 14, D-45886 Gelsenkirchen, GermanySearch for more papers by this author Th. Dittrich, Th. Dittrich Physik Department E16, Technische Universität München, D-85748 Garching, GermanySearch for more papers by this authorE. A. Lebedev, E. A. Lebedev A.F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, RussiaSearch for more papers by this authorJ. Weidmann, J. Weidmann INAP GmbH, Munscheidstr. 14, D-45886 Gelsenkirchen, GermanySearch for more papers by this author First published: 29 January 1999 https://doi.org/10.1002/(SICI)1521-396X(199805)167:13.0.CO;2-ICitations: 4AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume167, Issue1May 1998Pages R9-R9 RelatedInformation

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The electropolishing of p-Si(100) in aqueous NH4F solution is investigated in-situ by photoluminescence (PL) with short N-2-laser pulses. The PL signal increases with potential and reaches a maximum when current oscillations occur. The PL signal oscillates with the same period but anticorrelated to the current. The thin anodic oxides are removed at a low cathodic potential. The respective peak of the current transient is used to monitor the relative changes of the anodic oxides. The results are discussed from the point of view of non-radiative defect generation during electropolishing, which is controlled by the potential and the rate of oxidation.

The electrochemical H-termination process of n-Si(111) surfaces in aqueous 0.1 M NH4F pH 4.0 solution was optimized for a two step procedure consisting of the surface smoothing during oxidation in the photocurrent oscillating potential region followed by the oxide etching and passivation of the surface atoms with hydrogen. The hydrogen termination was monitored in situ measuring the dark current transient and evaluated using pulsed surface photovoltage technique. An unusually low density of interface states it=1×1010 eV−1 cm−2 was obtained by the hydrogen termination on n-Si(111) surfaces following this procedure with better results than applying an electropolishing treatment.

The evaluation of the surface state distribution of differently HF-treated Si(111) surfaces during the native-oxide growth in air is investigated by the large-signal field-modulated photovoltage technique. The surface state distribution consisting of intrinsic and extrinsic Si dangling bond defects is directly related to the state of oxidation of the Si surface. It is shown that the kind of HF treatment strongly influences the concentration of extrinsic defects with a lower state of oxidation. Special HF preparations for H termination of the Si(111) surface result in a nearly intrinsic surface state distribution. During the oxidation process three typical phases can be distinguished each characterized by specific defect structures. It was found that native-oxide growth is highly sensitive to the concentration of extrinsic defects directly after HF treatment.

Electronic states in por-Si are investigated by the pulsed surface photovoltage technique using the por-Si/c-Si interface as probe. The values of the potentials at the por-Si/n-Si and at the por-Si/p-Si interface are -0.05 V and +0.47 V, respectively. Non-monotonous photovoltage transients related to trapping in por-Si are observed. The traps can be annealed at 150°C and generated in H20 atmosphere.