We have grown self-assembled InAs quantum dots embedded in the center of an InGaAs quantum well by molecular-beam epitaxy. Using electron-beam lithography and wet etching techniques, small mesas with only a few quantum dots were fabricated. At room temperature, the quantum dots have an emission wavelength of 1.3 μm. By photoluminescence spectroscopy at low temperatures, we observe the emission lines of excitons and biexcitons in single-dot structures. The assignment of exciton and biexciton recombination is based on the characteristic excitation intensity dependence of these states. A biexciton binding energy of about 3.5 meV is obtained for the present dots.
Small mesa structures with only a few self-assembled InAs dashes for optical studies were realized by electron-beam lithography and etching techniques. The heterostructure was grown by molecular-beam epitaxy lattice-matched to an InP substrate and consists of an In0.53Ga0.23Al0.24As layer embedding in the center 3.3 monolayers of InAs. By self-assembly InAs dashes were formed. At low temperatures, narrow emission lines associated with electron-hole pairs confined in single dashes are observed. Biexciton transitions with typical binding energies of about 3.5 meV are found. The diamagnetic shift and the Zeeman splitting of single excitons are studied in magnetic fields up to 8 T in Faraday configuration. A large variation of the exciton g factor with the emission energy of quantum dashes is observed.
Self assembled InAs quantum dashes were grown by molecular beam epitaxy on In 0.53 Ga 0.23 Al 0.24 As lattice matched to InP. Using electron beam lithography and wet etching single dash structures were isolated for spectroscopic studies. At low temperatures emission lines associated with excitons and biexcitons confined in single dashes were observed. The Zeeman splitting of excitons are studied in magnetic fields up to 8 T in Faraday configuration. Corresponding g-factors vary between 1.5 to 2.2.1 Introduction Single self-assembled semiconductor quantum dots represent an interesting system to study physical properties of three dimensionally confined exciton systems [1][2][3][4]. Most investigations were done with quantum dots with emission wavelength below 1 µm. Here Si based CCDs have been used to study the electronic structure of excitons with previously not available spectral resolution [5][6][7][8][9][10]. Recently, InAs quantum dots emitting in the telecom wavelength ranges of 1.3 and 1.5 µm have become available on GaAs and InP substrates [11][12][13][14]. These dots have been used to realize novel laser structures [15,16] as well as to obtain information on ground and excited level transitions by optical spectroscopy on large ensembles. The photoluminescence of dash ensembles is rather broad (several 10's of meV) due to size and composition fluctuations within the ensemble. This inhomogeneous broadening prevents the observation of important parameters like exchange energies or biexciton binding energies. To determine these quantities in detail it is crucial to isolate single dashes.Here we report on the optical spectroscopy of single quantum dashes grown by molecular beam epitaxy on In 0.53 Ga 0.23 Al 0.24 As. Small mesas were fabricated by electron beam lithography and wet etching. At low temperatures in the photoluminescence spectra narrow emission lines appear and are associated with excitons and biexcitons confined in single quantum dashes. Applying magnetic fields up to 8 T we determined effective g-factors ranging from 1.5 to 2.2.
Self assembled InAs quantum dots embedded in an InGaAs quantum well were grown by molecular beam epitaxy. At room temperature these dots in a well (DWELLS) have an emission wavelength of 1.3 µm. Small mesas with lateral sizes down to 200 × 200 nm 2 were fabricated by electron beam lithography and etching techniques. By photoluminescence spectroscopy at low temperatures we observe narrow lines, which we attribute to excitons and excitonic molecules. Biexciton binding energies ranging between 3.5-5 meV are found.1 Introduction There has been considerable interest in the development of gain material with layers of self assembled quantum dots emitting at telecommunication wavelength windows (1.3 and 1.55 µm) [1 -2]. For emission at 1.3 µm the InAs dots are usually embedded in In x Ga 1-x As layers, according to the dot in a well (DWELL) concept [3]. Up to now most investigations of DWELLs are related to semiconductor lasers or to the optical properties of dot ensembles. In contrast, there exists no information on the spectral characteristics of single dots.We have grown self assembled InAs quantum dots embedded in the center of an In 0.15 Ga 0.85 As quantum well by molecular beam epitaxy. Using electron beam lithography and wet etching techniques small mesas with only a few quantum dots were fabricated. At room temperature the quantum dots have an emission wavelength of 1.3 µm. By photoluminescence spectroscopy at low temperatures, we observe the emission lines of excitons and biexcitons in single dots. The assignment of exciton and biexciton recombination is based on the dependence of these states on the characteristic excitation power intensity. Biexciton binding energies ranging from 3.5 -5 meV are obtained for the present dots. Our studies demonstrate that single quantum dot spectroscopy can be carried out far beyond the Si CCD sensitivity range using InGaAs array detectors. This extends the number of systems accessible for single dot studies considerably, permitting, e.g., the study of single InAs/InAlGaAs/InP dashes or GaSb dots.
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