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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]

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]

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 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]

Oxygen in single crystalline antimony triselenide (Sb2Se3) is addressed by infrared (IR) absorption spectroscopy. Measurements conducted on Sb2Se3 samples doped—during growth, post-growth annealing in the O2 ambient, or by O ion implantation—with 16O reveal an IR absorption line at 527 cm−1 (10 K). Substitution of 16O by 18O "red"-shifts the signal down to 500 cm−1 based on which the line is assigned to a local vibrational mode of an isolated oxygen defect. Annealing of O-enriched samples in hydrogen atmosphere at temperatures above 380 °C results in the suppression of the 527-cm−1 line and concurrent appearance of the signals due to hydroxyl groups, suggesting formation of oxygen-hydrogen complexes. The configuration of the 527-cm−1 oxygen center is discussed. [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]

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]

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]

Recently, Timerkaeva et al. [J. Appl. Phys. 123, 161421 (2018)] reported the results of a first principles study of the di-carbon (CsCi) complex in silicon. The authors have found that CsCi may occur in four configurations labeled A, B, C, and D. The C form is claimed to have the lowest energy of all four forms. Based on this, the authors suggest that the C form was misinterpreted as the B form in some experimental studies. This comment provides arguments that the conclusions of Timerkaeva et al. [J. Appl. Phys. 123, 161421 (2018)] do not match the well-known experimental results. [ABSTRACT FROM AUTHOR]

An IR absorption study of hydrogen-related defects in natural single-crystalline anatase TiO2 has been carried out. A complex with IR absorption lines at 3412 and 3417 cm- 1 is shown to act as a donor with ionization energy of tens of meV. The two lines are identified as stretching local vibrational modes of the O-H bonds of the donor in the neutral and positive charge states, respectively. The defect is unstable against annealing at approximately 300 °C and a storage at room temperature on the time scale of a few weeks. These findings suggest that interstitial hydrogen is a plausible model of this defect. [ABSTRACT FROM AUTHOR]

IR absorption study of natural single-crystalline anatase TiO2 has been performed. It was found that as-received material reveals absorption lines at 3357.8, 3359.3, 3372.5, and 3389.3 cm−1, whose intensity grows if the sample is hydrogenated from the H2 ambient at 450 °C. In addition, hydrogenation results in the appearance of two lines at 3412.4 and 3416.9 cm−1. Isotope substitution experiments have shown that all six lines are due to the stretch local vibrational modes (LVMs) of O-H bonds, which are preferentially aligned parallel to the c-axis of TiO2. The group of LVMs at 3357.8, 3359.3, 3372.5, and 3389.3 cm−1 retains the same relative intensities and is stable against thermal treatments up to 450 °C, whereas the hydrogen-related complex(es) responsible for the 3412.4 and 3416.9 cm−1 lines disappear(s) after annealing at 250 °C. The nature of the defects resulting in these vibrational modes is discussed. [ABSTRACT FROM AUTHOR]

IR absorption study of natural single-crystalline anatase TiO2 has been performed. It was found that as-received material reveals absorption lines at 3357.8, 3359.3, 3372.5, and 3389.3 cm−1, whose intensity grows if the sample is hydrogenated from the H2 ambient at 450 °C. In addition, hydrogenation results in the appearance of two lines at 3412.4 and 3416.9 cm−1. Isotope substitution experiments have shown that all six lines are due to the stretch local vibrational modes (LVMs) of O-H bonds, which are preferentially aligned parallel to the c-axis of TiO2. The group of LVMs at 3357.8, 3359.3, 3372.5, and 3389.3 cm−1 retains the same relative intensities and is stable against thermal treatments up to 450 °C, whereas the hydrogen-related complex(es) responsible for the 3412.4 and 3416.9 cm−1 lines disappear(s) after annealing at 250 °C. The nature of the defects resulting in these vibrational modes is discussed. [ABSTRACT FROM AUTHOR]

Silicon-on-insulator wafers with thicknesses of a boron doped p-type device layer 1.5 µm to 88 nm are probed by means of photoconductive spectroscopy. It is shown that the boron acceptor manifests itself as Fano resonances at 669 and 693 cm-1 associated with the excited states due to the spin-orbit split-off valence band as well as C-phonon replicas of intrinsic boron transitions associated with the states of the top of the valence band. More importantly, electrically neutral oxygen- related defects including interstitial oxygen also appear in the photoconductivity spectra as dips at the frequencies of the corresponding local vibrational modes. These findings demonstrate selectivity and high sensitivity of photoconductive spectroscopy, which make it a preferential technique to probe semiconductor thin films. [ABSTRACT FROM AUTHOR]

