Energy Position Of Peak Research Articles

Experimental evidence for a Be shallow acceptor in GaN grown on Si(111) by molecular beam epitaxy

Be-doped GaN layers have been grown on Si(111) by molecular beam epitaxy. The relative Be concentration was measured by secondary ion mass spectroscopy analysis. Photoluminescence spectra have been taken under continuous wave and time-resolved conditions. A new emission at 3.384 eV, which is probably related to substitutional Be, is reported, together with its first and second order phonon replica. Clear blue-shifts are observed when increasing temperature and excitation power, suggesting that this emission is associated with a transition from a residual donor to the Be acceptor. From time-resolved spectra, a very slow and strongly non-exponential decay, as well as a red-shift of the peak energy position with time, confirm the donor-acceptor character of the Be-related emission. The estimated ionization energy of the acceptor is around 90 meV, so Be is the shallowest p-dopant ever reported in GaN.

Dependence of the photoluminescence of Tl 2InGaS 4 layered crystal on temperature and excitation intensity

The emission band spectra of Tl 2InGaS 4 layered crystals were investigated in the 10–120 K temperature range and in the 540–860 nm wavelength range using photoluminescence (PL). The peak energy position of the emission band is located at 1.754 eV (707 nm) at 10 K. The emission band has a half-width of 0.28 eV and an asymmetric Gaussian lineshape. The increase of the half-width of the emission band, the blue shift of the emission band peak energy and the quenching of the PL with increasing temperature is explained using the configuration coordinate model. The blue shift of the emission band peak energy and the sublinear increase of the emission band intensity with increasing excitation intensity is explained using the inhomogenously spaced donor–acceptor pair recombination model.

Using X-ray absorption to probe sulfur oxidation states in complex molecules

X-ray absorption near-edge structure (XANES) spectroscopy offers an important non-destructive tool for determining oxidation states and for characterizing chemical speciation. The technique was used to experimentally verify the oxidation states of sulfur in different types of complex molecules because there are irregularities and uncertainties in assigning the values traditionally. The usual practice of determining oxidation states involves using a set of conventional rules. The oxidation state is an important control in the chemical speciation of sulfur, ranging from −2 to +6 in its different compounds. Experimental oxidation-state values for various types of sulfur compounds, using their XANES peak-energy positions, were assigned from a scale in which elemental sulfur and sulfate are designated as 0 and +6, respectively. Because these XANES-based values differed considerably from conventionally determined oxidation states for most sulfur compounds, a new term ‘oxidation index’ was coined to describe them. The experimental values were closer to those conventional values obtained by assigning shared electrons to the more electronegative atoms than to those based on other customary rules for assigning them. Because the oxidation index is distinct and characteristic for each different type of sulfur functionality, it becomes an important parameter for characterizing sulfur species, and for experimentally verifying uncertain oxidation states.

Impurity Levels in p-Type Layered Semiconductor InSe Doped with Hg

Photoluminescence (PL) and Hall effect measurements have been made on Hg-doped p-type InSe. A broad emission band at 1.237 eV (77 K) is mainly observed on the PL spectra of samples doped with Hg and, in the range 0.02 to 0.1 at%, the PL intensity increases with increasing Hg concentration. From the temperature dependences of the PL intensity and peak energy position, we show that the 1.237 eV emission band is due to the transition between a shallow donor level and a deep acceptor level, at 0.07 eV above the valence band. The dominant acceptor level in the carrier transport measurements shows the same energy position as the radiative recombination center.

Impurity Levels in p-Type Layered Semiconductor InSe Doped with Hg

Photoluminescence (PL) and Hall effect measurements have been made on Hg-doped p-type InSe. A broad emission band at 1.237 eV (77 K) is mainly observed on the PL spectra of samples doped with Hg and, in the range 0.02 to 0.1 at%, the PL intensity increases with increasing Hg concentration. From the temperature dependences of the PL intensity and peak energy position, we show that the 1.237 eV emission band is due to the transition between a shallow donor level and a deep acceptor level, at 0.07 eV above the valence band. The dominant acceptor level in the carrier transport measurements shows the same energy position as the radiative recombination center.

Growth of cubic III-nitrides by gas source MBE using atomic nitrogen plasma: GaN, AlGaN and AlN

Cubic GaN, AlGaN and AlN epilayers were grown on 3C-SiC(001) substrates by gas source molecular beam epitaxy using radio-frequency N2 plasma containing atomic nitrogen species. Due to the enhancement of growth rate by this plasma source, cubic GaN epilayers with the thickness of several micrometers were obtained, and the quality of epilayers was so much improved that they showed an X-ray diffraction peak width as small as 9min. Cubic AlxGa1−xN and cubic AlN epilayers were also grown, and the variations of X-ray diffraction peak position and emission energy were observed according to the Al content.

