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The GaAs-like longitudinal-optical (LO) phonon frequency in hydrogenated GaAs1−xNx (x = 0.01) layers—with different H doses and similar low-energy irradiation conditions—was investigated by micro-Raman measurements in different scattering geometries and compared with those of epitaxial GaAs and as-grown GaAs1−xNx reference samples. A relaxation of the GaAs selection rules was observed, to be explained mainly on the basis of the biaxial strain affecting the layers. The evolution of the LO phonon frequency with increasing hydrogen dose was found to heavily depend on light polarization, thus suggesting that a linear relation between strain and the frequency of the GaAs-like LO phonon mode should be applied with some caution. Moreover, photoreflectance measurements in fully passivated samples of identical N concentration show that the blueshift of the GaAs-like LO frequency, characteristic of the hydrogenated structures, is dose-dependent and strictly related to the strain induced by the specific type of the dominant N-H complexes. A comparison of photoreflectance results with the finite element method calculations confirms that this dependence on the H dose is due to the gradual replacement of the N-2H complexes responsible for the electronic passivation of N with N-3H complexes, which are well known to induce an additional and sizeable lattice expansion. [ABSTRACT FROM AUTHOR]

Deposition of supersonic cluster beams was conducted to produce nanostructured carbon thin films. Pulsed arc cluster ion source modified was employed to achieve high fluxes and stability during the cluster generation. The films exhibited a low density network of nanometer-size particles and were graphite-like with numerous distorted bonds. However, the formation of structures based on sp3 bondings was not detected.

The quaternary alloy In(1-x)Ga(x)As(y)P(1-y) revealed four various vibration branches that correlated with the InAs-like, InP-like GaAs-like and GaP-like modes. The frequency position and frequency shifts of these vibration branches were determined. Metalorganic phase epitaxy facilitated the growth of In(1-x)Ga(x)As(y)P(1-y) on InP substrate.

The GaAs-like longitudinal optical phonon frequency in two hydrogenated GaAs1-xNx/GaAs1-xNx:H microwire heterostructures-with similar N concentration, but different H dose and implantation conditions-has been investigated by micro-Raman mapping. In the case of GaAs0.991N0.009 wires embedded in barriers where GaAs-like properties are recovered through H irradiation, the phonon frequency in the barriers undergoes a blue shift with respect to the wires. In GaAs0.992N0.008 wires embedded in less hydrogenated barriers, the phonon frequency exhibits an opposite behavior (red shift). Strain, disorder, phonon localization effects induced by H-irradiation on the GaAs-like phonon frequency are discussed and related to different types of N-H complexes formed in the hydrogenated barriers. It is shown that the red (blue) character of the frequency shift is related to the dominant N-2H (N-3H) type of complexes. Moreover, for specific experimental conditions, an all-optical determination of the uniaxial strain field is obtained. This may improve the design of recently presented devices that exploit the correlation between uniaxial stress and the degree of polarization of photoluminescence. [ABSTRACT FROM AUTHOR]

Research was conducted to examine the interband optical properties of molecular-beam epitaxially grown GaAs(sub 1-x)Sb(sub x) on GaAs substrates. The complex dielectric functions and the interband critical point energies, which are important not only in optical characterization and engineering of more complex heterostructures but also in achieving band structure parameters versus x, were provided. The analytical dependence of the critical point energies versus x allowed the interpolation of the dielectric functions and the optical functions for any composition x

The effect of hydrogen irradiation on the optical properties of GaAs1-xNx/GaAs heterostructures was investigated using photoreflectance and reflectance techniques. Systematic measurements performed on both as-grown and hydrogenated samples for N-concentrations ranging from 0.0% to 3.5% and for H-implanted doses from 3 × 1018 to 6 × 1018 ions/cm2 have shown that (a) the H-induced widening of the energy gap is accompanied by a decrease of the refractive index of the H-treated samples with respect to the as-grown ones, resulting in an index mismatch that can be as large as 2% in the subgap spectral region; and (b) the presence of compressive strain in fully passivated GaAsN determines a decrease of the refractive index even below that of GaAs that can be eliminated via moderate thermal annealing. These findings are promising for the development of heterostructures with planar geometry, in which the simultaneous confinement of both carriers and photons, even on a nanometric scale, can be obtained in a single step process. [ABSTRACT FROM AUTHOR]

