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Optical and electrical properties of Hf- and Zn-doped β-Ga2O3 samples, which are n-type and insulating, respectively, were altered via high-energy electron irradiation at 2.5 or 0.5 MeV. The β-Ga2O3:Hf samples irradiated with 2.5 MeV electrons experienced a color change from blue to yellow and a large drop in conductivity, attributed to the creation of gallium vacancies, which compensate donors. This irradiation resulted in the absence of free carrier absorption and the presence of Cr3+ photoluminescence (PL). PL mapping prior to irradiation revealed optically active ZnO precipitates that formed during the growth of β-Ga2O3:Zn. These precipitates have a 384 nm (3.23 eV) stacking fault emission in the core; in the outer shell of the precipitate, the PL blue-shifts to 377 nm (3.29 eV) and a broad defect band is observed. After 0.5 MeV electron irradiation, the defect band broadened and increased in intensity. The blue PL band (435 nm) of β-Ga2O3 was enhanced for both Hf- and Zn-doped samples irradiated with 0.5 MeV. This enhancement is correlated with an increase in oxygen vacancies. [ABSTRACT FROM AUTHOR]

When an impurity with a light mass is inserted into a crystal, it can undergo a high-frequency oscillation referred to as a local vibrational mode (LVM). A Fermi resonance may occur between the LVM and lower-frequency modes of the defect. The LVM may also interact with phonons or the electromagnetic field. Understanding these interactions can help model and control diffusion, defect reactions, and thermal conductivity. LVMs have been probed in semiconductors using pressure and alloying as experimental parameters, resulting in anticrossing between localized and extended vibrational modes. These types of vibrational interactions could play an important role in the stability and thermal properties of organic–inorganic hybrid semiconductors. The coupling between an LVM and electromagnetic wave yields an "LVM polariton," an excitation that has significant vibrational and electric-field amplitudes. [ABSTRACT FROM AUTHOR]

The effects of pressure on single crystals of Cr-doped gallium oxide (β-Ga2O3:Cr3+) and aluminum gallium oxide [(Al0.1Ga0.9)2O3] were examined by measuring the wavelength shift in the spectral R lines. Photoluminescence (PL) spectra of these materials were collected from samples in diamond anvil cells at pressures up to 9 GPa. The β-Ga2O3:Cr3+R lines were found to shift linearly under hydrostatic pressure. The (Al0.1Ga0.9)2O3R lines also show a linear shift but the R1 line shifted less than for β-Ga2O3:Cr3+. The ratio of R2 to R1 peak areas vs pressure is dominated by nonradiative recombination. X-ray diffraction measurements of (Al0.1Ga0.9)2O3 indicate that its equation of state is similar to that of β-Ga2O3. β-Ga2O3:Cr3+ was examined under non-hydrostatic conditions by using mineral oil as a pressure transmitting medium. Similar to the case in ruby, the R1 line is much more sensitive to non-hydrostatic stress than R2. Spatially resolved PL of a sample at 8 GPa in mineral oil showed significant variations in the R1 emission wavelength. These results suggest that the R1 line can serve as a sensitive probe of alloy composition and non-hydrostatic stress, while the R2 line is insensitive to these perturbations. [ABSTRACT FROM AUTHOR]

Transition-metal ions (Ni, Cu, and Zn) in β-Ga2O3 crystals form deep acceptor levels in the lower half of the bandgap. In the present study, we characterize the Ni acceptors in a Czochralski-grown crystal and find that their (0/−) level is approximately 1.40 eV above the maximum of the valence band. Both Ni2+ (3d8) and Ni3+ (3d7) acceptors are present in the as-grown crystal. Also present are unintentional Ir3+ (5d6) and Ir4+ (5d5) donors. The neutral Ni3+ acceptors have a low-spin S = 1/2 ground state and are easily monitored with electron paramagnetic resonance (EPR). Principal values of the g matrix for these acceptors are 2.131, 2.138, and 2.233. Although paramagnetic, the singly ionized Ni2+ acceptors are not seen with EPR at X band (9.4 GHz). The Ir4+ donors are monitored with EPR and with infrared absorption spectroscopy. Exposing the Ni-doped β-Ga2O3 crystal to 275 nm light at room temperature increases the concentration of Ni3+ ions and reduces the concentration of Ir4+ ions as electrons move from the acceptors to the donors. After illumination, heating the crystal above 375 °C restores the initial concentrations of the Ni3+ and Ir4+ ions. Broad optical absorption bands peaking near 303 and 442 nm are attributed to the Ni3+ acceptors. [ABSTRACT FROM AUTHOR]

