Tuning vertically stacked InAs/GaAs quantum dot properties under spacer thickness effects for 1.3��m emission (original) (raw)
Related papers
Optimizing the spacer layer thickness of vertically stacked InAs/GaAs quantum dots
Materials Science and Engineering: C, 2006
Vertically stacked multilayers of self-organized InAs/GaAs quantum dots (QDs) structures with different GaAs intermediate layer thicknesses varying between 2.8 and 17 nm are grown by solid source molecular beam epitaxy (SSMBE) and investigated by photoluminescence spectroscopy (PL). For 17 nm thick GaAs spacer, the PL spectra show two well separated features attributed to the formation of two QDs family with a bimodal size distribution indicating no correlation between the dots in different layers. In the meanwhile, the structures having thinner spacer thickness demonstrate single PL peaks showing an enhancement of high energy side asymmetrical broadening when increasing the excitation power. The corresponding emission energies exhibit a red shift when the spacer layer thickness decreases and correlated with the enhancement of the vertical electronic coupling as well as the rise of the QD's size in the upper layers induced by the build up of the strain field along the columns. The spacer thickness of 8.5 nm is found to yield the best optical properties. D
Nanotechnology, 2007
This work systematically investigated the optical and structural properties of multilayer electronic vertically coupled InAs/GaAs quantum dot (QDs) structures grown by molecular beam epitaxy for long-wavelength applications. A significant energy blue-shift in the photoluminescence (PL) spectra from 30-period InAs/GaAs QDs structures was observed as the GaAs spacer thickness was decreased. Transmission electron microscopy (TEM) and PL measurements indicated that the abnormal blue-shift can be attributed to the strain-driven In/Ga intermixing between QDs and spacer layers, which overcompensates for the effects of electronic and structural couplings between QD layers. Moreover, this study demonstrates that increasing the growth rate of InAs QDs can prevent intermixing. A PL emission wavelength of 1320 nm with strong luminescence at room temperature, which corresponds to an energy red-shift of 50 meV from that of the single QD layer sample, was achieved in a 10-period InAs/GaAs QD superlattice with a spacer thickness of 16 nm.
physica status solidi (a), 2003
InAs/GaAs vertically stacked self-assembled quantum dot (QD) structures with different GaAs spacer layer thicknesses are grown by solid source molecular beam epitaxy (SSMBE) and investigated by transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. An increase in the polarization anisotropy is observed when the spacer layer thickness decreases. For a 10 monolayer (ML) thick inter-dots GaAs spacer, the TEM image shows an increase in the QD size when moving to the upper layer accompanied by the generation of dislocations. Consequently, the corresponding temperature-dependant PL properties are found to exhibit an unusual behaviour. The main PL peak is quenched at a temperature around 190 K giving rise to a broad background correlated with the formation of a miniband in the growth direction due to the strong interlayer coupling. For a thicker GaAs spacer layer (30 ML), multilayer QDs align vertically in stacks with no apparent structural defects. Over the whole temperature range, the excitonic band energies are governed by the Varshni empirical relation using InAs bulk parameters and the PL line width shows a slight monotonic increase. For a thinner GaAs interlayer, the thermal activation energies of the carrier emission out of the quantum dots are found to be considerably small (about 25 meV) due to the existence of defects. By combining these structural and optical results, we can conclude that a thinner GaAs spacer has a poorer quality.
Superlattices and Microstructures, 2013
We examined self-organized InAs/GaAs bilayer quantum dot (BQD) structures grown by solid source molecular beam epitaxy. The two layers had an intermediate GaAs barrier/spacer layer (SL) varying between 75 Å and 200 Å thicknesses. The photoluminescence (PL) characteristics of the InAs/GaAs BQDs were investigated by varying three growth parameters: (i) growth rate (monolayers per second, ML/s) of active dot layer, (ii) deposition amount (ML) of InAs on active dot layer while keeping that on the seed layer constant, and (iii) GaAs SL thickness (Å A 0). Analysis of temperature-dependent PL data indicated an optimum SL thickness of 100 Å, for which the low-temperature PL emission peak is at 1.3 lm with a full width at half-maximum of 24.5 meV. BQD optimization was achieved with a slow (0.03 ML/s) rather than fast (0.3 ML/s) growth rate, and with a larger (3.2 ML) rather than smaller (2.5 ML) deposition of InAs on the active dot layer.