X-Ray Photoelectron Spectroscopy Study of Oxygen and Argon Annealed YBa2Cu3O7-δ

X-ray Photoelectron Spectroscopy (XPS) measurements have been performed on oxygen- and argon-annealed YBa 2 Cu 3 O 7-δ (YBCO) and the results are compared with similar measurements performed on Y 2 O 3. The structural changes in oxygen- and argon-annealed YBCO are reflected in the shift of the Binding Energy (BE) peak positions for the various components existing in the YBCO lattice.

Saturation of Intersubband Absorption by Real-Space Transfer in Modulation Doped Single GaAs–AlAs Quantum Well

Intersubband absorption spectrum was investigated with intense infrared light in a modulation doped GaAs quantum well (QW) of 10 nm thickness with 6 nm AlAs barriers. When the excitation intensity was 9.8 kW/cm, the absorption was bleached to half of its weak field value. The corresponding effective intersubband relaxation time t was 14 ps, which is much larger than the intersubband LO phonon emission time. We also observed that the peak position energy Ep shifts toward lower photon energy as the excitation intensity is increased, however, the amount of the shift was about a factor four smaller than the value predicted from the depolarization effect. The observed large t and the small shift of Ep indicates an efficient real-space transfer of the excited electrons. The escape of electrons was directly detected as a photocurrent.

Electronic and optical properties of strained wurtzite GaN

Band structures of wurtzite GaN (α-GaN) under strains in the region -5%−5% are calculated in a tight-binding framework. The empirical scaling rule has been used for considering the effects of hydrostatic strains. The scaling indexes are determined by fitting the deformation-potential constants with other theoretical values. The band gap at Γ point increases with the absolute value of strains. GaN turns to be of indirect band gap when strains reach 5%. The density of states and the imaginary part of dielectric function (2 (ω)) are studied. Both the shape and energy position of the highest peak in the 2 (ω) spectrum successively change with the strains. The real part of dielectric function, refractive index and the effects of the strains on them are also shown.

Two-photon spectroscopy of Eu 2+ in cubic perovskite KMgF 3

Two-photon excitation of the intra-configurational f-f transitions of Eu 2+ in the cubic host KMgF 3 were studied. The fully resolved Stark structure of the 6P 7 2 , 5 2 excited multiplets support the picture of a cubic environment for the majority of the Europium ions, as well as the presence of sites of lower symmetry. Transitions to the 6D j multiplet were also measured for the first time in this host together with the temperature dependence of the line shape and peak energy position for all observed transitions.

Low temperature photoluminescence properties of InGaN films grown on (0 1 [formula omitted] 2) Al 2O 3 and (0 0 0 1) Al 2O 3 substrates by low pressure MOVPE

Low temperature photoluminescence (PL) properties of InGaN films grown on (0 1 1 2) Al 2O 3 and (0 0 0 1) Al 2O 3 substrates by low pressure MOVPE were studied at 11 K. In the PL spectrum of a In 0.11Ga 0.89N AlN buffer/(0 1 1 2)Al 2O 3 film, only one near band edge emission with wavelength 371.4 nm was observed in the range from 350 nm to 630 nm. For In x Ga 1− x N/GaN/GaN buffer/(0 0 0 1)Al 2O 3 films with x = 0.02 and 0.035, similar PL spectra of GaN films, the recombinations of an exciton bound to a neutral donor ( I 2 lines) were observed and seem to be dominant. The peak energy positions were 3.467 eV, 3.454 eV and 3.449 eV for x = 0, 0.02 and 0.03, respectively. It was found that FWHM roughly increase as x increases. Donor-Acceptor (D-A) pair combination near 3.27 eV and their LO-phonon replica (near 3.18 eV) also appeared in the PL spectra. The LO-phonon energy of In x Ga 1− x N shift to high energy compared to GaN. It is suggested that the D-A pair recombination contributes to the transitions from a shallow donor to a carbon-related acceptor level.

Total reflection of energetic ions from crystal surfaces at glancing incidence

A two-dimensional classical dynamics model for calculating the reflection coefficient of keV-ion beams backscattered from a crystal surface at glancing incidence is presented. The target is considered as consisting of one or two layers of atomic strings. A string potential of cylindrical symmetry was constructed by using the well-known iuniversali pair potential or the Molire interatomic potential. The critical transverse energy needed for a 100% reflection of light ions from the surface is assessed for the most open (11 _ 0) direction of Cu(111), Ni(111), and Al(111) crystal surfaces. The distribution of the backscattered ions on the azimuthal scattering angle exhibits the multimode structure related to the zig-zag trajectories in surface semichannels. The energy spectra are compared to the experimental data. The simulations show that the reflection coefficient is substantially dependent on the interatomic potential used but is not much affected by the model adopted for description of the inelastic losses. The inelastic-interaction model affects mostly the energy peak position, so that an estimate based on OennRobinson empirical formulae compares better with the experimental data than the original Firsov model. Resume : Nous prOsentons un modle de dynamique classique en 2-D pour calculer le