Annealed bulk crystals of barium titanate (BaTiO3) exhibit persistent photoconductivity (PPC) at room temperature. Samples were annealed in a flowing gas of humid argon and hydrogen, with a higher flow rate corresponding to larger PPC. When exposed to sub-bandgap light, a broad infrared (IR) absorption peak appears at 5000 cm−1 (2 μm), attributed to polaronic or free-carrier absorption from electrons in the conduction band. Along with the increased IR absorption, electrical resistance is reduced by a factor of approximately two. The threshold photon energy for PPC is 2.9 eV, similar to the case of SrTiO3. This similarity suggests that the mechanisms are similar: an electron in substitutional hydrogen (HO) is photoexcited into the conduction band, causing the proton to leave the oxygen vacancy and attach to a host oxygen atom. The barrier to recover to the ground state is large such that PPC persists at room temperature. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) and optical absorption are used to characterize Cu2+ (3d9) and Cu3+ (3d8) ions in Cu-doped β-Ga2O3. These Cu ions are singly ionized acceptors and neutral acceptors, respectively (in semiconductor notation, they are Cu− and Cu0 acceptors). Two distinct Cu2+ EPR spectra are observed in the as-grown crystals. We refer to them as Cu2+(A) and Cu2+(B). Spin-Hamiltonian parameters (a g matrix and a 63,65Cu hyperfine matrix) are obtained from the angular dependence of each spectrum. Additional electron-nuclear double resonance (ENDOR) experiments on Cu2+(A) ions give refined 63Cu and 65Cu hyperfine matrices and provide information about the nuclear electric quadrupole interactions. Our EPR results show that the Cu2+(A) ions occupy octahedral Ga sites with no nearby defect. The Cu2+(B) ions, also at octahedral Ga sites, have an adjacent defect, possibly an OH− ion, an oxygen vacancy, or an H− ion trapped within an oxygen vacancy. Exposing the crystals at room temperature to 275 nm light produces Cu3+ ions and reduces the number of Cu2+(A) and Cu2+(B) ions. The Cu3+ ions have an S = 1 EPR spectrum and are responsible for broad optical absorption bands peaking near 365, 422, 486, 599, and 696 nm. An analysis of loops observed in the Cu3+ EPR angular dependence gives 2.086 for the g value and 22.18, 3.31, and −25.49 GHz for the principal values of D (the fine-structure matrix). Thermal anneal studies above room temperature show that the Cu3+ ions decay and the Cu2+ ions recover between 75 and 375 °C. [ABSTRACT FROM AUTHOR]