InAs/GaAs SK quantum dots stacking: Impact of spacer layer on optical properties
In this paper, we report the optical properties of vertically stacked multilayers of self-organized InAs/GaAs quantum dots QDs with different GaAs spacer layer thicknesses of 10 and 15 nm, using photoluminescence PL measurement. The 10 K PL spectrum exhibits double-emission peaks ambiguously identified in PL spectra where the excitation power dependence reveals that these emission peaks are attributed to fundamental ground state GS of large quantum dots in the low energy side, and first excited state 1ES transitions of large quantum dots in coincidence with fundamental ground state GS of smaller ones, in the high energy side. Both the excitation power dependence and the temperature dependence measurement results exhibited competition between the latter's optical transitions in the QDs, which becomes more prevalent at higher excitation powers. The main PL peak is quenched above 190 K, giving rise to "a 1D miniband", ascribed to the electronic coupling between QDs along the stacking direction and tuning the emission wavelength around 1.3 μm. Our results emphasize the Key role of the vertically stacked InAs/GaAs QDs structures with thin GaAs spacer layers in optimizing design for long-wavelength devices.
Tsinghua Science & Technology, 2010
Uncapped double stacked In 0.5 Ga 0.5 As quantum dots (QDs) with different spacer layer thicknesses were grown using metal-organic chemical vapour deposition (MOCVD). The precursors used for the growth of the GaAs layer and In 0.5 Ga 0.5 As QDs were trimethylgallium (TMGa), trimethylindium (TMIn), and arsine (AsH 3 ). The morphology and optical properties of the self-assembled In 0.5 Ga 0.5 As QDs were investigated and characterized using atomic force microscopy (AFM) and photoluminescence (PL). The AFM images revealed that the sizes of the dots on the topmost were not uniformly distributed. The average size of the dots fluctuated as the GaAs spacer layer thickness increased. A room temperature PL measurement was used to establish the quality and quantity of the stacked QDs. The PL peak position remained at 1148 nm for all samples of QDs; however, the PL intensity increased as spacer layer thickness increased. The structure of the spacer layer in the stacked QD affected the morphology of the topmost surface of the QDs. The PL measurement coherently reflected the AFM characterization, in which the strong PL spectra were caused by the uniformity and high density of the QDs. The surface morphology, structure, and optical properties of the stacked QDs are attributed to seed-layer (first layer) formation of dots and spacer layer structures.
The vertical coupling effect on the electronic states in self-assembled InAs/GaAs quantum dots
Solar Energy Materials and Solar Cells, 2006
A series of self-organized InAs/GaAs quantum dots (QDs) were grown by molecular beam epitaxy to investigate the dependence of transition energy on GaAs spacer layer thickness. The latter was varied of 60, 45, 30, 15, and 10 monolayers (MLs) for the five different samples. The photoluminescence (PL) measurements were carried out. The electronic states in coupled selfassembled InAs/GaAs QDs are investigated through PL properties with the aid of the theoretical calculation. First the energy levels of electrons and holes are calculated by solving the threedimensional Schro¨dinger equation by considering the vertical coupling effect between a finite numbers of QDs. Based on the results the energies transitions between electrons and holes levels are calculated. Modification of PL spectra by increasing number of layers was found and attributed to an increasing vertical coupling. The PL full-width at half-maximum (FWHM), reflecting the size distribution of the QDs, was found to reach a minimum for an inter-dots GaAs spacer layer thickness of 30 MLs. Moreover, the observed behavior PL lines is analyzed theoretically. r
Study of GaAs spacer layers in InAs/GaAs vertically aligned quantum dot structures
Thin Solid Films, 2000
We investigated vertically aligned InAsrGaAs QD structures, grown by atomic layer molecular beam epitaxy, with a number N of layers and with spacer thicknesses d. QD alignment and structure quality were checked by transmission electron microscopy. The dependencies of carrier capture, decay dynamics and existence of quenching channels on the design parameters N and d Ž . Ž . were studied by time resolved photoluminescence PL , PL excitation PLE and PL temperature-dependent measurements. Our results show that the carrier capture and the radiative efficiency of the QDs are negatively affected by increasing the number of QD layers and by reducing the spacer thicknesses; this effect is likely to be related to the increase of defect concentrations in GaAs spacers, due to relaxation of an increasingly large strain. ᮊ
Journal of Crystal Growth, 2005
Self-organized InAs quantum dots (QDs) are grown in the Stranski-Krastanov regime, by molecular beam epitaxy, on (1 0 0) GaAs substrates. In order to grow high-quality QDs emitting at 1.3 mm, an unusual two-step growth procedure is first developed, with a growth interruption during the InAs deposition, just above the critical thickness. Then two important growth parameters are considered. First, the GaAs cap layer deposition rate is optimized, the InAs growth being kept constant. Second, the InAs growth rate is optimized, at optimized GaAs cap layer deposition rate. The optimizations leads to large QDs with a unimodal size distribution and the room temperature photoluminescence (PL) spectrum peaks at 1.3 mm with a 19 meV full-width at half-maximum (FWHM). These optical properties are at the international state of art. Then, three QD layers are stacked with different spacer thickness in order to increase the QD density necessary for laser applications. The best optical properties are obtained for the wider GaAs spacer (45 nm): PL emission around 1.3 mm, narrow FWHM (31 meV), and PL intensity enhanced by a factor of 3. The results are promising for further incorporation of the QD stacks in the active region of a laser. r