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Zinc-doped monoclinic gallium oxide (β-Ga2O3:Zn) has semi-insulating properties that could make it a preferred material as a substrate for power devices. Infrared and UV/Visible spectroscopy were used to investigate the defect properties of bulk β-Ga2O3:Zn crystals. As-grown crystals contain a single O-H stretching mode at 3486.7 cm−1 due to a neutral ZnH complex. A deuterium-annealed sample displays the corresponding O-D stretching mode at 2582.9 cm−1, confirming the O-H assignment. A strong Ir4+ electronic transition at 5147.6 cm−1 is also observed, along with sidebands attributed to ZnIr pairs. These sidebands show distinct differences compared with Mg-doped samples; most importantly, several peaks are attributed to Ir4+ paired with a Zn on the tetrahedral Ga(I) site. Annealing under an oxygen atmosphere produced an insulating material with a resistance above 1 TΩ.

The band gap of uniaxially strained semi-insulating GaN:Mg has been examined using time-resolved optical transmission measurements in shock-wave experiments. For longitudinal stresses between 2.9 and 4.6 GPa, the absorption edge broadened significantly. Such a broadening is consistent with the presence of large piezoelectric fields (Franz–Keldysh effect) generated due to shock compression. For stresses greater than 4.6 GPa, however, the absorption edge remained relatively sharp. The sharp absorption onset suggests the presence of free charge carriers that screen the piezoelectric field, thereby suppressing the Franz–Keldysh effect. These observations indicate that electrical breakdown occurs at a field of 1 MV/cm. One possible mechanism that could result in free carriers is the dissociation of Mg–H complexes under the very high piezoelectric fields.

Zinc oxide (ZnO) is a wide-band gap semiconductor that has attracted tremendous interest for optical, electronic, and mechanical applications. First-principles calculations by [C. G. Van de Walle, Phys. Rev. Lett. 85, 1012 (2000)] have predicted that hydrogen impurities in ZnO are shallow donors. In order to determine the microscopic structure of hydrogen donors, we have used IR spectroscopy to measure local vibrational modes in ZnO annealed in hydrogen gas. An oxygen–hydrogen stretch mode is observed at 3326.3 cm−1 at a temperature of 8 K, in good agreement with the theoretical predictions for hydrogen in an antibonding configuration. The results of this study suggest that hydrogen annealing may be a practical method for controlled n-type doping of ZnO.

Phase separation was found to occur in In0.33Ga0.67N/GaN multiple-quantum-well structures after annealing at 975 °C in a hydrostatic pressure of 5 kbar N2 for 4 h. X-ray diffraction (XRD) spectra of the as-grown samples showed superlattice peaks that were replaced by a broad, single-phase peak after annealing. Transmission electron microscopy (TEM) images of the annealed samples show In-rich precipitates and voids that are found only within the quantum-well region. Both TEM and XRD measurements indicated that the formation of voids and second phases were suppressed after annealing in a hydrostatic pressure of 15 kbar. In addition, optical absorption measurements on these samples showed no indication of a peak at 2.65 eV that was observed in previous annealing studies.

Thick (225 nm) InxGa1−xN layers, grown on 5 μm thick GaN, were found by x-ray diffraction (XRD) measurements to be pseudomorphic up to x=0.114. Transmission electron microscopy showed that no misfit or additional threading dislocations were created at the InxGa1−xN/GaN interface. Composition of the overlayers was determined by Rutherford backscattering spectrometry and correlated to both the a and c lattice constants from XRD. It was found that Vegard’s law is applicable at these compositions, if the biaxial strain is included. Biaxial strain must also be considered to accurately determine the bowing parameter as shown by optical transmission measurements.