In this study, the formation and character of gallium vacancies (VGa) and their complexes in near surface and bulk regions of single crystal β-Ga2O3 were explored using unintentionally doped single crystals grown by the Czochralski method. As-grown and O2 annealed (up to 1550 °C) samples were investigated using positron annihilation spectroscopy (PAS) to study the top 0.05–6 μm, and also current–voltage measurements and infrared (IR) spectroscopy, with hydrogenated samples to probe VGa, to study the bulk. After annealing in O2 > 1000 °C, the β-Ga2O3 resistivity begins increasing, up to ∼109 Ω cm for 1550 °C treatment, with the top 0.5 mm being many orders of magnitude more resistive. PAS measurements of the top 6 μm (S values) and very near surface 200 nm (diffusion length, L) indicate differential behavior as a function of peak annealing temperature. At least four temperature regimes of behavior are described. VGa are present in the bulk after growth, but considerable changes occur upon annealing at a temperature ≈1000 °C, where L and S decrease simultaneously, suggesting an increasing defect concentration (L) but a decreasing defect volume (S). Annealing at a temperature ≈1400 °C increases S again, showing an increasing volume concentration of VGa, with IR absorption showing a large signature of VGa-2H, indicative of increased VGa formation that was not present when annealing at a temperature ≈1000 °C. These results suggest that defect changes from annealing in oxygen are depth dependent, and that VGa configuration may not be the same near the oxygen-exposed surface of the sample and in the bulk. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) is used to identify and characterize neutral zinc acceptors in Zn-doped β-Ga2O3 crystals. Two EPR spectra are observed at low temperatures, one from Zn ions at tetrahedral Ga(1) sites (the Z n Ga 1 0 acceptor) and one from Zn ions at octahedral Ga(2) sites (the Z n Ga 2 0 acceptor). These Zn acceptors are small polarons, with the unpaired spin localized in each case on a threefold coordinated oxygen O(I) ion adjacent to the Zn ion. Resolved hyperfine interactions with neighboring 69Ga and 71Ga nuclei allow the EPR spectra from the two acceptors to be easily distinguished: Z n Ga 1 0 acceptors interact equally with two Ga(2) ions and Z n Ga 2 0 acceptors interact unequally with a Ga(1) ion and a Ga(2) ion. The as-grown crystals are compensated, with the Zn ions initially present as singly ionized acceptors (Z n Ga 1 − and Z n Ga 2 −). Exposing a crystal to 325 nm laser light, while being held at 140 K, primarily produces neutral Z n Ga 2 0 acceptors when photoinduced holes are trapped at Z n Ga 2 − acceptors. This suggests that there may be significantly more Zn ions at Ga(2) sites than at Ga(1) sites. Warming the crystal briefly to room temperature, after removing the light, destroys the EPR spectrum from the shallower Z n Ga 2 0 acceptors and produces the EPR spectrum from the more stable Z n Ga 1 0 acceptors. The Z n Ga 2 0 acceptors decay in the 240–260 K region with a thermal activation energy near 0.65 eV, similar to Mg Ga 2 0 acceptors, whereas the slightly deeper Z n Ga 1 0 acceptors decay close to room temperature with an approximate thermal activation energy of 0.78 eV. [ABSTRACT FROM AUTHOR]

In the field of high-power electronics, gallium oxide (Ga2O3) is attracting attention due to its wide bandgap and ability to be doped n-type. Point defects, including vacancies, impurities, and dopants, play important roles in optimizing device performance. This tutorial discusses the fundamental properties of point defects in monoclinic β-Ga2O3 and the methods employed to study them. Oxygen vacancies are deep donors that do not cause n-type conductivity but may compensate acceptors. Gallium vacancies are deep acceptors that can be partially passivated by hydrogen. Substitutional magnesium is a promising acceptor that produces a semi-insulating material and also forms a complex with hydrogen. Calcium and iron also have deep acceptor levels. Iridium deep donors are introduced into crystals grown from a melt in an Ir crucible. Other defects are introduced by irradiation with energetic particles such as neutrons or protons. In addition to altering the electronic properties, defects give rise to UV/visible emission bands in photoluminescence and cathodoluminescence spectra. [ABSTRACT FROM AUTHOR]

Gallium oxide is a promising semiconductor for its potential as a material in the field of power electronics. The effects of iridium impurities on undoped, Mg-doped, and Ca-doped gallium oxides were investigated with IR spectroscopy. In undoped and Ca-doped β-Ga2O3, IR peaks at 3313, 3450, and 3500 cm−1 are tentatively assigned to O–H bond-stretching modes of IrH complexes. Mg-, Ca-, and Fe-doped samples show an Ir4+ electronic transition feature at 5148 cm−1. By measuring the strength of this feature vs photoexcitation, the Ir3+/4+ donor level was determined to lie 2.2–2.3 eV below the conduction band minimum. Ga2O3:Mg also has a range of sidebands between 5100 and 5200 cm−1, attributed to IrMg pairs. Polarized IR measurements show that the 5248 cm−1 peak is anisotropic, weakest for light polarized along the c axis, consistent with Lenyk et al. [J. Appl. Phys. 125, 045703 (2019)]. [ABSTRACT FROM AUTHOR]

