A. Bosacchi

Stokes shift in quantum wells: Trapping versus thermalization

Low temperature photoluminescence and photoluminescence excitation measurements have been performed in a set of

Self-aggregated InAs quantum dots in GaAs

{mathrm{In}}_{mathit{x}}

Thermoreflectance study of the direct energy gap of GaSb

{mathrm{Ga}}_{1mathrm{ensuremath{-}}mathit{x}}

Optical study of strained and relaxed epitaxial InxGa1−xAs on GaAs

As/GaAs samples with a different indium molar fraction, well width, growth conditions, and post-growth treatment. This has allowed to change in a controlled way the degree and source of disorder in the samples, thus resulting in an excitonic absorption linewidth varying between 1 and 18 meV, and an ensuing Stokes shift changing between zero and 8 meV. The conditions of validity of two different models relating the Stokes shift to the linewidth broadening have been established in terms of different regimes of disorder and temperature. A continuous transition between those regimes has been demonstrated. textcopyright{} 1996 The American Physical Society.

PHOTOREFLECTANCE VERSUS PHOTOLUMINESCENCE IN STRAIN INDUCED QUANTUM WELL WIRES

We present a detailed study, both structural and optical, of GaAs/InAs/GaAs heterostructures for InAs nominal coverages (L) ranging from 0.6 to 3 ML. Planar transmission electron microscopy (TEM) provides direct evidence of the presence of InAs quantum dots (QDs) for all values of L, with an increase in their density at high values of L. Transverse TEM shows also that those QDs have mostly small base angles. Accordingly, the evolution of the optical properties of InAs/GaAs is investigated by photoluminescence (PL) and PL excitation measurements (PLE). A broad PL band is observed in all samples, which is ascribed to the recombination of heavy-hole excitons in the InAs quantum dots, observed with TEM. For thin coverages (L⩽1.6ML), a narrow PL band is also observed, which is attributed to recombination of heavy-hole excitons in a two-dimensional (2D) InAs layer. The two bands shift to lower energy for increasing L. For L⩾1.6u2002ML, the QD band has a faster shift and exhibits a complex structure, while the excit...

Infrared reflectance study of n-type GaSb epitaxial layers

Abstract The complex refraction index and dielectric functions of GaSb bulk (both p and n -type) and MBE film were accurately determined from 0.0025 to 6 eV by using reflectance and ellipsometric spectroscopies. These functions, which satisfy the Kramers-Kronig causality relations, appear independent on the doping (≤2×10 17 cm −3 ) in the interband transition region. In particular, in comparison with previous data from literature, the E 0 fundamental gap is well evidenced for all the samples. Moreover, the optical functions around the gap are very different from those previously reported and the refractive index was modeled by a Sellmeier dispersion relation. The free-carriers instead strongly influence the far-infrared restrahlen region due to the phonon-plasmon coupling. In this range the optical functions were well fitted by Drude-Lorentz oscillators.

OPTICAL PROPERTIES OF INAS QUANTUM DOTS : COMMON TRENDS

Abstract We studied the optical properties of high quality GaSb layers, grown by molecular beam epitaxy, in the region of the fundamental gap E0 using thermoreflectance spectroscopy in the temperature range between 80 and 300 K. The experimental line-shapes were analyzed with a functional form model including excitonic effects. Taking advantage of the derivative-like nature of the thermoreflectance spectroscopy, an accurate determination of the temperature dependence of the energy gap E0(T) is obtained, which is well reproduced by the semi-empirical Varshni relation.

Exciton localization by potential fluctuations at the interface of InGaAs/GaAs quantum wells

Photoreflectance (PR) at different temperatures and spectroellipsometry (SE) at room temperature were used to study, in a systematic and complementary way, the optical response of a series of strained and relaxed InxGa1−xAs (x<0.15) epilayers. All the samples were grown by molecular‐beam epitaxy on GaAs, both with and without a GaAs cap layer, which in the thinnest samples determines a single‐quantum‐well configuration. The effects of the strain on the optical structures E0, E1, and E1+Δ1 observed in the 1.2–3.3 eV photon‐energy range were analyzed by fitting standard critical points (CP) line shapes to the PR and SE spectra. The CP experimental energies versus x were compared with the relations obtained in the framework of the elastic strain theory and, in the quantum‐well structures, of the envelope‐function scheme. The excellent agreement between experiment and theory allowed us to determine, independently and only by optical techniques, the strain e and the composition x values, which compare well wit...

Evolution of the Optical Properties of InAs/GaAs Quantum Dots for Increasing InAs Coverages

Photoreflectance vs photoluminescence measurements of stress-induced quantum wires, obtained by patterning an InGaAs layer pseudomorphic grown on a GaAs well in wire-shaped stressors, are presented and compared. An excellent agreement was found between the experimental results obtained with the two techniques about the lateral confinement of the carriers and evidence is given at room temperature of quantization in two directions by means of photoreflectance.