We report the results of a comparison study of photoluminescence (PL) from an In0.15Ga0.85N/GaN multiple-quantum-well (MQW) sample and an In0.11Ga0.89N thick epitaxial-layer sample, which have very similar band-gap energies. Large hydrostatic pressures were used for our investigations. The PL emissions in both samples were found to shift linearly to higher energy with applied pressure. In the MQW sample, the pressure response of the InGaN is dominated by the GaN layers, which leads to a significantly weaker pressure dependence as compared to the epilayer sample. Our results yield a pressure coefficient of 2.8×10−3 eV/kbar for the In0.15Ga0.85N/GaN MQW sample and 4.0×10−3 eV/kbar for the In0.11Ga0.89N epilayer. An abrupt decrease of PL intensity in both samples was observed at pressures above 100 kbar, indicating the carriers involved in the radiative recombination processes in the samples originate primarily from the adjacent GaN layers.

Interdiffusion of In and Ga is observed in InGaN/GaN multiple quantum wells for annealing temperatures of 1300–1400 °C. Hydrostatic pressures of up to 15 kbar were applied to prevent surface decomposition. In as-grown material, x-ray diffraction spectra show InGaN diffraction peaks up to the fourth order. After annealing at 1400 °C for 15 min, only the zero-order peak is observed, as a result of compositional disordering of the quantum well superlattice. Transmission electron microscopy confirms that the superlattice is completely disordered after annealing at 1400 °C for 15 min.

Evidence is presented for phase separation in In0.27Ga0.73N/GaN multiple quantum wells. After annealing for 40 h at a temperature of 950 °C, the absorption threshold at 2.95 eV is replaced by a broad peak at 2.65 eV. This peak is attributed to the formation of In-rich InGaN phases in the active region. X-ray diffraction measurements show a shift in the diffraction peaks toward GaN, consistent with the formation of an In-poor phase. A diffraction peak corresponding to an In-rich phase is also present in the annealed material. Nanoscale In-rich InGaN precipitates are observed by transmission electron microscopy and energy dispersive x-ray chemical analysis.

Local vibrational modes (LVMs) are reported for Mg‐doped GaN grown by metalorganic chemical vapor deposition. Hetero‐epitaxial layers of GaN:Mg, either as‐grown, thermally activated, or deuterated, were investigated with low‐temperature, Fourier‐transform infrared absorption spectroscopy. The as‐grown material, which was semi‐insulating, exhibits a LVM at 3125 cm−1. Thermal annealing increases the p‐type conductivity, as established with Hall effect measurements, and proportionally reduces the intensity of this LVM. Deuteration of the activated material creates a LVM at 2321 cm−1. The isotopic shift establishes the presence of hydrogen in the vibrating complex. The new LVMs are assigned to the stretch modes of the Mg–H and Mg–D complexes in GaN, with the vibrational frequencies indicative of a strong N–H bond as recently proposed from total‐energy calculations.

Using infrared absorption spectroscopy, we have observed hydrogen local vibrational modes (LVMs) in arsenic‐doped ZnSe grown by metalorganic chemical vapor deposition (MOCVD). When hydrogen is used as a carrier gas, we find an absorption peak at 2165.6 cm−1, which we attribute to a bond‐stretching mode of a hydrogen attached to an arsenic acceptor in a bond‐centered orientation. With deuterium substituting the hydrogen carrier gas, we find an additional peak at 1557.1 cm−1 with 1/3 the intensity of the hydrogen peak. The isotopic frequency ratio is r=vH/vD=1.3908, similar to values found in many hydrogen/deuterium‐related complexes. The larger area of the hydrogen peak indicates that most of the hydrogen comes from decomposition reactions involving the metalorganic molecules. The temperature dependent shift of the ZnSe:As,H mode is proportional to the lattice thermal energy U(T), a consequence of the anharmonic coupling between the LVMs and the lattice phonons.

A series of boron‐doped polycrystalline diamond films grown by direct current and microwave plasma deposition was studied with Raman and infrared (IR) absorption spectroscopy. A Fano line shape is observed in the Raman spectra for films with a boron concentration in a narrow range near 1021 cm−3. The appearance of the Fano line shape is correlated with the disappearance of discrete electronic transitions of the boron acceptor observed in the IR spectrum and the shift of the broadened peak to lower energy. The Fano interaction is attributed to a quantum mechanical interference between the Raman phonon (0.165 eV) and transitions from the broadened impurity band to continuum states composed of excited acceptor and valence band states.