ZnS1-xOx is a highly mismatched semiconductor alloy with potential light-emitting and solar-cell applications. In this work, optical transmission spectroscopy and a modified derivative method were employed to determine the room-temperature bandgap of cubic (zinc blende) ZnS1-xOx from x = 0.01 to 0.3. The bandgap drops steeply for dilute oxygen concentrations, followed by a more gradual decrease for x > 0.05. This nonlinear behavior is attributed to a transition from isolated oxygen impurities to pairs and larger clusters. Alloying with x = 0.3 causes bandgap to drop from 3.7 to 3.1 eV. Previous work showed that the bandgap of wurtzite ZnS1-xOx shifts from 3.7 to 2.8 eV over the same composition range. [ABSTRACT FROM AUTHOR]

All semiconductors, whether by design or by accident, contain defects. In addition to traditional semiconductors (elemental, III-V, and II-VI), emerging materials include organic semiconductors, nitrides, oxides, and topological insulators, in bulk crystal and thin-film forms as well as low-dimensional and nanoscale structures. SUMMARY OF AREAS COVERED A. Group-IV semiconductors Semiconductors composed of group-IV elements (C, Si, and Ge) continue to be an active area of investigation. The growth of GaN[26] and InGaN/GaN quantum-well structures[27] on silicon substrates results in extended defects such as V-pits and line defects. [Extracted from the article]

Annealed strontium titanate (SrTiO3 or STO) single crystals exhibit persistent photoconductivity (PPC) at room temperature. Illumination with sub-gap light reduces the resistance by three orders of magnitude, which persists for weeks or longer. The defects responsible for this remarkable phenomenon have not been identified. In this work, we report on the importance of hydrogen and oxygen during the annealing process that is used to induce PPC. The results from IR spectroscopy and two-point resistance measurements indicate that water vapor at 1200 °C yields hydrogen and oxygen-vacancy populations that result in large PPC. Deuterium substitution experiments show evidence for a two-hydrogen center that forms after exposure to light. The results suggest that light causes substitutional hydrogen to leave the oxygen site, forming metastable O-H bonds. This process liberates electrons and causes PPC. [ABSTRACT FROM AUTHOR]

ZnS1−xOx alloy films were studied via resonant Raman spectroscopy. Films with a low oxygen content exhibit ZnS longitudinal optical modes and additional modes attributed to O local vibrational modes (LVMs). The frequencies of these modes are explained by a simple mass-defect model. As the O content increases, pairs and larger clusters form, causing the O mode to transition from an LVM to a delocalized phonon. The composition dependence of the modes shows agreement with the modified random element isodisplacement model. Low-temperature measurements show that the O-related mode is composed of multiple features, attributed to zincblende and wurtzite structural regions. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) is a wide band gap semiconductor and a potential candidate for next generation white solid state lighting applications. In this work, hydrogen-related complexes in lithium diffused ZnO single crystals were studied. In addition to the well-known Li-OH complex, several other hydrogen defects were observed. When a mixture of Li2O and ZnO is used as the dopant source, zinc vacancies are suppressed and the bulk Li concentration is very high (>1019cm-3). In that case, the predominant hydrogen complex has a vibrational frequency of 3677 cm-1, attributed to surface O-H species. When Li2CO3 is used, a structured blue luminescence band and O-H mode at 3327 cm-1 are observed at 10K. These observations, along with positron annihilation measurements, suggest a zinc vacancy–hydrogen complex, with an acceptor level ∼0.3 eV above the valence-band maximum. This relatively shallow acceptor could be beneficial for p-type ZnO. [ABSTRACT FROM AUTHOR]

Point defects affect or even completely determine physical and chemical properties of semiconductors. Characterization of point defects based on experimental techniques alone is often inconclusive. In such cases, the combination of experiment and theory is crucial to gain understanding of the system studied. In this tutorial, we explain how and when such comparison provides new understanding of the defect physics. More specifically, we focus on processes that can be analyzed or understood in terms of configuration coordinate diagrams of defects in their different charge states. These processes include light absorption, luminescence, and nonradiative capture of charge carriers. Recent theoretical developments to describe these processes are reviewed. [ABSTRACT FROM AUTHOR]