The hydrogen molecule H2 (or "hidden" hydrogen) in ZnO is studied by Raman scattering spectroscopy. It is shown that H2 is practically a free rotator stable up to 700 °C, which is formed by two mobile interstitial hydrogen atoms. The concentration profile of the hydrogen molecule anticorrelates with hydrogen substituting for oxygen (Ho) created at the sample surface during the high temperature hydrogenation. The H2 dissociation at elevated temperatures in the bulk regenerates interstitial (HBC) hydrogen, whereas the formation of Ho and hydrogen out-diffusion are dominant decay channels of the molecule near the surface. The latter mechanisms are responsible for the lower stability of H2 in the subsurface region. An ortho-para conversion between the nuclear spin states 1 and 0 of the molecule at 79 K was found to occur within 7.5 h, whereas the back conversion at room temperature occurs faster than 0.5 h. A shift in frequency of the H2 local vibrational mode with annealing time and temperature is associated with the thermal anneal of lattice imperfections. The coupling of transitions between rotational states of the molecule and lattice phonons influences the ro-vibrational properties. Interstitial lattice sites and/or larger vacancy clusters are preferred trapping centers for H2 in ZnO. [ABSTRACT FROM AUTHOR]

A Raman study on hydrogen donors in ZnO reveals the properties of bond-centered hydrogen (HBC) and hydrogen trapped in the oxygen vacancy (HO). The donors are identified by their electronic 1s→2s(2p) transitions and their characteristic local vibrational modes. The HO donor was detected preferentially below the sample surface, where a high oxygen vacancy concentration is generated by thermal treatment of the samples. HBC and HO exhibit different thermal stabilities and their concentrations depend strongly on the sample history. Molecular hydrogen is an essential part of the interplay of the two hydrogen donors. [ABSTRACT FROM AUTHOR]

Ion implantation is a widely used technique in the fabrication of semiconductor devices. We present a Raman scattering study of single crystalline silicon implanted with 28Si ions and subsequently treated in a hydrogen plasma. This treatment generates hydrogen molecules with a Raman signal at 3830 cm-1. The same band is detected in hydrogen implanted silicon employed in the ion-cut technology. The band reveals a substructure, which is assigned to the ro-vibrational transitions of H2 trapped at three different sites of the silicon lattice. The H2 signals are shown to correlate with the Si-H vibrational modes at 1888, 1930 and 1964 cm-1 which indicates the interstitial-type nature of the traps for the molecules. The properties of the traps are discussed. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Single crystalline silicon implanted with 28Si ions and subsequently hydrogenated from an rf plasma at 200 °C is studied by Raman and photoluminescence spectroscopy. A broad Raman band at 3830 cm-1 previously assigned to the rovibrational transitions of hydrogen molecules trapped in Si multivacancies [Ishioka et al, Phys. Rev. B 60, 10852 (1999)] reveals a complex line shape at 60 K. In contrast, our study correlates the Raman band to three different localized traps for hydrogen molecules which are identified from the dependence on the ion dose and annealing behavior. Each of these traps, which is saturated with H2, gives rise to three Raman transitions due to para- and ortho-2. The H2 signals are shown to correlate with the Si-H vibrational modes at 1888, 1930, and 1964 cm-1. Ortho to para conversion rates of H2 at 77 K and room temperature were found to be 62 ± 15 and 8 ± 2 h, respectively. [ABSTRACT FROM AUTHOR]

In this Letter we apply an innovative experimental approach, which allows us to improve the sensitivity of detecting local vibrational modes (LVMs) even in highly absorbing spectral regions. This photo-conductive technique allowed us to confirm a recent suggestion of a new multicenter bond for hydrogen in ZnO [A. Janotti and C.G. Van de Walle, Nature Mater. 6, 44 (2007)]. The two LVMs of the hydrogen substituting oxygen in ZnO are identified at 742 and 792 cm-1. The modes belong to a nondegenerated A ¡ and a twofold degenerated E representations of the C3u point group. The tetrahedral coordination of the hydrogen atom is the result of a newly detected multicenter bond for defects in solids. [ABSTRACT FROM AUTHOR]

