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The optical and electrical properties of n-type chlorine-doped Sb2Se3 single crystals, with free carrier concentrations above 1016 cm−3 at room temperature, have been studied. The experiments reveal a strongly polarized temperature-dependent long-wavelength infrared absorption attributable to conduction band electrons within the material. For wavelengths between 1.6 and 6 μm, the room temperature absorption varies as λ 2.5 ± 0.3 , suggesting that longitudinal optical mode scattering is the dominant electron scattering mechanism. The results are most consistent with the hypothesis that electron transport in Sb2Se3 is band-like and not intrinsically limited by small-polaron self-trapping. [ABSTRACT FROM AUTHOR]

The optical and electrical properties of n-type chlorine-doped Sb2Se3 single crystals, with free carrier concentrations above 1016 cm−3 at room temperature, have been studied. The experiments reveal a strongly polarized temperature-dependent long-wavelength infrared absorption attributable to conduction band electrons within the material. For wavelengths between 1.6 and 6 μm, the room temperature absorption varies as λ 2.5 ± 0.3 , suggesting that longitudinal optical mode scattering is the dominant electron scattering mechanism. The results are most consistent with the hypothesis that electron transport in Sb2Se3 is band-like and not intrinsically limited by small-polaron self-trapping. [ABSTRACT FROM AUTHOR]

This study introduces a method for creating Ohmic contacts to tin oxide (SnO2) by subjecting the sample surface to hydrogen plasma treatment at moderate temperatures of about 300 °C. This process generates a surface layer of metallic tin droplets, forming suitable electrical contacts. The contacts exhibit remarkable durability and demonstrate Ohmic behavior down to liquid helium temperatures. [ABSTRACT FROM AUTHOR]

Titanium dioxide ( TiO 2 , also known as titania) has attracted a great deal of attention since the discovery of photocatalytic splitting of water under ultraviolet light exposure by Fujishima and Honda. Three modifications of TiO 2 are known to occur in nature: rutile, brookite, and anatase, of which only the first is a stable polymorph of bulk titania. The contribution of the surface free energy, however, makes anatase a stable polymorph at the nanometer scale. Compared to rutile, anatase has a longer carrier lifetime and exciton diffusion length, higher electron mobility, and is an order of magnitude more efficient in photocatalysis, which makes it a material of choice for a variety of applications. Hydrogen is a common impurity in TiO 2 with a strong impact on its electrical and optical properties. In this Perspective, we discuss the application of IR absorption, Raman scattering, electron paramagnetic resonance, and ab initio theory to get insight into the properties of hydrogen in bulk single-crystalline anatase. In particular, interstitial hydrogen, hydrogen substituting for oxygen, the nature of "hidden" species, as well as complexes formed by hydrogen with acceptors are considered. [ABSTRACT FROM AUTHOR]

A study combining vibrational spectroscopy and first-principles theory is presented for a hydrogen-related defect in natural anatase TiO 2 that is characterized by an O–H vibrational mode at 3373 cm − 1 (10 K). Based on complementary Raman scattering, IR absorption, electron paramagnetic resonance, and secondary ion mass spectrometry data supported also by ab initio calculations, it is tentatively proposed that the defect responsible for the 3373 cm − 1 line includes two hydroxyl units located next to a substitutional iron atom, Fe Ti H 2. The defect may exist in at least two charge states, whereby the 3373 cm − 1 line is associated with the positive charge state of the complex. [ABSTRACT FROM AUTHOR]

The impact of hydrogen in ZnO is revealed by combining reaction dynamics calculations with temperature dependent Hall (TDH), photoluminescence, and secondary ion mass spectrometry measurements performed on H, 2 H, and He implanted ZnO. H and 2 H box profiles with a concentration ranging from ∼ 3 × 10 17 cm − 3 to ∼ 10 19 cm − 3 and He to produce as much as damage as in the [H] ∼ 3 × 10 17 cm − 3 case were implanted in the samples. The formation of Li lean regions has been observed for [ 2 H] < 10 19 cm − 3 after annealing at 400 ° C. This is attributed to Li i presence consequent to the diffusion of Zn i created during the H/ 2 H implantation process. Results extracted from the TDH measurements performed prior to the annealing at 400 ° C evidence that Li i contributes to an increase in carrier concentration up to ∼ 10 17 cm − 3 by providing a donor level with an activation energy of ∼ 40 meV and thus is very close to the value of ∼ 47 meV expected for H in the oxygen site. The reaction dynamics analysis evidences that the amount of Li i introduced is decreasing at higher H implantation doses as a result of increasing V Zn and H-V Zn retrapping, reactions in which Li i is competing with H. Overall, due to Li i formation as well as the presence of Al the maximum percentage of the implanted H or 2 H acting as a donor in the investigated range is found to be ≲ 2%, which is considerably lower than previously reported. [ABSTRACT FROM AUTHOR]

