S. Martini

InAs/GaAs quantum dots optically active at 1.5 μm

InAs quantum dots grown by molecular-beam epitaxy on GaAs substrates are demonstrated to be suitable structures to achieve an optical emission in the 1.3–1.5-μm range. Their tuning towards such long wavelengths was made possible by combining an extreme reduction of the InAs growth rate and a fast growth of the GaAs cap layer at low temperature. Our results create perspectives for the fabrication of GaAs-based devices operating in the most important telecommunications window.

Influence of the temperature and excitation power on the optical properties of InGaAs/GaAs quantum wells grown on vicinal GaAs(001) surfaces

Photoluminescence experiments were performed as a function of temperature and excitation intensity in order to investigate the optical properties of In0.1Ga0.9As/GaAs quantum wells grown on vicinal GaAs(001) substrates with different miscut angles. The misorientation of the surface played an important role and influenced the intensity, efficiency, energy, and full width at half maximum of the optical emission, as well as the segregation of indium atoms. It is shown that at high temperature the optical properties of InGaAs quantum wells grown on vicinal substrates are slightly inferior to ones of the same structure grown a nominal surface because of the faster escape of the carriers.

Influence of the temperature on the carrier capture into self-assembled InAs/GaAs quantum dots

Photoluminescence (PL) spectroscopy and atomic-force microscopy (AFM) were used to investigate the size evolution of InAs quantum dots on GaAs(001) as a function of the amount of InAs material. Different families of islands were observed in the AFM images and unambiguously identified in the PL spectra, together with the signal of the wetting layer. PL measurements carried out at low and intermediate temperatures showed a thermal carrier redistribution among dots belonging to different families. The physical origin of this behavior is explained in terms of the different temperature dependence of the carrier-capture rate into the quantum dots. At high temperatures, an enhancement of the total PL-integrated intensity of the largest-sized quantum dots was attributed to the increase of diffusivity of the photogenerated carriers inside the wetting layer.

Real-time determination of the segregation strength of indium atoms in InGaAs layers grown by molecular-beam epitaxy

The surface segregation of indium (In) atoms was investigated during the growth of InGaAs layers by reflection high-energy electron diffraction (RHEED). We observed that the decay constant of the RHEED-oscillation amplitude during growth depends on the growth conditions and is related, in a very simple way, to the segregation coefficient of the In atoms in the InGaAs layers.

Influence of indium segregation on the RHEED oscillations during the growth of InGaAs layers on a GaAs(001) surface

The surface segregation of indium (In) atoms was investigated during the growth of InGaAs layers by reflection high-energy electron diffraction (RHEED). We showed that the strong damping of the RHEED oscillations usually observed during the deposition of InGaAs on GaAs was directly related to the presence of a population of In atoms at the surface of the sample originating from the segregation phenomenon in the InGaAs layers. We proposed a simple model to estimate the segregation coefficient R in situ and in real time from the RHEED oscillations. Our results were quantitatively confirmed by several RHEED measurements carried out under very different growth conditions and were in excellent agreement with data from the literature.

Optical response at 1.3 μm and 1.5 μm with InAs quantum dots embedded in a pure GaAs matrix

We demonstrated that the growth of InAs on GaAs at rates as low as 0.003 ML/s can be used to form quantum dots (QDs) that are optically active at 1.3 and 1.5 μm. The emission at 1.5 μm (at 300 K) originating from individual InAs QDs embedded in a pure GaAs matrix is close to the important telecom window at 1.55 μm. Such emission is related to a narrow distribution of islands with a height peaked around 15 nm as shown by atomic-force microscopy.

Ex-situ investigation of indium segregation in InGaAs/GaAs quantum wells using high-resolution x-ray diffraction

Calculations using the dynamical theory of diffraction together with a sample model which considers the segregation of indium atoms were employed to fit the high-resolution x-ray spectra of strained InGaAs/GaAs quantum wells grown by molecular-beam epitaxy. The segregation coefficients obtained from the best fits to the experimental data of samples grown at different temperatures are in excellent agreement with the expected values and confirm that x-ray diffraction is a valuable tool for the investigation of the segregation phenomenon.

Influence of illumination on the quantum mobility of a two-dimensional electron gas in si δ-doped GaAs/In0.15Ga0.85As quantum wells

A series of GaAs/InGaAs quantum wells with a silicon δ-doped layer in the top barrier was investigated by Shubnikov–de Haas measurements as a function of the illumination time of the samples. During the illumination process strong modifications of the electronic density and the quantum mobility of each occupied subband were observed. Based on self-consistent calculations, the dominant mechanism which caused the changes in the subband quantum mobilities with illumination was elucidated.

Low growth rate InAs/GaAs quantum dots for room-temperature luminescence over 1.3 μm

Abstract Uncapped InAs/GaAs quantum dots with average height around 15 nm were grown under the regime of ultra-low growth rates (

Step bunching in InGaAs/GaAs quantum wells grown by molecular beam epitaxy on GaAs(0 0 1) vicinal surfaces

In the present work, we investigated the influence of step bunching on the optical properties of InGaAs/GaAs quantum wells (QWs) grown by molecular beam epitaxy (MBE) on vicinal surfaces. Photoluminescence (PL) measurements showed a larger full width at half maximum (FWHM) of the emission coming from the QWs grown on the vicinal surfaces with respect to the nominal sample. Transmission-electron-microscopy (TEM) measurements revealed the presence of step bunches that clearly roughen the interfaces of the heterostructures and worsen the optical properties of the samples.