Epitaxial growth of quantum-dot heterostructures on metamorphic buffers (original) (raw)
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Formation and morphological evolution of InAs quantum dots grown by chemical beam epitaxy
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Strain Relaxation of InAs Quantum Dots on Misoriented InAlAs(111) Metamorphic Substrates
Nanomaterials
We investigate in detail the role of strain relaxation and capping overgrowth in the self-assembly of InAs quantum dots by droplet epitaxy. InAs quantum dots were realized on an In0.6Al0.4As metamorphic buffer layer grown on a GaAs(111)A misoriented substrate. The comparison between the quantum electronic calculations of the optical transitions and the emission properties of the quantum dots highlights the presence of a strong quenching of the emission from larger quantum dots. Detailed analysis of the surface morphology during the capping procedure show the presence of a critical size over which the quantum dots are plastically relaxed.
2009
Experimental characterization and theoretical study of the interband transitions of self-assembled InAs quantum dots ͑QDs͒ grown on metamorphic pseudosubstrates of In x Ga 1−x As ͑0.0ഛ x ഛ 0.3͒ are reported. The effect of the varying underlying strain on the size distribution of InAs QDs and their photoluminescence emission wavelength is investigated by employing different substrate compositions. Atomic force microscopy images of the QDs show that the ratio of the height/lateral diameter of the QDs decreases with decreasing strain and the photoluminescence of the buried InAs QDs shows that the peak wavelength redshifts with increasing In mole fraction of the underlying pseudosubstrates. A theoretical model based on the Green's function technique is used to calculate the density of states ͑DOS͒ of the QDs for the different samples based on the measured dot geometries. From the DOS, the electron and hole energy levels can be obtained, yielding the possible interband transitions. Good agreement between the model and the experimental results is obtained by allowing for Ga incorporation, from the substrate and barrier layers, into the InAs QDs and it is found that the necessary Ga mole fraction varies linearly with the Ga mole fraction in the underlying In x Ga 1−x As pseudosubstrate.
Journal of Applied Physics, 2009
Experimental characterization and theoretical study of the interband transitions of self-assembled InAs quantum dots ͑QDs͒ grown on metamorphic pseudosubstrates of In x Ga 1−x As ͑0.0ഛ x ഛ 0.3͒ are reported. The effect of the varying underlying strain on the size distribution of InAs QDs and their photoluminescence emission wavelength is investigated by employing different substrate compositions. Atomic force microscopy images of the QDs show that the ratio of the height/lateral diameter of the QDs decreases with decreasing strain and the photoluminescence of the buried InAs QDs shows that the peak wavelength redshifts with increasing In mole fraction of the underlying pseudosubstrates. A theoretical model based on the Green's function technique is used to calculate the density of states ͑DOS͒ of the QDs for the different samples based on the measured dot geometries. From the DOS, the electron and hole energy levels can be obtained, yielding the possible interband transitions. Good agreement between the model and the experimental results is obtained by allowing for Ga incorporation, from the substrate and barrier layers, into the InAs QDs and it is found that the necessary Ga mole fraction varies linearly with the Ga mole fraction in the underlying In x Ga 1−x As pseudosubstrate.
1.55 μm InAs quantum dots grown on a GaAs substrate using a GaAsSb metamorphic buffer layer
H. Y. Liu, Y. Qiu, C. Y. Jin, T. Walther, and A. G. Cullis, 2008
The use of a GaAsSb metamorphic buffer layer (MBL) is demonstrated to significantly enhance the room-temperature photoluminescence intensity for 1.55um metamorphic InAs/GaAs quantum dots (QDs) in comparison with a conventional InGaAs MBL. A dramatic reduction of QD photoluminescence emission efficiency above 1.5um has been observed at room temperature when the indium composition in the InxGa1−xAs MBL is increased over x=0.25. By using a GaAsSb buffer instead of InGaAs, we demonstrate a strong enhancement of photoluminescence intensity of InAs/GaAs QDs. The effects of the GaAsSb MBL can be understood in terms of smoothing the surface morphology of the buffer layer and, hence, suppressing the formation of dislocations in the QD region. These results suggest an alternative approach to developing GaAs-based light sources in the telecommunication-wavelength range near 1.55 um."
Applied Physics Letters, 2000
We report on the matrix-dependent strain effect in self-assembled InAs quantum-dot heterostructures using photoluminescence measurements. A series of samples were prepared to examine the effect of quantum dot position with respect to the so-called strain-reducing layer ͑SRL͒. Since the SRL reduces the residual hydrostatic strain in the quantum dots, long emission wavelength of 1.34 m is observed for the InAs quantum dots with an In 0.16 Ga 0.84 As SRL. The dependence of the emission wavelength on the thickness of the cap layer on SRL also indicates the importance of the role of matrix in the strain relaxation process of the dots. Using In 0.16 Al 0.84 As instead of In 0.16 Ga 0.84 As as the SRL, a blueshift in wavelength is observed because the elastic stiffness of In 0.16 Al 0.84 As is higher than that of In 0.16 Ga 0.84 As and less strain is removed from the dots with In 0.16 Al 0.84 As SRL.