The method of photoconductive detection of defect-related vibrational modes in semiconductors by Fano resonances is validated by a combined photoconductivity and infrared absorption study of the interstitial hydrogen donor in ZnO. Depth-resolved isotopic substitution experiments with varying concentrations of H and D show that the effect of vibrational mode-related absorption has to be taken into account in order to allow for an unambiguous interpretation of the experimental data. A quantitative model is presented which describes the influence of sample thickness, defect concentration, and the presence of other donors on the sign, magnitude, and shape of the Fano resonances. Implications for the photoconductive detection of defect-related vibrational modes are discussed. [ABSTRACT FROM AUTHOR]

Electronic states in the upper part of the bandgap of reduced and/or hydrogenated n-type rutile TiO2 single crystals have been studied by means of thermal admittance and deep-level transient spectroscopy measurements. The studies were performed at sample temperatures between 28 and 300 K. The results reveal limited charge carrier freeze-out even at 28 K and evidence the existence of dominant shallow donors with ionization energies below 25 meV. Interstitial atomic hydrogen is considered to be a major contributor to these shallow donors, substantiated by infrared absorption measurements. Three defect energy levels with positions of about 70 meV, 95 meV, and 120 meV below the conduction band edge occur in all the studied samples, irrespective of the sample production batch and the post-growth heat treatment used. The origin of these levels is discussed in terms of electron polarons, intrinsic point defects, and/or common residual impurities, where especially interstitial titanium atoms, oxygen vacancies, and complexes involving Al atoms appear as likely candidates. In contrast, no common deep-level defect, exhibiting a charge state transition in the 200–700 meV range below the conduction band edge, is found in different samples. This may possibly indicate a strong influence on deep-level defects by the post-growth heat treatments employed. [ABSTRACT FROM AUTHOR]

Hydrogen donors in ZnO and rutile TiO2 are probed by means of photoconductivity and IR absorption. It is shown that the O-H bonds giving rise to the local vibrational modes (LVMs) of interstitial hydrogen at 3611 and 3290 cm-1 in the case of ZnO and TiO2, respectively, also occur in the photoconductivity spectra as Fano resonances. The effects of isotope substitution, concentration, sample thickness, influence of other donors present in both oxides are considered. Based on the shape and frequency of these resonances, it is concluded that the apparent ionization energy of interstitial hydrogen in rutile TiO2 is less than 300meV. By a direct comparison, we also demonstrate that photoconductive detection of LVMs of defects in thin semiconductor films is superior to the standard IR absorption. [ABSTRACT FROM AUTHOR]

The diffusion and dissociation mechanisms governing the evolution of oxygen and vacancyoxygen defects in Czochralski-grown Si samples have been studied. The samples were irradiated at (i) room temperature or (ii) elevated temperature (350 °C) by MeV electrons and then isothermally annealed at 8 different temperatures in the range of 300 °C to 500 °C. The evolution of the concentrations of oxygen complexes (On, n≤3) and mono-vacancy-oxygen defects (VOn, n≤4) have been followed by infrared absorption measurements of local vibrational modes originating from the individual defects. The experimental kinetics data have been compared with simulation results based on the theory for diffusion limited reactions, assuming a model where sequential build-up of the VOn defects is a key ingredient. A close quantitative agreement is obtained for both sets of samples despite quite different initial conditions prior to the annealing, which adds evidence to the validity of the model. Values for the diffusivity and dissociation rates of VOn (n≤4) and On (n≤3) have been deduced and in general, the mobility and stability of VOn decrease and increase with n, respectively. For all the defects, partial dissociation appears as a prevailing process during diffusion, while full dissociation of VOn is limited by an energy barrier identical to that of interstitial oxygen (Oi) diffusion (~2.55 eV). The oxygen dimer and trimer are fast diffusers but slower than substitutional oxygen, i.e., VO; VO is found to be the most mobile species, whilst Oi is the slowest one with a difference in diffusivity of up to 7 orders of magnitude in the studied temperature range. [ABSTRACT FROM AUTHOR]

