T. Benyattou

Role of buffer surface morphology and alloying effects on the properties of InAs nanostructures grown on InP(001)

We show the role played by the buffer surface morphology and by alloying effects on the size, shape and lateral distribution of InAs nanostructures grown on InP(001) substrates by molecular beam epitaxy. Three buffers, viz., In0.53Ga0.47As, In0.52Al0.48As, and InP lattice matched on InP have been studied. Differences in nanostructure morphology and in carrier confinement have been evaluated by atomic force microscopy and by low-temperature photoluminescence measurements, respectively. Alongside the classical relaxation mode through two-dimensional/three-dimensional surface morphology change, a chemical relaxation mode has to be introduced as a competitive mode of relaxation of strained layers. This chemical relaxation mode, due to alloying between the InAs deposit and the buffer, is thought to be responsible for most of the observed differences in the InAs nanostructure properties.

Highly selective and widely tunable 1.55-μm InP/air-gap micromachined Fabry-Perot filter for optical communications

The authors report, for the first time, a highly selective and widely tunable optical filter at 1.55 /spl mu/m using a Fabry-Perot resonator with micromachined InP/air-gap distributed Bragg reflectors. The minimum resonance full-width at half-maximum (FWHM), as measured by microreflectivity experiments, is close to 0.4 mm (around 1.55 /spl mu/m) and is compatible with wavelength-division multiplexing specifications of optical telecommunications. The tuning range is 62 nm for a tuning voltage of 14 V. The FWHM is kept below 1 nm over a 40 nm tuning range.

Surface effects on shape, self-organization and photoluminescence of InAs islands grown on InAlAs/InP(001)

InAs nanostructures were grown on In0.52Al0.48As alloy lattice matched on InP(001) substrates by molecular beam epitaxy using specific growth parameters in order to improve island self-organization. We show how the change in InAs surface reconstruction via growth temperature from (2×4) to (2×1) and/or the use of InAlAs initial buffer surface treatments improve the island shape homogeneity (either as quantum wires or as quantum dots). Differences in island shape and in carrier confinement are shown by atomic force microscopy and by photoluminescence measurements, respectively. We point out that such shape amendments induce drastic improvements to island size distribution and discernible changes in photoluminescence properties, in particular concerning polarization.

From large to low height dispersion for self-organized InAs quantum sticks emitting at 1.55 μm on InP (001)

We show how the height dispersion of self-organized InAs/InP(001) quantum islands emitting at 1.55 μm was reduced by optimizing the epitaxial growth parameters. Low height dispersion was obtained when the InAs deposit thickness was much greater than the critical thickness for two-dimensional/three-dimensional growth mode transition, and when adatom surface diffusion was favored by increasing the growth temperature or reducing the arsenic pressure during the InAs growth. When these growth conditions are not respected, the multicomponent photoluminescence spectrum obtained is explained through the common interpretation of island height varying with monolayer fluctuation. In optimized growth conditions, the multicomponent spectrum obtained is interpreted as emission from fundamental and excited levels of InAs islands with low height dispersion. Transmission electron microscopy (TEM) imaging shows that these InAs islands are stick-like, 50–100 nm in length and 22±1.2 nm in width. Cross-sectional TEM reveals f...

Simulation of the capacitance–voltage characteristics of a single‐quantum‐well structure based on the self‐consistent solution of the Schrödinger and Poisson equations

The numerical self‐consistent solution of the coupled Schrodinger and Poisson equations is used to simulate the C–V characteristic of Schottky barrier heterostructures with a single quantum well (SQW). This model is applied to study n‐type SQW structures based on InGaAs/InAlAs. It has been shown from analysis of the C–V characteristics of a SQW structure that it is possible to extract information about the energy position of subband levels and the distribution of electron density in the QW. We have demonstrated that due to the two‐dimensional distribution of electron gas in the QW the apparent concentration profile NC–V–W derived from the C–V characteristic fails to describe the free electron density distribution in the QW layer. However, the number of the NC–V–W peaks indicates the quantity of electron subband levels in the QW situated below the Fermi level at zero reverse bias.

Bragg surface wave device based on porous silicon and its application for sensing

Results concerning a Bragg surface wave device based on porous silicon and intended for sensing application are reported. Existence of optical surface waves on Bragg structures is experimentally shown. Such device is expected to be very sensitive to the grafting of biological molecules. The authors demonstrate this sensing effect by grafting of amine chemical groups. The optical characterization using m-line spectroscopy shows that the increase of the coupling angle is about 20° after the amine grafting. The authors show that porosity is essential for reaching this high sensitivity.Results concerning a Bragg surface wave device based on porous silicon and intended for sensing application are reported. Existence of optical surface waves on Bragg structures is experimentally shown. Such device is expected to be very sensitive to the grafting of biological molecules. The authors demonstrate this sensing effect by grafting of amine chemical groups. The optical characterization using m-line spectroscopy shows that the increase of the coupling angle is about 20° after the amine grafting. The authors show that porosity is essential for reaching this high sensitivity.

1.54 μm room‐temperature electroluminescence of erbium‐doped GaAs and GaAlAs grown by molecular beam epitaxy

GaAs and GaAlAs double‐heterostructure light emitting diodes doped with erbium have been grown by molecular beam epitaxy. Both devices exhibit 1.54 μm electroluminescence (EL) at 300 K but the spectra obtained for GaAlAs:Er are much narrower than those of GaAs:Er. 1.54 μm EL has been detected for injection currents as low as 0.8 mA/cm2 and an external quantum efficiency of 10−6 has been found at 300 K. Preliminary data concerning the energy transfer from the injected carriers to the rare earth are provided.

Investigations of vertical cavity surface emitting laser by photoreflectance spectroscopy

We report photomodulated reflectance results on vertical cavity surface emitting laser structures. Photoreflectance spectra have been recorded under normal incidence at different temperatures between 9 and 300 K. The structure used is a λ cavity grown in the AlGaAs‐based system emitting at a wavelength near 800 nm. We show that photoreflectance is a unique noninvasive tool to measure accurately the quantum well transition and the cavity mode alignment: both features can be distinguished very well. Furthermore, this technique offers the opportunity to determine the electric field within the undoped region from Franz–Keldysh oscillations, and gives the Al composition of the barrier material in the cavity.

Design, simulation, and characterization of a passive optical add-drop filter in silicon-on-insulator technology

We present a passive novel optical add-drop filter incorporating microdisk resonators, in complementary metal-oxide-semiconductor compatible silicon-on-insulator technology, which enables a simple layout of complex optical networks-on-chip. The measured properties of the fabricated devices are in agreement with theory, established using the time-domain coupled mode theory and finite-difference time-domain simulations.

TIME-RESOLVED PHOTOLUMINESCENCE SPECTROSCOPY FROM ERBIUM-DOPED GA0.55AL0.45AS

Time‐resolved photoluminescence (PL) spectroscopy has been performed on erbium‐doped Ga0.55Al0.45As. We have investigated the 4I13/2→4I15/2 optical transition. The measured fluorescence lifetime is around 1.2 ms which is similar to values found for other erbium‐doped III‐V compounds. Studies as a function of temperature indicate nonradiative transitions characterized by thermal activation of 40 meV. With the help of two beam experiments we have confirmed the existence of Auger losses during the PL excitation and a model of the excitation process is proposed that accounts for the experimental results.