The MgxZn1-xO alloy system is emerging as an environmentally friendly choice in ultraviolet lighting and sensor technologies. Knowledge of defects which impact their optical and material properties is a key issue for utilization of these alloys in various technologies. The impact of phase segregation, structural imperfections, and alloy inhomogeneities on the phonon dynamics and electronic states of MgxZn1-xO thin films were studied via selective resonant Raman scattering (SRRS) and Urbach analyses, respectively. A series of samples with Mg composition from 0-68% were grown using a sputtering technique, and the optical gaps were found to span a wide UV range of 3.2-5.8 eV. The extent of the inherent phase segregation was determined via SRRS using two UV-laser lines to achieve resonance with the differing optical gaps of the embedded cubic and wurtzite structural domains. The occurrence of Raman scattering from cubic structures is discussed in terms of relaxation of the selection rules due to symmetry breaking by atomic substitutions. The Raman linewidth and Urbach energy behavior indicate the phase segregation region occurs in the range of 47-66% Mg. Below the phase segregation, the longitudinal optical phonons are found to follow the model of one-mode behavior. The phonon decay model of Balkanski et al. indicates that the major contributor to Raman linewidth arises from the temperature-independent term attributed to structural defects and alloy inhomogeneity, while the contribution from anharmonic decay is relatively small. Moreover, a good correlation between Urbach energy and Raman linewidth was found, implying that the underlying crystal dynamics affecting the phonons also affect the electronic states. Furthermore, for alloys with low Mg composition structural defects are dominant in determining the alloy properties, while at higher compositions alloy inhomogeneity cannot be neglected. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) has potential for a range of applications in the area of optoelectronics. The quest for p-type ZnO has focused much attention on acceptors. In this paper, Cu, N, and Li acceptor impurities are discussed. Experimental evidence indicates these point defects have acceptor levels 3.2, 1.4, and 0.8 eV above the valence-band maximum, respectively. The levels are deep because the ZnO valence band is quite low compared to conventional, non-oxide semiconductors. Using MoO2 contacts, the electrical resistivity of ZnO:Li was measured and showed behavior consistent with bulk hole conduction for temperatures above 400 K. A photoluminescence peak in ZnO nanocrystals is attributed to an acceptor, which may involve a Zn vacancy. High field (W-band) electron paramagnetic resonance measurements on the nanocrystals revealed an axial center with g⊥=2.0015 and g‖=2.0056, along with an isotropic center at g=2.0035. [ABSTRACT FROM AUTHOR]

Electron Paramagnetic Resonance was used to study N2-centers in ZnO, which show a 5-line spectrum described by the hyperfine interaction of two nitrogen nuclei (nuclear spin I=1, 99.6% abundance). The recharging of this center exhibits two steps, a weak onset at about 1.4 eV and a strongly increasing signal for photon energies above 1.9 eV. The latter energy coincides with the recharging energy of NO centers (substitutional nitrogen atoms on oxygen sites). The results indicate that the N2-centers are deep level defects and therefore not suitable to cause significant hole-conductivity at room temperature. [ABSTRACT FROM AUTHOR]

Micromachined nanocalorimetry sensors have shown excellent performance for high-temperature and high-scanning rate calorimetry measurements. Here, we combine scanning AC nanocalorimetry with in-situ x-ray diffraction (XRD) to facilitate interpretation of the calorimetry measurements. Time-resolved XRD during in-situ operation of nanocalorimetry sensors using intense, high-energy synchrotron radiation allows unprecedented characterization of thermal and structural material properties. We demonstrate this experiment with detailed characterization of the melting and solidification of elemental Bi, In, and Sn thin-film samples, using heating and cooling rates up to 300 K/s. Our experiments show that the solidification process is distinctly different for each of the three samples. The experiments are performed using a combinatorial device that contains an array of individually addressable nanocalorimetry sensors. Combined with XRD, this device creates a new platform for high-throughput mapping of the composition dependence of solid-state reactions and phase transformations. [ABSTRACT FROM AUTHOR]

