Abstract
We investigate a hybrid system containing an In0.53Ga0.47As quantum well (QW), separated by a thin 2 nm In0.53Ga0.23Al0.24As barrier from 1.55 µm emitting InAs quantum dots (QDs), grown by molecular beam epitaxy on an InP substrate. Photoreflectance and photoluminescence (PL) spectroscopies are used to identify optical transitions in the system, with support of 8-band kp modelling. The main part of the work constitute the measurements and analysis of thermal quenching of PL for a set of samples with different QW widths (3–6 nm). Basing on Arrhenius plots, carrier escape channels from the dots are identified, pointing at the importance of carrier escape into the QW. A simple two level rate equations model is proposed and solved, exhibiting qualitative agreement with experimental observations. We show that for a narrow QW the escape process is less efficient than carrier supply via the QW due to the narrow barrier, resulting in improved emission intensity at room temperature. It proves that with carefully designed energy level structure, a hybrid QW/QD system can be used as an active region in telecom lasers with improved efficiencies.
Highlights
All the samples are grown by Molecular Beam Epitaxy on (100) oriented nominally undoped
The QW is separated by a 2 nm thin In0.53Ga0.23Al0.24As tunnelling barrier from InAs QDs
The thicknesses of respective layers are controlled by the growth parameters which were calibrated for thick InGaAs or InGaAlAs layers
Summary
The intensity of emission from the QDs is governed by: (i) the oscillator strength of the ground state transition, which should be very similar for all the samples due to identical dots growth conditions and the resulting wave functions’ overlap between the lowest energy electron and hole levels; (ii) the absorption of the excitation light, which again is comparable between the structures, being dominated by the identical wide InGaAlAs barriers present in all of them; (iii) carriers’ kinetics, i.e. the efficiency of the competing processes of carrier capture and escape, which are expected to depend on the coupling between the QW and QDs and details of the electronic structure. It demonstrates that with a careful design of energy level structure, a hybrid QW/QD system grown on InP substrates used as an active region of a QD-based laser, may offer improved performance for telecommunication applications
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