Epitaxial β‐SiC films have been produced on Si(100) substrates by chemical vapor deposition (CVD) with 90% of the carbon supplied by methane and 10% by propane as compared to 100% by propane (or 100% by any carbon source more reactive than methane). These films, grown at 1350 °C in a CVD reactor, are single crystalline with a three‐dimensional surface morphology and have similar growth rates but lower carrier concentrations than films grown from propane and silane. The interplay of the chemistry of methane and evaporative loss of the Si substrate at ∼1100–1300 °C provide a reasonable explanation of our observations.

The incorporation and chemical bonding of fluorine introduced in SiO2 thin films by NF3‐enhanced oxidation of silicon has been studied by means of x‐ray photoelectron spectroscopy and secondary ion mass spectrometry depth profiling. Fluorine bonding in the oxide network is observed, indicated to occur in the area of the oxidizing interface and resulting in depth profiles which reflect the manner of the exposure of the growing oxide to the NF3 fluorine source during oxidation.

We combine the characterization techniques of scanning AC nanocalorimetry and x-ray diffraction to study phase transformations in complex materials system. Micromachined nanocalorimeters have excellent performance for high-temperature and high-scanning-rate calorimetry measurements. Time-resolved X-ray diffraction measurements during in-situ operation of these devices using synchrotron radiation provide unprecedented characterization of thermal and structural material properties. We apply this technique to a Fe_(0.84)Ni_(0.16) thin-film sample that exhibits a martensitic transformation with over 350 K hysteresis, using an average heating rate of 85 K/s and cooling rate of 275 K/s. The apparatus includes an array of nanocalorimeters in an architecture designed for combinatorial studies.

In2Se3 has potential as a phase-change material for memory applications. Understanding its phase diagram is important to achieve controlled switching between phases. Using x-ray diffraction and a diamond-anvil cell, the pressure-dependent structural properties of In2Se3 powder were studied at room temperature. α-In2Se3 transforms into the β phase at 0.7 GPa, an order of magnitude lower than phase-transition critical pressures in typical semiconductors. The β phase persists upon decompression to ambient pressure. Raman spectroscopy experiments confirm this result. The bulk moduli are reported and the c/a ratio for the β phase is shown to have a highly nonlinear dependence on pressure.

Zinc oxide single crystals were doped with copper acceptors by means of the nuclear transmutation doping method, which gives highly uniform dopant distributions and has a much higher probability of controlling the dopant locations in the lattice. The Cu doping was confirmed by the infrared absorption signature of Cu2+ at 5780 cm−1. Hall-effect measurements were performed to study the effect of CuZn on the electrical properties of ZnO. These measurements indicated that the Cu acceptor level lies 0.160 eV below the conduction-band minimum.

Dynamics of excess carriers, following a short excitation pulse, were recorded in shock-compressed [100] GaAs:Te to 4 GPa using time- and spectral-resolved photoluminescence (PL) measurements. PL signals extending over five orders of magnitude and comprising several recombination mechanisms were detected in single-event experiments. In marked contrast to earlier hydrostatic pressure results, a linear lifetime reduction was observed under uniaxial strain. The present results suggest that the lifetime reaches a minimum at the direct-to-indirect transition.

Real time changes of the GaAs band structure were determined using time-resolved photoluminescence (PL) spectroscopy, with nanosecond resolution, in single-event continuous compression experiments. Continuous compression to 5 GPa over 150 ns was achieved by impacting fused silica buffers preceding the GaAs crystals. PL spectra and compression wave profiles were measured simultaneously for uniaxial strain compression along the [100] orientation. Below 3 GPa, PL peaks from Te donors and Zn acceptors showed a blueshift upon compression, consistent with a widening of the band gap. At 3 GPa, the PL intensity decreased abruptly, due to a direct-to-indirect transition.