MgZnO alloys are potentially important semiconductors for UV optoelectronics and other applications. Since device heterostructures are under significant strain, it is important to determine the elastic properties of these materials, in the bulk and nanoscale. In this work, the equations of state were obtained for ZnO and MgxZn1-xO alloys under hydrostatic pressure, using x-ray diffraction. The equations of state were found to be insensitive to Mg content up to x = 0.2. The pressure dependence of the c/a ratio also did not depend on Mg content, within experimental uncertainty. Combining these results with previous ultrasonic measurements, the following elastic constants were determined to be valid for wurtzite MgxZn1-xO (x≤ 0.2): C11 = 207 GPa, C12 = 118 GPa, C33 = 210 GPa, and C13 = 106 GPa. These elastic constants yield a bulk modulus of 143 GPa and c/a slope of -3×10-4GPa-1. Nanocrystals showed the same bulk moduli as their bulk counterparts. However, nanocrystals showed consistently steeper c/a slopes, suggesting subtle differences in their elastic constants. [ABSTRACT FROM AUTHOR]

Hydrogen has a significant impact on the structural and electronic properties of metals, insulators, and semiconductors. Despite the prevalence of hydrogen, little is known about its behavior in oxides such as strontium titanate (SrTiO3). In this work, hydrogen-related defects in SrTiO3 were investigated using infrared absorption spectroscopy. Two local vibrational modes (LVMs) are observed at 3355 and 3384 cm-1 after hydrogenation at 800 °C. Isotope substitution experiments revealed that the defect consists of two hydrogen atoms bound to host oxygen atoms. From the temperature dependence of the LVMs, we ascribe the complex to a strontium vacancy passivated by two hydrogen atoms. The thermal stability of the defect was determined through a series of isochronal annealing experiments on the hydrogenated SrTiO3 sample. These measurements provided evidence of 'hidden hydrogen,' possibly H2 molecules, in the crystal. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) is semiconductor with a wide band gap of 3.4 eV. It continues to gain more attention not only for its versatile use in industry but also its potential for further application in electronics, optics, spintronics, and transparent circuits. Many of these applications require p-type ZnO. Nitrogen substituting for oxygen is a possible acceptor for such applications. In this paper, we report a study of nitrogen-hydrogen (N–H) complexes grown into single-crystal ZnO, using seeded chemical vapor transport in an ammonia ambient. An infrared (IR) absorption peak arising from N–H complexes was observed at 3150.6 cm-1 at liquid-helium temperatures. The assignment of this peak was confirmed by nitrogen and hydrogen isotope substitution. Polarized IR spectroscopy shows that the N–H dipole is oriented at an angle ∼114° to the c axis, in agreement with previous first-principles calculations. To probe the stability of the N–H complexes, samples were annealed in air, oxygen, and argon. Samples annealed in oxygen at 725 °C showed a significant increase in resistivity, due to outdiffusion of hydrogen and compensation by nitrogen acceptors. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) is a wide band gap semiconductor with potential applications in optoelectronics, transparent electronics, and spintronics. The high efficiency of UV emission in this material could be harnessed in solid-state white lighting devices. The problem of defects, in particular, acceptor dopants, remains a key challenge. In this review, defects in ZnO are discussed, with an emphasis on the physical properties of point defects in bulk crystals. As grown, ZnO is usually n-type, a property that was historically ascribed to native defects. However, experiments and theory have shown that O vacancies are deep donors, while Zn interstitials are too mobile to be stable at room temperature. Group-III (B, Al, Ga, and In) and H impurities account for most of the n-type conductivity in ZnO samples. Interstitial H donors have been observed with IR spectroscopy, while substitutional H donors have been predicted from first-principles calculations but not observed directly. Despite numerous reports, reliable p-type conductivity has not been achieved. Ferromagnetism is complicated by the presence of secondary phases, grain boundaries, and native defects. The famous green luminescence has several possible origins, including Cu impurities and Zn vacancies. The properties of group-I (Cu, Li, and Na) and group-V (N, P, As, and Sb) acceptors, and their complexes with H, are discussed. In the future, doping of ZnO nanocrystals will rely on an understanding of these fundamental properties. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) spectra of bound excitons were measured in uniaxially strained GaP by performing shock-wave experiments at liquid nitrogen temperatures. GaP samples doped with sulfur or nitrogen were compressed up to 3 GPa when subjected to uniaxial strains along the [100] crystallographic orientation. PL lines from shallow sulfur donors redshifted upon compression, tracking the reduction in the indirect band gap. PL lines related to the isoelectronic NN1 pairs, in contrast, exhibited splitting and nonlinear blueshift. An empirical approach was used to model the NN1 behavior. It was shown that the splitting pattern is consistent with the previously proposed symmetry of NN1 defects and nonlinearities resulting from the reduction in the exciton binding energy. At high stresses, the NN1 lines disappeared due to the ionization of bound excitons. [ABSTRACT FROM AUTHOR]

