We have evaluated the Burstein-Moss ͑BM͒ shift at 300 K in seven samples of n-In 0.53 Ga 0.47 As (1.3 ϫ10 16 рnр3.9ϫ10 19 cm Ϫ3 ) lattice matched to InP using spectral ellipsometry in the range of 0.4-5.1 eV. The data have been fitted over the entire spectral range to a model reported by Holden et al. ͓in Thermphotovoltaic Generation of Electricity, edited by T. J. Coutts, J. P. Brenner, and C. S. Allman, AIP Conf. Proc. No. 460 ͑AIP, Woodbury, NY, 1999͒, p. 39͔, based on the electronic energy-band structure near critical points plus relevant discrete and continuum excitonic effects. A Fermi-level filling factor in the region of the fundamental gap has been used to account for the BM effect. While our data exhibit nonparabolic effects, with a blueshift of 415 meV for the most highly doped sample, we did not observe the Fermi-level saturation at 130 meV for nу10 19 cm Ϫ3 reported by Tsukernik et al. . Our BM displacements are in agreement with a modified full-potential linearized augmented-plane-wave calculation ͓G. W. Charache et al., J. Appl. Phys. 86, 452 ͑1999͔͒ plus possible band-gap-reduction effects.The study of the Burstein-Moss ͑BM͒ effect in n-In 0.53 Ga 0.47 As lattice matched to InP is important from both fundamental and applied points of view. Recently Tsukernik et al. 1 presented an investigation of the BM shift in this material based on thermionic emission and diffusion over a barrier and concluded that the BM change saturates at about 130 meV for nу10 19 cm Ϫ3 . This observation was explained as a ''Fermi-level saturation;'' based on their results the authors called for a reexamination of existing theories. In contrast, Charache et al. 2 and Holden et al. 3 did not observe such a Fermi-level saturation in heavily doped n-In 0.66 Ga 0.34 As. Structures based on highly n-doped In 0.53 Ga 0.47 As materials have been used for several kinds of semiconductor devices such as heterojunction bipolar transistors, 4 resonant-tunneling devices, 5 and Bragg reflectors for surface-emitting lasers. 6 For these kinds of applications it is highly desirable to have information about the position of the Fermi level relative to the conduction-band edge.We present a study of the BM effect at 300 K in seven samples of n-In 0.53 Ga 0.47 As (1.3ϫ10 16 рnр3.9ϫ10 19 cm Ϫ3 ) lattice matched to InP using spectral ellipsometry. The data have been fitted using a comprehensive model 3,7 based on the electronic energy-band structure near critical points plus relevant discrete and continuum excitonic effects. The BM shift at the direct gap was accounted for using a Fermi-level filling factor in addition to the discrete and continuum excitonic terms. 3 The Fermi-level alteration exhibits nonparabolic effects. However, in contrast to Ref. 1, we did not observe a Fermi-level saturation. Our results exhibit a blueshift of 415 meV for the highest doped sample (nϭ3.9 ϫ10 19 cm Ϫ3 ). The BM displacements of this work are in agreement with a modified full-potential linearized augmented-plane-wave ͑FLAPW͒ calculation 2 plus possible band-...
We demonstrate that nanomechanically stamped substrates can be used as templates to pattern and direct the self-assembly of epitaxial quantum structures such as quantum dots. Diamond probe tips are used to indent or stamp the surface of GaAs(100) to create nanoscale volumes of dislocation-mediated deformation, which alter the growth surface strain. These strained sites act to bias nucleation, hence allowing for selective growth of InAs quantum dots. Patterns of quantum dots are observed to form above the underlying nanostamped template. The strain state of the patterned structures is characterized by micro-Raman spectroscopy. The potential of using nanoprobe tips as a quantum dot nanofabrication technology are discussed.
The interband transitions of a single quantum well structure of Zn0.53Cd0.47Se/Zn0.27Cd0.23Mg0.50Se (lattice matched to InP) were evaluated using contactless electroreflectance at room temperature. From a comparison of the measured optical transitions with those calculated using the envelope function approximation we determined that the conduction band offset for this system is given by the parameter Qc=ΔEc/ΔE0=0.82±0.02, which yields ΔEc of 590 meV. Such a large conduction band offset may be useful for the design of quantum cascade lasers and other devices based on intersubband transitions.
Using a rotating analyzer spectroscopic ellipsometer, we have investigated the complex dielectric function of a series of ternary BexZn1−xTe thin films in the energy range between 0.7 and 6.5 eV for alloy concentrations between x=0.0 and x=0.52. After determining the alloy concentrations using x-ray diffraction and photoluminescence techniques, a standard inversion technique was used to obtain the optical constants from the measured ellipsometric spectra. Analyzing the second derivative of both the real and the imaginary parts of the dielectric constant, we have deduced the critical point parameters corresponding to the electronic transitions in the Brillouin zone. We find that the energy of the critical points with respect to Be concentration does not show any bowing effects unlike many other II–VI semiconductor ternary alloys.
The optical constants ε(E)[=ε1(E)+iε2(E)] of two epitaxial layers of GaInAsSb/GaSb have been measured at 300 K using spectral ellipsometry in the range of 0.35–5.3 eV. The ε(E) spectra displayed distinct structures associated with critical points (CPs) at E0 (direct gap), spin-orbit split E0+Δ0 component, spin-orbit split (E1,E1+Δ1) and (E0′,E0′+Δ0′) doublets, as well as E2. The experimental data over the entire measured spectral range (after oxide removal) has been fit using the Holden model dielectric function [Holden et al., Phys. Rev. B 56, 4037 (1997)] based on the electronic energy-band structure near these CPs plus excitonic and band-to-band Coulomb-enhancement effects at E0, E0+Δ0, and the E1, E1+Δ1 doublet. In addition to evaluating the energies of these various band-to-band CPs, information about the binding energy (R1) of the two-dimensional exciton related to the E1, E1+Δ1 CPs was obtained. The value of R1 was in good agreement with effective mass/k⋅p theory. The ability to evaluate R1 has important ramifications for recent first-principles band-structure calculations which include exciton effects at E0, E1, and E2 [M. Rohlfing and S. G. Louie, Phys. Rev. Lett. 81, 2312 (1998); S. Albrecht et al., Phys. Rev. Lett. 80, 4510 (1998)]. The experimental absorption coefficients in the region of E0 were in good agreement with values obtained from a linear interpolation of the end-point materials. Our experimental results were compared to a recent evaluation and fitting (Holden model) of the optical constants of GaSb.
Abstract. ZrO2 waveguides are prepared by the sol-gel process from a solution containing zirconium n-propoxide and acetylacetone in propanol-2. Structural characterizations are investigated for different annealing temperatures using suitable techniques including Waveguide Raman Spectroscopy, Electron Microscopy and Atomic Force Microscopy. Films are amorphous at 300~ and the pure ZrO2 tetragonal crystalline phase appears beyond 400~ Crystallized films present a dense, uniform and polycrystalline structure made up by randomly oriented nanocrystallites, the diameter of which increases from 38/~ at 400~ to 53/~ at 600~ Waveguides are at least monomode TE0 at 632.8 nm. At this wavelength, optical losses are about 0.8 4-0.2 dB/cm for amorphous layers and increase up to 2.5 4-0.4 dB/cm for 600~ heat-treated waveguides.
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