A large amount of work world-wide has been directed towards obtaining an understanding of the fundamental characteristics of porous Si. Much progress has been made following the demonstration in 1990 that highly porous material could emit very efficient visible photoluminescence at room temperature. Since that time, all features of the structural, optical and electronic properties of the material have been subjected to in-depth scrutiny. It is the purpose of the present review to survey the work which has been carried out and to detail the level of understanding which has been attained. The key importance of crystalline Si nanostructures in determining the behaviour of porous Si is highlighted. The fabrication of solid-state electroluminescent devices is a prominent goal of many studies and the impressive progress in this area is described.

The structural and luminescence properties of porous silicon

https://hal.archives-ouvertes.fr/hal-00120432/document

Raman Spectroscopy of Nanomaterials: How Spectra Relate to Disorder, Particle Size and Mechanical Properties

In this study, both the linear and nonlinear intersubband optical absorption coefficients and the refractive index changes are calculated for the uniform, triangular and Gaussian-like donor distribution. The Gaussian-like distribution differs from the Gaussian distribution other authors use. The electronic structure of n-type Si δ-doped GaAs has been theoretically calculated by solving the Schrodinger and Poisson equations self-consistently. Our results show that the location and the size of the linear and total absorption coefficients and refractive index changes depend on the donor distribution type. The shape of δ-effective potential profile and the subband properties are changed as dependent on the donor distribution model. Therefore, the variation of the absorption coefficients and refraction index changes, which can be appropriate for various optical modulators and infrared optical device applications can be smooth obtained by the alteration donor distribution model.

Nonlinear intersubband absorption and refractive index change in n-type δ -doped GaAs for different donor distributions

Quantum-dot-tagged reduced graphene oxide (QD-rGO) nanocomposites (left) internalized into targeted tumor cells display bright fluorescence from the QDs (right); by absorbing NIR radiation incident on the rGO and converting it into heat, they also cause simultaneous cell death and fluorescence reduction (bottom). The nanocomposite is thus capable of tumor imaging, photothermal therapy and in situ monitoring of treatment in progress.

https://ir.nctu.edu.tw:443/bitstream/11536/15766/1/000302014400012.pdf

Quantum-Dot-Tagged Reduced Graphene Oxide Nanocomposites for Bright Fluorescence Bioimaging and Photothermal Therapy Monitored In Situ

▪ Abstract Highly strained semiconductors grow epitaxially on mismatched substrates in the Stranski-Krastanow growth mode, wherein islands are formed after a few monolayers of layer-by-layer growth. Elastic relaxation on the facet edges, renormalization of the surface energy of the facets, and interaction between neighboring islands via the substrate are the driving forces for self-organized growth. The dimensions of the defect-free islands are of the order λB, the de Broglie wavelength, and provide three-dimensional quantum confinement of carriers. Self-organized In(Ga)As/GaAs quantum dots, or quantum boxes, are grown by molecular beam expitaxy (MBE) or metal-organic vapor phase epitaxy (MOVPE) on GaAs, InP, and other substrates and are being incorporated in microelectronic and opto-electronic devices. The use of strain to produce self-organized quantum dots has now become a well-accepted approach and is widely used in III–V semiconductors and other material systems. Much progress has been made in the ar...

Quantum dot opto-electronic devices

We investigated the temperature effect on exciton localization in self‐organized InAs quantum dots Quenching energy for excitons in reference quantum well and quantum dots was found to be 2 and 7 meV, respectively Thermoactivation energy of electron‐hole emission through a GaAs barrier in the quantum dots was measured as 46 meV We observed an unusual decrease of photoluminescence peak full width at half maximum with temperature, suggesting suppression of nonpredominant size quantum dot emissions due to carrier tunneling between nearby dots

Exciton localization and temperature stability in self‐organized InAs quantum dots

Optical characterization of strained InGaAs/GaAs quantum dots grown by molecular beam epitaxy on (001) and (n11)B, where n=1, 2, 3, 5, and 7 orientations is reported in this work. Quantum dot photoluminescence emission shows remarkable orientation effects, presented in peak shape, full width at half‐maximum, and integrated intensity. Quantum dots grown on the (711)B plane demonstrate high quantum efficiency: integrated photoluminescence ratio between quantum dots and quantum well is about 10. Our results indicate an enhancement of the quantum dots onset thermal quenching energy by a factor of 2.5 for all orientations. Activation energy for thermal stimulated electron–hole emission in quantum dots is 2–5 times higher than in quantum wells. Photoluminescence polarization measurements show strong in‐plane dependence caused by the quantum dots’ structural anisotropy.

High index orientation effects of strained self‐assembled InGaAs quantum dots

Interface vibrational modes localized at the apexes of pyramidal InAs self-assembled quantum dots embedded in GaAs were observed by resonance Raman scattering. The comparison of the frequency positions of the interface modes with those obtained theoretically reveals a strong influence of the strain. The strain calculated for the InAs/GaAs dots satisfactorily explains the strain-induced frequency shifts obtained for the interface modes. It is important to notice that the interface modes observed in this study can be found in any corrugated interfaces containing tips and cusps where they can be localized.

Raman study of interface modes subjected to strain in InAs/GaAs self-assembled quantum dots

Negative linear magnetoresistance of two-dimensional (2D) electrons have been found in a disordered array of antidots. The authors suggest that trajectories that roll along the array of antidots exist in a magnetic field. These trajectories have a mean free path larger than the average value for electrons with ordinary diffusion.

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Negative differential magnetoresistance and commensurability oscillations of two-dimensional electrons in a disordered array of antidots

We investigate periodically silicon δ‐doped GaAs sample grown by molecular‐beam epitaxy using magnetoresistance measurements. Transport measurements give evidence for quantum confinement of the electronic gas in the layer. Thomas–Fermi approximation is used in order to assess the various subband densities.

P. Basmaji

Papers

Exciton localization and temperature stability in self‐organized InAs quantum dots

High index orientation effects of strained self‐assembled InGaAs quantum dots

Raman study of interface modes subjected to strain in InAs/GaAs self-assembled quantum dots

Negative differential magnetoresistance and commensurability oscillations of two-dimensional electrons in a disordered array of antidots

Electronic transport in periodically δ‐doped GaAs layers