Cu doped ZnO and MgZnO ceramics were created via a process of cold pressing and annealing, and their optical properties and phonon dynamics were studied. It was found that the ceramics exhibit infrared absorption peak energies at 5783 and 5822 cm−1, indicative of intraband transitions in a substitutional Cu ion of oxidation state +2. The UV photoluminescence (PL) intensity of the ceramics was found to weaken significantly relative to an undoped sample. The low PL intensity is discussed in terms of the CuxZn1−xO alloy system and the indirect bandgap of the CuO end member, as well as in terms of the nonradiative Cu centers. Due to the weak PL, up to ten LO multiphonons were observed in the Raman spectra, pointing to a strong polaron coupling. The resonance behavior of the highest intensity mode was found to exhibit outgoing resonance characteristics.

Magnesium hydroxide [Mg(OH)2] thin layers were formed by a chemical reaction between Mg nanoblades and water. Infrared (IR) spectroscopy showed a OH bond-stretching vibrational mode at 3699cm−1. The assignment was verified by reactions with heavy water, producing OD bonds with the expected isotopic frequency shift. An asymmetric Fano line shape was observed for the OH layer on metallic Mg, while a symmetric Lorentzian (or Bright–Wigner) profile was observed for the OH layer on insulating MgH2. The results indicate that the OH layer on the Mg nanoblades is so thin that the vibrational mode couples to the free-electron continuum of Mg metal.

Changes in the indirect band gap of GaP due to uniaxial strain compression were observed using photoluminescence (PL) spectroscopy in shock wave experiments. Longitudinal stresses up to 5GPa were generated in [111], [110], and [100] orientated samples. PL lines from sulfur bound excitons exhibited redshifts upon shock compression. At larger uniaxial strains, the measured shifts were smaller than predicted from published optical deformation potentials for GaP. It is shown that overestimation of spin-dependent interactions is most likely responsible for the observed discrepancies. An accurate set of deformation potentials for GaP is derived.

The pressure response of the ultraviolet photoluminescence of ZnO nanocrystallites and MgZnO nanoalloy of composition 15% Mg:85% Zn of the wurtzite structure was studied. The authors found that up to 7GPa the pressure coefficients of ZnO and MgZnO are 23.6 and 27.1meV∕GPa, respectively. The pressure coefficient of the ZnO nanocrystallites is similar to that reported elsewhere for bulk ZnO material. The higher value found for MgZnO is discussed in terms of the d orbitals of the alloy constituents and their compliance to stress. Additionally, the volume deformation potential was derived from the experimental results.

Impurities play a major role in determining the optical and electrical properties of semiconductor nanoparticles. In this work, the presence and source of CO2 impurities in ZnO nanoparticles were studied by IR absorption spectroscopy. Isotopic substitution was used to verify the vibrational frequency assignment. Isochronal annealing experiments were performed to study the formation and stability of the molecular impurities. Our results indicate that the molecules are much more stable than CO2 adsorbed on bulk ZnO surfaces. By comparing our observations with similar results from IR spectroscopy of CO2 trapped in carbon nanotubes [C. Matranga, L. Chen, M. Smith, E. Bittner, J. K. Johnson, and B. Bockrath, J. Phys. Chem. B 107, 12930 (2003)], we conclude that the molecules are trapped in the ZnO nanoparticles.

Using infrared spectroscopy, local vibrational modes in GaP:Zn exposed to a remote hydrogen or deuterium plasma were observed. The modes at 2379.0 and 1729.4 cm−1 are assigned to hydrogen—phosphorus and deuterium—phosphorus bond‐stretching modes of complexes adjacent to the zinc acceptors. The isotopic ratio r=νH/νD=1.3756 is very close to that of the zinc‐hydrogen complex in InP (r=1.3744), which suggests that they have the same structure.