Quantum dot strain engineering of InAs∕InGaAs nanostructures

Abstract

We present a complete study both by experiments and by model calculations of quantum dot strain engineering, by which a few optical properties of quantum dot nanostructures can be tailored using the strain of quantum dots as a parameter. This approach can be used to redshift beyond 1.31μm and, possibly, towards 1.55μm the room-temperature light emission of InAs quantum dots embedded in InGaAs confining layers grown on GaAs substrates. We show that by controlling simultaneously the lower confining layer thickness and the confining layers’ composition, the energy gap of the quantum dot material and the band discontinuities in the quantum dot nanostructure can be predetermined and then the light emission can be tuned in the spectral region of interest. The availability of two degrees of freedom allows for the control of two parameters, which are the emission energy and the emission efficiency at room temperature. The InAs∕InGaAs structures were grown by the combined use of molecular beam epitaxy and atomic layer molecular beam epitaxy; their properties were studied by photoluminescence and photoreflectance spectroscopies and by atomic force microscopy; in particular, by means of photoreflectance not only the spectral features related to quantum dots were studied but also those of confining and wetting layers. The proposed approach has been used to redshift the room-temperature light emission wavelength up to 1.44μm. The optical results were analyzed by a simple effective-mass model that also offers a rationale for engineering the properties of structures for efficient long-wavelength operation.

Single quantum dot emission at telecom wavelengths from metamorphic InAs/InGaAs nanostructures grown on GaAs substrates

“…Metamorphic QDs allow single photon emission in the telecom windows; moreover, by engineering strain and band discontinuities, as proposed in Ref. 21, these nanostructures may have the potential for tuning emission and other single QD properties. …”

“…In structures with x = 0.30 LCL the emission is redshifted, due to reduction in QD strain and of QD-CL band discontinuities. 21 Thus, metamorphic nanostructures are able to emit one single photon into the second telecommunication window band ͑1.3 m͒ and the emission wavelength may be tuned by changing the composition of the LCL layers. Figure 2͑a͒ shows the power excitation dependence PL from the x = 0.15 sample.…”

Time resolved emission at 1.3 μm of a single InAs quantum dot by using a tunable fibre Bragg grating

“…Single QD emission in the long wavelength range in these structures has been demonstrated by us in reference [7]. The use of metamorphic InGaAs layer allows for the red-shift of the emission wavelength, thanks to the reduction of strain of QDs and band discontinuities [17], while the deposition of a subcritical coverage of InAs followed by annealing allows to obtain very low QD density (1 x 10 8 cm -2 ) for structures grown on metamorphic layers [18]. and XX 0 transitions, and the larger value for X + with respect to X 0 can be justified by a random carrier capture mechanism, as previously demonstrated for InAs single QDs emitting at 900-1000 nm [19], [7] In this way, continuous lines at the inset of figure 1.c represent the best fit to the measured integrated intensity variation by using a random population model [19].…”

Size dependent carrier thermal escape and transfer in bimodally distributed self assembled InAs/GaAs quantum dots

“…The QD effective recombination rate (r i ) is composed by the sum of radiative and non-radiative terms. The QD radiative recombination rate is obtained from the inverse of the measured PL decay time at 10 K. The activation energy of the thermal carrier capture into defect states has been set to $20 meV, 25,26 The main output parameter is the energy dependent i values plotted in Figure 7(a). We observe how i decreases with the QD size in both samples with almost the same trend, reflecting the carrier escape character.…”

“…It has been investigated attending to the available final states, i.e., QD excited states, 15,21 wetting layer, 4,6,7,13,20,22 GaAs barrier, 8,9,23 and impurity/defect levels. [23][24][25][26] Thermal escape can be also investigated attending to the nature of the particles being promoted to a higher energy state. 14 Depending on the model, the correlated (excitonic escape), 6,8,10,12,23 the uncorrelated electron-hole pair (ambipolar escape), 4,9,14 or just one of the carriers (unipolar escape) 15 can be considered.…”