Strong alignment of self-assembling InP quantum dots (original) (raw)
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Self-assembling InAs and InP quantum dots for optoelectronic devices
Thin Solid Films, 2000
Stranski-Krastanov growth in molecular beam epitaxy allows the preparation of self assembling InAs and InP quantum dots on GaAs and Ga0,521no,4,P buffer layers, respectively. InAs dots in GaAs prepared by slow growth rates and low temperature overgrowth provide intense photoluminescence at the technologically important wavelength of 1.3 p,m at room temperature. Strain induced vertical alignment, size modification and material interdiffusion for stacked dot layers are studied. A blue shift of the ground state transition energy is observed for the slowly deposited stacked InAs dots. This is ascribed to enhanced strain driven intermixing in vertically aligned islands. For very small densely stacked InP and InAs dots the reduced confinement shift causes a red shift of the ground state emission. The InP quantum dots show intense and narrow photoluminescence at room temperature in the visible red spectral range. First InP/Ga0,521no,4,P quantum dot injection lasers are prepared using threefold stacked InP dots. We observe lasing at room temperature in the wavelength range between 690-705 nm depending on the size of the stacked InP dots.
Journal of Electronic Materials, 2001
We report the characteristics of InP self-assembled quantum dots embedded in In 0.5 Al 0.5 P on GaAs substrates grown by metalorganic chemical vapor deposition. The InP quantum dots show increased average dot sizes and decreased dot densities, as the growth temperature increases from 475°C to 600°C with constant growth time. Above the growth temperature of 600°C, however, dramatically smaller and densely distributed self-assembled InP quantum dots are formed. The small InP quantum dots grown at 650°C are dislocation-free "coherent" regions with an average size of ~20 nm (height) and a density of ~1.5 × 10 8 mm -2 . These InP quantum dots have a broad range of luminescence corresponding to red or orange in the visible spectrum.
Nanotechnology, 2005
We report modified self-assembly of InAs islands acting as stressors for strain-induced InGaAs(P) quantum dots (SIQDs). The quantum dots are fabricated by growing InAs islands on top of a near-surface InGaAs(P)/InP quantum well (QW). The compressively strained QW affects the size and density of the InAs islands, as compared to islands grown on a plain InP buffer. By adjusting the growth conditions, the height of the InAs stressors is tuned from 15 to 30 nm while the areal density varies around 10 9 cm −2 . The confinement of carriers in the SIQDs is characterized by low-temperature photoluminescence. Increasing the size of the InAs stressor is shown to enhance the depth of the lateral confinement potential and reduce the level splitting of excited QD states. However, the small inhomogeneous broadening of the SIQD transitions, as narrow as 11 meV, shows no correlation with the height dispersion of the stressor islands.
Tensile-strained GaAsN quantum dots on InP
Applied Physics Letters, 2007
Self-assembled quantum dots are typically fabricated from compressive-strained material systems, e.g., InAs on GaAs. In this letter, self-assembled quantum dots from tensile-strained GaAsN on InP are demonstrated. GaAsN on InP has type-I band alignment. Stranski-Krastanov growth mode is not observed, but in situ annealing of the uncapped samples results in the formation of islands. Photoluminescence spectra from the buried GaAsN show separate peaks due to a wetting layer and islands around the energies of 1.3 and 1.1 eV, respectively.
Self-assembling of In(Ga)As/GaAs quantum dots on (N11) substrates: the (311)A case
Micron, 2000
We have investigated the In(Ga)As island formation, in the Stranski-Krastanov growth mode, on (311)A GaAs substrates. The surface topography of InAs and InGaAs strained epilayers was studied by contact microscopies. The different substrate affects the overgrown island shape. In(Ga)As grown on (311)A gives rise to quantum wire-like islands. Quantum dots (QDs), but with highly anisotropic shapes, are the outcomes of InAs deposition. QD samples were also characterized by photoluminescence (PL) measurements. Correlation between optical and morphological properties was observed. ᭧
The formation of InAs quantum dots by Stransky-Krastanow method on (311)B InP substrates has been studied. On Al0.48In0.52As alloy lattice matched on InP, large changes of the quantum dot structural characteristics have been observed as a function of the amount of InAs deposited and of the Arsenic pressure during the InAs quantum dot formation. Small quantum dots (minimum diameter = 20 nm) in very high density (1.3 x1011 quantum dots per cm2) have been achieved in optimized growth conditions. These results are interpreted from the strong strain field interaction through the substrate at high density and from the InAs surface energy evolutions with the Arsenic pressure. The effect on quantum dot characteristics of the arsenic pressure during the growth of Al0.48In0.52As buffer layers has been also investigated. Despite the importance of this parameter on the Al0.48In0.52As clustering, weak changes have been observed.
Physical Review B, 2008
We investigate the electronic structure of the InAs/InP quantum dots using an atomistic pseudopotential method and compare them to those of the InAs/GaAs QDs. We show that even though the InAs/InP and InAs/GaAs dots have the same dot material, their electronic structure differ significantly in certain aspects, especially for holes: (i) The hole levels have a much larger energy spacing in the InAs/InP dots than in the InAs/GaAs dots of corresponding size. (ii) Furthermore, in contrast with the InAs/GaAs dots, where the sizeable hole ppp, ddd intra-shell level splitting smashes the energy level shell structure, the InAs/InP QDs have a well defined energy level shell structure with small ppp, ddd level splitting, for holes. (iii) The fundamental exciton energies of the InAs/InP dots are calculated to be around 0.8 eV ($\sim$ 1.55 mu\mumum), about 200 meV lower than those of typical InAs/GaAs QDs, mainly due to the smaller lattice mismatch in the InAs/InP dots. (iii) The widths of the exciton PPP shell and DDD shell are much narrower in the InAs/InP dots than in the InAs/GaAs dots. (iv) The InAs/GaAs and InAs/InP dots have a reversed light polarization anisotropy along the [100] and [1$\bar{1}$0] directions.
Nanotechnology, 2012
We demonstrate a method to controllably reduce the density of self-assembled InP quantum dots (QDs) by cyclic deposition with growth interruptions. Varying the number of cycles enabled a reduction of the QD density from 7.4 × 10 10 cm −2 to 1.8 × 10 9 cm −2 for the same total amount of deposited InP. Simultaneously, a systematic increase of the QD size could be observed. Emission characteristics of different-sized InP QDs were analyzed. Excitation power dependent and time-resolved measurements confirm a transition from type I to type II band alignment for large InP quantum dots. Photon autocorrelation measurements of type I QDs performed under pulsed excitation reveal pronounced antibunching (g (2) (τ = 0) = 0.06 ± 0.03) as expected for a single-photon emitter. The described growth routine has great promise for the exploitation of InP QDs as quantum emitters.