An IR absorption study of single-crystal CdTe annealed in CdSO4 vapor at 850 °C is presented. It is shown that such a treatment results in the appearance of two absorption lines v1 and v2 at 1096.8 and 1108.4 cm-1, respectively [G. Chen et al., Phys. Rev. Lett. 96, 035508 (2006); Phys. Rev. B 75, 125204 (2007)]. Each of these features is accompanied by weaker lines. The intensities of each set of lines match the natural abundance of the sulfur isotopes. The v1 and v2 modes are assigned to the stretch vibrations of a sulfur-oxygen complex, Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed.. The number of oxygen atoms involved in Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. was deduced from the relative intensity of an IR absorption line related to the 18O isotope. [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]

Rovibrational Q(J) transitions of the interstitial H2 molecule in Si have been investigated by Raman scattering in the temperature range 90-388 K. In accordance with an earlier suggestion [ M. Hiller, E. V. Lavrov and J. Weber Phys. Rev. B 74 235214 (2006)], it is shown that the Q(2) transition of para hydrogen couples to the TAx phonon of Si and appears in the Raman spectra at temperatures above 200 K. The results presented also indicate that the rotational J=3 state of ortho hydrogen is resonantly coupled to the OΓ phonon. [ABSTRACT FROM AUTHOR]

The Zn vacancy passivated by two hydrogen atoms in ZnO (VZnH2) was studied by IR absorption. In addition to the ground state of the defect comprising two inequivalent O—H bonds aligned parallel and perpendicular to the c axis of the crystal, there exists a metastable state of the defect (VZnH2*). VZnH2* consists of two equivalent O—H bonds oriented perpendicular to the c axis. The metastable state reveals two local vibration modes at 3329.0 and 3348.4 cm-1, which represent antisymmetric and symmetric combinations of the two separate O—H stretch modes, respectively. The energy difference between the ground and the metastable states of the complex was found to be 75±9 meV. An activation energy of 0.96±0.12 eV is needed to move the hydrogen atom from the c axis to the perpendicular position. [ABSTRACT FROM AUTHOR]

A survey of recent Raman scattering studies on the interstitial hydrogen molecule (H2) in Si and GaAs is presented. It is shown that properties of H2 strongly depend on the nuclear spin state I. In either material, para-H2 (I=0) is unstable against irradiation with band gap light. In the case of Si, para-H2 also preferentially disappears from the Raman spectra in the course of storage at room temperature in the dark. Possible explanations for this surprising behavior are discussed and compared with the latest infrared absorption studies. [ABSTRACT FROM AUTHOR]

Two previously reported local vibrational modes (LVMs) in CdSe single crystals at 1992 and 2001 cm-1 [Chen et al., Phys. Rev. Lett. 101, 195502 (2008)] are generated in the present study by annealing the crystals in H2 gas at 500 °C. The absorption bands shift to 1454 and 1461 cmwhen the samples were annealed in ambient D2. Each LVM consists of at least five lines. The relative intensities match the natural abundance of the predominant Se isotopes. The 1992- and 2001-cm"' lines are assigned to two selenium-hydrogen vibrations in the Cd vacancy. [ABSTRACT FROM AUTHOR]

The preparation and characterization of Schottky contacts on differently grown n-type ZnO crystals was studied. We demonstrate that depending on the crystal growth process different procedures of surface treatment should be used to achieve good Schottky contacts. A treatment in a dc-hydrogen plasma enables us to fabricate Schottky contacts on hydrothermally grown ZnO, whereas a similar treatment of the vapor phase and melt grown ZnO resulted in the reduction in the diode rectification ratio. In the later samples a treatment in H2O2 significantly improves the quality of Schottky contacts. The origin of the different behavior will be discussed. [ABSTRACT FROM AUTHOR]

Li et al. [J. Appl. Phys. 105, 093516 (2009)] recently reported IR absorption study of hydrothermally grown ZnO. The authors investigated an IR absorption line at 2782.9 cm-1 and assigned it to a local vibrational mode of an OH–Ni complex. This comment provides experimental evidences that the assignment of Li et al. does not follow from the experimental data presented by the authors. [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]

A hydrogen-related defect in ZnO which causes two broad IR absorption bands at 3303 and 3321 cm-1 is studied by means of infrared absorption spectroscopy and first-principles theory. In deuterated samples, the defect reveals two sharp absorption lines at 2466 and 2488 cm-1 accompanied by weaker sidebands at 2462 and 2480 cm-1. Isotope substitution experiments with varying concentrations of H and D together with polarization-sensitive measurements strongly suggest that these IR absorption lines are due to stretch local vibrational modes of a defect comprising three equivalent hydrogen atoms. The zinc vacancy decorated by three hydrogen atoms, VZnH3, and ammonia trapped at the zinc vacancy, (NH3)Zn, are discussed as a possible origin for the complex. [ABSTRACT FROM AUTHOR]