MgxZn1-xO (x=0.15) and ZnO nanocrystals of about 40 nm in diameter were studied using x-ray diffraction and diamond-anvil cells. The equation of state (EOS) for MgZnO is reported for the first time. Between pressures of 9.45 and 10.7 GPa, MgZnO transforms into the rocksalt (NaCl) structure, which persisted to 1.1 GPa upon decompression. The EOS parameters for ZnO are close to their bulk values and in good agreement with values obtained previously. The bulk modulus for MgZnO was slightly lower than that of ZnO. The pressure-induced decrease in c/a ratio was greater for MgZnO, consistent with the tendency for MgZnO to move toward a cubic structure. From previous photoluminescence measurements [J. Huso et al., Appl. Phys. Lett. 89, 171909 (2006)], the band-gap volume deformation potentials for ZnO and Mg0.15Zn0.85O were determined to be -3.6 and -4.0 eV, respectively. [ABSTRACT FROM AUTHOR]

We studied the dopant concentration distribution and conductivity in ZnO:Mn films grown by metalorganic chemical vapor deposition. The ion beam, surface, and microstructural properties of undoped ZnO films were compared with Mn-doped ZnO films. Suppression of ZnO conductivity was observed for Mn doping up to ∼4.5 at. %. The presence of Mn2+, confirmed by x-ray photoelectron spectroscopy, is correlated with the reduction in conductivity. Variable-temperature Hall effect measurements yield an activation energy of 170 meV, consistent with deep donors in the bulk or at the interface. The results suggest that the incorporation of substitutional Mn suppresses the formation of native defects such as oxygen vacancies. [ABSTRACT FROM AUTHOR]

The effect of hydrogen on the conductivity of ZnO nanoparticles has implications for nanoscale optoelectronic devices. In this study, infrared reflectance spectra of as-grown and hydrogen-annealed ZnO nanoparticles were measured at near-normal incidence. The as-grown particles were electrically semi-insulating and show reflectance spectra characteristic of insulating ionic crystals. Samples annealed in hydrogen showed a significant increase in electrical conductivity and free-carrier absorption. A difference was observed in the reststrahlen line shape of the conductive sample compared to that of the as-grown sample. The effective medium approximation was applied to model the reflectance and absorption spectra. The agreement between experimental results and the model suggests that the nanoparticles have inhomogeneous carrier concentrations. Exposure to oxygen for several hours led to a significant decrease in carrier concentration, possibly due to the adsorption of negative oxygen molecules on the nanoparticle surfaces. [ABSTRACT FROM AUTHOR]

Presents information on a study which dealt with issues relating to local vibrational modes in semiconductors, with an emphasis on infrared and Raman spectroscopy. Theory; Experimental techniques; Discussion on the microscopic structure of oxygen in silicon.

The infrared and x-ray photoelectron spectroscopy techniques are employed to analyze the mechanisms involved in the inclusion of Cu acceptor dopants into the ZnO nanocrystals during its growth. An increase in the average diameter of the nanocrystals is shown to lead to a significant enhancement in the incorporation of the Cu dopants in the system.

X-ray diffraction and diamond-anvil cells are used for studying [Mg.sub.x][Zn.sub.1-x]O and ZnO nanocrystals of about 40 mm in diameter. The equation of state (EOS) parameters for ZnO is close to their bulk values and the bulk modulus for MgO is lower than that of ZnO.

Infrared reflectance spectra of as-grown and hydrogen-annealed ZnO nanoparticles are measured at near-normal incidence by using infrared and Raman spectroscopy. The results have shown that exposure to oxygen has led to a significant decrease in carrier concentration, which is due to the adsorption of negative oxygen molecules on the nanoparticles surfaces.