Intersubband transitions in strainedIn0.07Ga0.93As/Al0.40Ga0.60As multiple quantum wells and their application to a two-colors photodetector

Infrared absorption spectroscopy is used to study the conduction band intersubband transitions in Si-doped ${\mathrm{In}}_{0.07}$${\mathrm{Ga}}_{0.93}$As/${\mathrm{Al}}_{0.40}$${\mathrm{Ga}}_{0.60}$As multiple quantum-well structures with the doping being restricted to the well region. The chemical potential determined by the electron density is designed to be above the second subband edge for samples with certain well widths, so that two absorption peaks with a different wavelength would be observed as one of the requirements for a two-colors photodetector. The optical absorption spectra are calculated from which the peak position energies are extracted and compared with the experimental measurements for different well widths. Good agreement between numerical results and experimental data is achieved. In our theory, self-consistent screened Hartree-Fock calculations were performed, which includes the effects of the z-dependent electron effective mass, dielectric constant, and the nonparabolic dispersion. The strain effect is also taken into consideration by the deformation theory. In addition, the calculated optical absorption spectra included the many-body depolarization and excitonlike shifts. \textcopyright{} 1996 The American Physical Society.

Self-consistent determination of the band offsets in InAsxP1-x/InP strained-layer quantum wells and the bowing parameter of bulk InAsxP1-x.

Low- and room-temperature optical absorption spectra are presented for a series of $\mathrm{In}{\mathrm{As}}_{x}{\mathrm{P}}_{1\ensuremath{-}x}/\mathrm{InP}$ strainedlayer multiple quantum well structures ($0.11<~x<~0.35$) grown by low-pressure metal-organic vapor phase epitaxy using trimethylindium, tertiarybutylarsine, and phosphine as precursors. The well widths and compositions in these structures are exactly determined from the use of both high-resolution x-ray diffraction and transmission electron microscopy on the same samples. The absorption spectra are then analyzed by selfconsistently fitting, for the five samples, the excitonic peak energy positions with transition energies determined from a solution to the Schr\"odinger equation in the envelope function formalism using the well-known Bastard/Marzin model [J. Y. Marzin et al., in Semiconductors and Semimetals, edited by Thomas P. Pearsall, (Academic, New York, 1990), Vol. 32, p. 56]. From these self-consistent fits, both the bowing parameter of bulk unstrained $\mathrm{In}{\mathrm{As}}_{x}{\mathrm{P}}_{1\ensuremath{-}x}$ and the band offsets of the heterostructures are deduced self-consistently. The conduction-band offsets thus determined represent 75%\ifmmode\pm\else\textpm\fi{}3% of the total strained band-gap differences at both low (liquid He) and room temperatures. These values of the band offsets are consistent with the predictions of the quantum dipole model [J. Tersoff, Phys. Rev. B 30, 4874 (1984)]. The values determined for the bowing parameters are found to differ slightly between 0.10\ifmmode\pm\else\textpm\fi{}0.01 eV at low temperature and 0.12\ifmmode\pm\else\textpm\fi{}0.01 eV at room temperature.

Visible light emitting [formula omitted] superlattices

Six-period superlattices of Si SiO 2 have been grown at room temperature using molecular beam epitaxy. With this mature technology, the ultra-thin (1–3 nm) Si layers were grown to atomic layer precision. These layers were separated by ∼1 nm thick SiO 2 layers whose thickness was also well controlled by using a rate-limited oxidation process. The chemical and physical structures of the multilayers were characterized by cross-sectional TEM, X-ray diffraction, Raman spectroscopy, Auger sputter-profile, and X-ray photoelectron spectroscopy. The analysis showed that the Si layer is free of impurities and is amorphous, and that the SiO 2 Si interface is sharp (∼0.5 nm). Photoluminescence (PL) measurements were made at room temperature using 457.9 nm excitation. The PL peak occurred at wavelengths across the visible range for these multilayers. The peak energy position E was found to be related to the Si layer thickness d by E (eV) = 1.60+0.72 d −2 in accordance with a quantum confinement mechanism and the bulk amorphous-Si band gap.

Optical studies of acceptor centre doped [formula omitted] quantum wells

We present a theoretical and experimental study of the optical properties of acceptor centre doped quantum wells. We have performed theoretical calculations for the dependence of the band structure with doping level. Steady state photoluminescence and photoluminescence excitation results are compared with theoretical calculations involving exchange and correlation effects for the electron-hole system and the interaction between charge carriers and acceptor ions. We have studied the intensity, energy peak position, and broadening effects for excitons at doping level between 10 8 and 10 13 cm −2. Theoretical calculations that only consider band filling effects are not sufficient to describe the effect on the band structure due to the doping. A much better agreement is achieved when exchange and correlation effects for the electron-hole system are taken into account. Excitons can still be detected at high hole concentrations, above the degenerated limit. They survive due to the inefficiency of screening in the two-dimensional system.

