D. A. Tenne

Raman study of self-assembled InAs quantum dots embedded in AlAs: influence of growth temperature

Abstract Phonon spectra of self-assembled InAs quantum dots (QDs) in an AlAs matrix were studied by Raman spectroscopy. A series of InAs QDs was grown by molecular beam epitaxy at substrate temperatures varied in the range of 420–550°C. The observed asymmetric line shape of LO phonons in InAs QDs and its low-frequency shift with increasing excitation energy are explained by QD size distribution and phonon confinement in small-size dots. Phonons of the InAs wetting layer are also observed in the Raman spectra of QD structures. Two bands of interface phonons in the AlAs frequency region are attributed to phonons associated with two types of interfaces: the planar interface wetting layer/AlAs matrix and the three-dimensional QD/matrix interface. A comparison of the position and the line shape of phonon features of InAs QDs grown at different temperatures reveals that dots grown at low temperatures (∼420°C) have the smallest average size. Increasing the temperature leads to the formation of larger InAs islands. At temperatures higher than 520°C partial re-evaporation of InAs occurs.

Optical characterisation of PTCDA films grown on passivated semiconductor substrates

3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA) was deposited on passivated Si(111) and GaAs(001) surfaces using organic molecular beam deposition (OMBD). The growth of the PTCDA films was monitored in situ and on-line by means of Raman spectroscopy. In addition, ex situ infrared (IR) spectra were recorded in order to observe the non-Raman active modes. Raman and IR spectra reveal molecular vibrational modes, allowing us to characterize the structural quality of the PTCDA films and the interaction with the substrate.

Millisecond photoluminescence kinetics in a system of direct-bandgap InAs quantum dots in an AlAs matrix

Anomalously long millisecond kinetics of photoluminescence (PL) is observed at low temperatures (4.2–50 K) in direct-bandgap InAs quantum dots formed in an AlAs matrix. An increase in temperature leads to a decrease in the duration of PL decay down to several nanoseconds at 300 K, whereas the integral PL intensity remains constant up to 210 K. In order to explain the experimental results, a model is proposed that takes into account the singlet-triplet splitting of exciton levels in small quantum dots.

Raman spectroscopy: a powerful tool for characterisation of Ag/3,4,9,10-perylene-tetracarboxylic-dianhydride/GaAs heterostructures

Abstract The present contribution emphasises the capabilities of Raman spectroscopy for the characterisation of chemical and structural properties of thin organic films. As an example, a perylene derivative is presented, namely 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA). The focus will be directed to the Raman monitoring of dynamic processes. First, the PTCDA film formation on GaAs substrates by organic molecular beam deposition will be followed. The changes in the GaAs bands and PTCDA internal and external vibrational modes will be investigated as indicators for the interface formation. Secondly, the PTCDA internal modes will be monitored upon the deposition of silver onto the PTCDA/GaAs heterostructure.

Self‐Assembled Islands in the (Ga,Al)As/InAs Heteroepitaxial System Studied by Raman Spectroscopy

| References | Full Text: PDF (117k) | Related Articles | Citation Tracking Original Paper Self-Assembled Islands in the (Ga,Al)As/InAs Heteroepitaxial System Studied by Raman Spectroscopy D.A. Tenne , V.A. Haisler , A.K. Bakarov , A.I. Toropov , A.K. Gutakovsky , A.P. Shebanin , D.R.T. Zahn 2 Institute of Semiconductor Physics, 630090 Novosibirsk, Russia Institut für Physik, Technische Universität Chemnitz, D-09107 Chemnitz, Germany United Institute of Geology, Geophysics and Mineralogy, 630090 Novosibirsk, Russia email: D.A. Tenne (tenne@thermo.isp.nsc.ru)

The formation of inas quantum dotsin an aluminum oxide matrix

The formation of InAs quantum dots in an aluminum oxide matrix by selective oxidation of AlAs layers in an InAs/AlAs heterostructure is studied. According to the Raman spectroscopy data, the process of selective oxidation leads to stress relaxation in the InAs quantum dots and to the formation of amorphous arsenic at the boundary between oxidized and unoxidized regions.

Resonant Raman Scattering by Strained and Relaxed Ge Quantum Dots

Fundamental vibrations in Ge/Si structures with strained and relaxed Ge quantum dots (QDs) grown by molecular beam epitaxy were investigated using resonant Raman spectroscopy. Transmission electron microscopy experiments show that the strained Ge QDs are typical “hut clusters” with base size of 15nm and a height of 2nm. A two mode distribution in size (100200nm and 3-6nm) is found for relaxed QDs. The Raman efficiencies of the Ge optical phonons as a function of excitation energy reveal maxima at 2.35-2.41eV attributed to the E0 resonance in Ge QDs due to electronic confinement. The frequency positions of optical phonons localized in Ge “hut clusters” under non-resonant conditions correspond to fully strained Ge QDs while the frequency position of optical phonons in relaxed Ge QDs corresponds to the value in bulk Ge. With increasing excitation energy (2.5-2.7eV) the position of the Ge optical phonons shifts downwards due to size-confinement effect of optical phonons in strained and relaxed Ge QDs, indicating the presence of a QD size distribution in Ge dot structures.

Anisotropy of optical phonons in semiconductor superlattices: Raman scattering experiments

Experiments on Raman scattering in the “forward” geometry, permitting observation of anisotropy of the optical phonons, are performed on specially prepared short-period GaAs/AlAs superlattice structures with the substrates removed and the surfaces covered with an antireflective layer. The experimental data agree well with the computational results obtained for the angular dispersion of optical phonons in superlattices on the basis of a modified continuum model.

Mechanism of Recombination in InAs Quantum Dots in Indirect Bandgap AlGaAs Matrices

Photoluminescence kinetics in InAs quantum dots in indirect‐gap AlGaAs matrixes has been studied. It has been found that the duration of the photoluminescence decay at low temperatures greatly decreases from milliseconds down to nanoseconds with decreasing the AlAs fraction in the AlGaAs matrix. The experimental results are interpreted in the framework of a model that takes into account exchange splitting of excitonic levels in the quantum dots and the deviation of its shape from spheroid.

Model of photoluminescence of InAs quantum dots embedded in indirect band gap AlGaAs matrices

Photoluminescence kinetics in InAs quantum dots embedded in indirect-gap AlGaAs matrices has been studied. It has been found that the duration of the photoluminescence decay at low temperatures greatly decreases from milliseconds down to nanoseconds with decreasing the AlAs fraction in the AlGaAs matrix. The experimental results are interpreted in the framework of a model that takes into account an exchange splitting of excitonic levels in the quantum dots.