Hydrogen defects in single-crystalline SnO2 are studied by combined photoconductivity and IR absorption spectroscopy. Our results indicate that a defect with an O–H local vibrational mode at 3272 cm−1 (10 K) is a donor with a level less than 300 meV below the conduction band. Annealing experiments demonstrate that the defect is stable up to approximately 450 °C and therefore may contribute to persistent n-type conductivity of SnO2. [ABSTRACT FROM AUTHOR]

Hydrogen defects in single-crystalline SnO2 are studied by combined photoconductivity and IR absorption spectroscopy. Our results indicate that a defect with an O–H local vibrational mode at 3272 cm−1 (10 K) is a donor with a level less than 300 meV below the conduction band. Annealing experiments demonstrate that the defect is stable up to approximately 450 °C and therefore may contribute to persistent n-type conductivity of SnO2. [ABSTRACT FROM AUTHOR]

Titanium dioxide ( TiO 2 , also known as titania) has attracted a great deal of attention since the discovery of photocatalytic splitting of water under ultraviolet light exposure by Fujishima and Honda. Three modifications of TiO 2 are known to occur in nature: rutile, brookite, and anatase, of which only the first is a stable polymorph of bulk titania. The contribution of the surface free energy, however, makes anatase a stable polymorph at the nanometer scale. Compared to rutile, anatase has a longer carrier lifetime and exciton diffusion length, higher electron mobility, and is an order of magnitude more efficient in photocatalysis, which makes it a material of choice for a variety of applications. Hydrogen is a common impurity in TiO 2 with a strong impact on its electrical and optical properties. In this Perspective, we discuss the application of IR absorption, Raman scattering, electron paramagnetic resonance, and ab initio theory to get insight into the properties of hydrogen in bulk single-crystalline anatase. In particular, interstitial hydrogen, hydrogen substituting for oxygen, the nature of "hidden" species, as well as complexes formed by hydrogen with acceptors are considered. [ABSTRACT FROM AUTHOR]

A study combining vibrational spectroscopy and first-principles theory is presented for a hydrogen-related defect in natural anatase TiO 2 that is characterized by an O–H vibrational mode at 3373 cm − 1 (10 K). Based on complementary Raman scattering, IR absorption, electron paramagnetic resonance, and secondary ion mass spectrometry data supported also by ab initio calculations, it is tentatively proposed that the defect responsible for the 3373 cm − 1 line includes two hydroxyl units located next to a substitutional iron atom, Fe Ti H 2. The defect may exist in at least two charge states, whereby the 3373 cm − 1 line is associated with the positive charge state of the complex. [ABSTRACT FROM AUTHOR]

The annealing behavior of the center in ZnO, which leads to a local vibrational mode at , has been studied. Infrared absorption measurements confirm the previous findings that the center dissociates already at temperatures higher than about 500C and an apparent stability up to 1250C is due to efficient retrapping of H by Li. Secondary ion mass spectrometry data indicate that Fe impurities prevent a reformation of after dissociation. The formation of Fe −Li complexes is proposed as a prevailing mechanism for this behavior. [ABSTRACT FROM AUTHOR]

Interstitial hydrogen in rutile TiO2 is studied by infrared (IR) absorption. The measurements identify this defect as a shallow donor with an ionization energy of 10 ± 1 meV. The IR absorption lines at around 3290 cm-1 include local vibrational modes (LVMs) of the neutral and the positive charge states of the donor. The neutral charge state reveals two LVMs at 3288.3 and 3292.0 cm-1, whereas the positive charge state has a vibrational mode at 3287.4 cm-1. [ABSTRACT FROM AUTHOR]