Glycine Adsorption on Pt(111) in the Monolayer and Multilayer Regime

Glycine (GL) overlayers of varying thickness were deposited in situ on the clean Pt(111) surface by evaporating commercially available glycine powder. The temperature-stabilized evaporation source, made of Cu, was kept at 420 K during evaporation. The distance between Pt and the evaporation source was about 240 mm. The deposition rate and the total amount of glycine deposited were monitored by a quartz crystal microbalance that could be moved to intersect the GL beam approximately 40 mm downstream compared to the Pt position. The total amount of glycine in the reproduced spectra was 34 (~0.5 ML) and 340 ng/cm2 (~ 5 ML), respectively. We discuss the spectra with reference to both the neutral and zwitterionic states. There are two glycine-related C 1s peaks at both low and high GL coverages and a shoulder at ~ 285 eV most probably due to partial decomposition of glycine inside the evaporation source, at least for a thicker GL layer. The C 1s peak at lower binding energy is usually attributed to the C 1s carbon, while the peak at higher BE is supposed to stem from the carboxyl group. The energy of the peaks shifts with coverage, mainly due to the differences in charge transfer between Pt-GL (low coverage) compared to the GL-GL (high coverage). Slight charging of the sample (3.7 meV/ML) takes place, but results in a virtually uniform shift of all the GL levels involved. In the N 1s spectral region there appear two different N 1s components. The intensity of the peak at lower BE levels off with increased coverage from ~25% of the total N 1s intensity at low coverage to ~8% at higher coverages. The energy position of this lower BE peak is characteristic of NH2-like bonding. The position of the second N 1s peak suggests NH3+-like bonds. At high GL coverages the N 1s peak at low BE, and a C 1s shoulder at 285 eV, stem mainly from a slight decomposition of GL inside the evaporation source (below 8%). At low glycine coverages (<1 ML) there exist two different GL states on the surface: a majority of the amino acid molecules form zwitterions, while the remaining part is either neutral or decomposes into fragments some of which contain the NH2 group.

Occupied electronic states of CaSi2 and CaSi: Soft-x-ray-fluorescence spectroscopy.

The Ca ${\mathit{L}}_{2,3}$ and Si ${\mathit{L}}_{2,3}$ fluorescence spectra for ${\mathrm{CaSi}}_{2}$ and CaSi are studied. These spectra provide s and d partial density-of-states (PDOS) information for the Ca and Si atoms. The measured PDOS's are in good agreement with available calculations. Using monochromatized x rays to excite core electrons to localized Ca d states near threshold produces resonant recombination fluorescence peaks for the ${\mathit{L}}_{3}$ and ${\mathit{L}}_{2}$ edges of Ca in both compounds. In CaSi, with resonant excitation, inelastic Raman peaks are also observed. The energy position of the inelastic peaks indicates that the creation of the core hole shifts the Ca d states by several eV. The intensity of the resonance peaks indicates the degree of localization of the Ca d states, which is reduced by their participation in the bonding of the silicides. The empty Ca d states are found to be quite localized in CaSi, and less so in ${\mathrm{CaSi}}_{2}$.

Dynamics of charge carriers in cuprates

Detailed photoinduced infrared absorption studies of semiconducting Y 1Ba 2Cu 3O 6+y (y<0.2) and La 2CuO 4 were carried out. We observed two broad absorptions, one at ∼ 0.13 eV and the other at ∼ 0.62 eV in the photoinduced absorption spectrum of Y 1Ba 2Cu 3O 6+y in contrast to the previous photoexcitation results. We found that the lower energy peak positions in both Y 1Ba 2Cu 3O 6+y and La 2CuO 4 abruptly change at T - T c of the corresponding superconducting phase. The amount of energy shift seems to be related to the pairing energy. Carrier recombination dynamics studies suggest that the ground state of photocarriers in the CuO 2 plane at T < T c is remarkably different from that observed a T > T c.

Piezooptic examination of bound exciton recombination in uniaxially strained CdTe

Energy position and radiation intensity of the bound exciton annihilation lines in CdTe crystals have been obtained experimentally for the deformation range up to 2 kbar and for various directions of uniaxial compression. The nonlinear dependence of the energy peak position and nonmonotonic dependence of radiation intensity of the excitons bound to neutral acceptors on deformation was observed. The effective quenching of the emission of the acceptor-bound exciton intensity was found in the range of high pressures. Theoretical treatment takes into account the competition of two main recombination channels, namely Auger and radiative ones.