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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]

The growth mode and interface morphology in several InAs/GaAs samples have been investigated using photoreflectance. Experimentally derived energies for optical transition from the InAs were consistent with those seen in a simple square-well envelope-function scheme. Quantum well spectral features widen and vanish for L=2 ML, indicating the disappearance of the InAs 2D layer in favour of the nucleation of large quantum dots.

InAs quantum dots are self-aggregate at all values of the InAs layer thickness, with their density increasing as InAs nominal coverages increase. Transverse transmission electron microscopy also reveals that these quantum dots have mostly small base angles. Photoluminescence (PL) and PL excitation measurements of the optical properties of InAs/GaAs further show that a broad PL band is present in all samples. A narrow PL band is also observed for thin coverages.

Different experimental conditions are employed to monitor the stationary and time-resolved radiative emission from the well to analyze tunneling from near-surface quantum well to surface states in Al0.3Ga0.7As/GaAs multistructures. Electrons and holes exhibit separate tunneling before their binding in the exciton complex. The observations are explained by the advanced unified defect model. Hydrogen passivation eliminates the recombination at the surface.

Research was conducted on the energy levels of complexes formed by Ga vacancies and deuterium atoms using low-temperature photoluminescence. The datawas limited to a scenario wherein GaAs binds itself to one or more D atoms. Results revealed the presence of optical emissions from the deep acceptor states. D was also found to behave as a donor permittting internal donor-to-vacancy optical transitions.

Photoluminescence experiments were used to investigate hydrogen activated radiative states in GaAs/GaAlAs heterostructures and InGaAs/GaAs multiquantum wells. The results showed that the density of impurities and defects determined the level of volume incorporation of hydrogen. At moderate hydrogen treatment, novel emission bands and passivation of shallow acceptors were observed. Heavy hydrogen treatment produced a deep structure.

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]

The variation of the band gap energy of III-N-V semiconductors induced by hydrogen incorporation is the most striking effect that H produces in these materials. A special emphasis is given here to the combination of N-activity passivation by hydrogen with H diffusion kinetics in dilute nitrides. Secondary ion mass spectrometry shows an extremely steep (smaller than 5 nm/decade) forefront of the H diffusion profile in Ga(AsN) under appropriate hydrogenation conditions. This discovery prompts the opportunity for an in-plane nanostructuring of hydrogen incorporation and, hence, for a modulation of the material band gap energy at the nanoscale. The properties of quantum dots fabricated by a lithographically defined hydrogenation are presented, showing the zero-dimensional character of these novel nanostructures. Applicative prospects of this nanofabrication method are finally outlined. [ABSTRACT FROM AUTHOR]

Photoluminescence and optically detected magnetic resonance techniques are utilized to study defect properties of GaNP and GaNAs alloys subjected to post-growth hydrogenation by low-energy sub-threshold ion beam irradiation. It is found that in GaNP H incorporation leads to activation of new defects, which has a Ga interstitial (Gai) atom at its core and may also involve a H atom as a partner. The observed activation critically depends on the presence of N in the alloy, as it does not occur in GaP with a low level of N doping. In sharp contrast, in GaNAs hydrogen is found to efficiently passivate Gai-related defects present in the as-grown material. A possible mechanism responsible for the observed difference in the H behavior in GaNP and GaNAs is discussed. [ABSTRACT FROM AUTHOR]

Dilute nitride GaAs1-xNx layers have been grown by molecular beam epitaxy with nitrogen concentration ranging from 0.2% to 0.8%. These samples have been studied before and after hydrogen irradiation by using standard deep level transient spectroscopy (DLTS) and high resolution Laplace DLTS techniques. The activation energy, capture cross section and density of the electron traps have been estimated and compared with results obtained in N-free as-grown and H-irradiated bulk GaAs. [ABSTRACT FROM AUTHOR]

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]

The effects of hydrogen incorporation on carrier relaxation and recombination efficiencies in a large series of InAs self-assembled quantum dot structures deposited on InGaAs lower confining layers with different thicknesses and compositions have been addressed. With increasing H dose we observe an improvement in the radiative efficiency. By comparing steady state and time resolved photoluminescence measurements, it is established that the H passivation does not enhance the relaxation and capture efficiencies, but instead directly improves the emission yield from carriers in the dots. We therefore conclude that the H-passivated defects are located nearby, or even inside, the dots. [ABSTRACT FROM AUTHOR]

Focuses on a study which examined the tunneling mechanism of electrons and holes to surface states from near-surface Al[sub0.3]Ga[sub0.7]As/GaAs quantum wells, using steady-state and time-resolved photoluminescence spectroscopy. Introduction to tunneling mechanism; Experimental procedure; Results and discussion.

Investigates the energy levels of the complexes formed by gallium vacancies binding deuterium atoms by low-temperature photoluminescence. Possible GaAs configurations for a gallium vacancy binding hydrogen atoms; Characteristics of the emission bands in deuterated GaAs; Example of Gaussian deconvolution of the emission bands.

Focuses on Fourier transform of light-beam-induced current profiles expressed in a closed form. Use of standard minimization procedures on a personal computer; Influence of the experimental errors on the estimate of the diffusion length and of the recombination velocity; Procedure of fitting experimental data by standard minimization techniques.

Presents a study which proposed that the asymmetry observed in light and electron beam induced current (LBIC-EBIC) profiles is accounted for by a finite value for the angle ϑ between the grain boundary and the normal to the cell surface. Solution to the carrier diffusion differential equation in the case of a point source; Description of the normalized experimental EBIC profile; Details on the normalized experimental LBIC profile and best-fitting curve.

The effect of the order-disorder transition on the band gap of kesterite Cu2ZnSnS4, an interesting material for solar cells, has been investigated by optical spectroscopy. The band gap energy (Eg) decreases continuously with increasing annealing temperature, Ta, and reaches its minimum at Ta~273 °C. Eg is about 200 meV higher in the most ordered state, than in the fully disordered state. Its value and the transition kinetic depend on the sample stoichiometry. A simplified model able to explain the order degree and stoichiometry effects on the Eg value is developed. Ordering results in narrower Raman peaks without affecting the shape of the photoluminescence spectrum-- except for the change in Eg--or the characteristic energy of the exponential tail below the fundamental absorption edge. Although a prolonged annealing increases the order degree, the material properties are still influenced by residual disorder as well as by defects related to the offstoichiometry composition. [ABSTRACT FROM AUTHOR]

We show that the n-type conductivity of the narrow band gap In(AsN) alloy can be increased within a thin (--100 nm) channel below the surface by the controlled incorporation of H-atoms. This channel has a large electron sheet density of ~1018m-2 and a high electron mobility (μ > 0.1 m²V-1s-1 at low and room temperature). For a fixed dose of impinging H-atoms, its width decreases with the increase in concentration of N-atoms that act as H-traps thus forming N-H donor complexes near the surface. [ABSTRACT FROM AUTHOR]