We present a complete study both by experiments and by model calculations of quantum dot strain engineering, by which a few optical properties of quantum dot nanostructures can be tailored using the strain of quantum dots as a parameter. This approach can be used to redshift beyond 1.31 μm and, possibly, towards 1.55 μm the room-temperature light emission of InAs quantum dots embedded in InGaAs confining layers grown on GaAs substrates. We show that by controlling simultaneously the lower confining layer thickness and the confining layers’ composition, the energy gap of the quantum dot material and the band discontinuities in the quantum dot nanostructure can be predetermined and then the light emission can be tuned in the spectral region of interest. The availability of two degrees of freedom allows for the control of two parameters, which are the emission energy and the emission efficiency at room temperature. The InAs/InGaAs structures were grown by the combined use of molecular beam epitaxy and atomic layer molecular beam epitaxy; their properties were studied by photoluminescence and photoreflectance spectroscopies and by atomic force microscopy; in particular, by means of photoreflectance not only the spectral features related to quantum dots were studied but also those of confining and wetting layers. The proposed approach has been used to redshift the room-temperature light emission wavelength up to 1.44 μm. The optical results were analyzed by a simple effective-mass model that also offers a rationale for engineering the properties of structures for efficient long-wavelength operation. [ABSTRACT FROM AUTHOR]

One-dimensional photonic crystals made of (Si/SiO[sub 2])[sub m] multilayers with m = 2, … 8 have been grown on SiO[sub 2] 4-in. wafers by repeated polysilicon low-pressure chemical vapor deposition, oxidation, and wet etching steps. The poly-Si and SiO[sub 2] layers were about 220 and 660 nm thick, respectively, thus realizing λ/4 distributed Bragg reflectors. Spectroscopic ellipsometry in the 1.4-5 eV range was used to determine the dielectric function of poly-Si and the actual layer thicknesses, as well as to check the structural and compositional homogeneity of the structures. In order to measure the photonic crystal properties, specular reflectance and transmittance measurements were performed from 0.2 to 6 eV at different angles of incidence θ ≤ 50° and for transverse electric and transverse magnetic polarizations. The stop-bands characteristic of Bragg reflector multilayers appear up to the fifth order and become more pronounced with increasing m, reaching almost complete rejection for m = 4 periods. The experimental spectra were fitted by the transfer-matrix method, both versus θ and m. Moreover, the experimental stop bands of the finite multilayers matched the calculated photonic band gaps of an infinite one-dimensional photonic crystal very well. [ABSTRACT FROM AUTHOR]

The magnetic properties of Cd1-xMnxGa2Se4 crystal semiconductors grown by vapor phase transport were investigated. The results showed that there was a weak antiferromagnetic interaction between Mn++ ions. The magnetic suscpetibility exhibited a high-temperature Curie-Weiss behavior. In addition, the exchange integral constant was estimated to be approximately -1.5 K.

Presents a study which measured reflectance and transmittance spectra of p-type InP:Zn samples by Fourier transform infrared spectroscopy. Investigations on zinc diffusion into indium phosphide (InP); Details of experiments on undoped liquid encapsulated Czochralski InP; Description of spectra for the as-diffused and annealed samples.

Investigates the electrical and optical properties of gadolinium and erbium disilicide. Reason for the interest in transition-metal silicides; X-ray diffractometry used in identifying the silicide phases present in the films; Depth composition and film thickness of the silicides.

Presents an optical study of strained and relaxed epitaxial In[subx]Ga[1-x]As on gallium arsenide. Method of the study; Results and discussion; Conclusion.

Presents a study which examined the hafnium disilicide polycrystalline thin films, grown by coevaporation of hafnium and silicon, by electrical resistivity measurements, Hall voltage and optical reflectance. Composition and structure of the films; Electrical transport measurements; Measurement of the reflectance spectrum.

Analyzes interstitial oxygen content in heavily doped silicon samples. Background on the significance of oxygen in silicon; Application of the short baseline technique and by secondary-ion mass spectroscopy in analyzing the samples; Results and discussion.

Presents a study which examined the optical properties of germanium-implanted silicon as a function of germanium implantation affluence. Discussion on the electronic and structural properties of germanium-implanted silicon; Method used in silicon wafer implantation; Observation on the reflectivity spectra and dielectric functions for representative fluences; Discussion.