Self-organization processes of InGaAs/GaAs quantum dots grown by metalorganic chemical vapor deposition

Abstract

In 0.5 Ga 0.5 As/GaAs ͑001͒ quantum dots ͑QDs͒ were grown by metalorganic chemical vapor deposition ͑MOCVD͒ on exactly ͑001͒ oriented substrates using the Stranski-Krastanow growth mode. The dot density and their relative geometrical arrangement are found to be strongly dependent on the substrate temperature. The dots have identical square shaped bases oriented along ͗100͘. For high densities a preferential relative alignment of the dots along the ͗110͘ directions is found. These dots tend to be arranged in a chainlike pattern with decreasing dot size towards the ends of the chains. From these observations the dot formation process for In 0.5 Ga 0.5 As quantum dots is suggested to be driven by energetics whereas the relative orientation is governed by kinetic effects. © 1996 American Institute of Physics.͓S0003-6951͑96͒00923-0͔Heteroepitaxial growth of highly strained structures like In x Ga 1Ϫx As/GaAs has gained increasing interest as it offers the possibility to fabricate self-organized structures like quantum dots ͑QDs͒ and quantum wires without any substrate patterning process. These low dimensional structures show unique physical properties, particularly interesting for novel optoelectronic devices like QD lasers with low threshold current density and high T 0 . 1 A fundamental question for future applications is whether dot formation is kinetically driven or due to minimization of total energy. The latter leads to sharper dot size and shape distributions. Thermodynamical equilibrium calculations predict a hierarchical series of self-organization processes. 2 According to these calculations the equilibrium state for a dilute quantum dot array is an ensemble of identically shaped pyramids of square base parallel ͗100͘. Their equilibrium size is defined by the ratio of facet energy and strain relation at facet edges. For a dense array the interaction between the individual dots via strain fields leads to an alignment of the dots on a two-dimensional square array oriented along the ͗100͘ directions thus representing an even higher level of self-organization.For QD structures grown by molecular beam epitaxy ͑MBE͒ there exists a wealth of information 3-7 including the first observation of self-organization of InAs quantum dots. 7 For MBE grown In x Ga 1Ϫx As dots ͑0.3ϽxϽ0.6͒ on singular ͑001͒ surfaces the formation of wirelike structure oriented along ͗110͘ has been observed. 8,9 In contrast there exist only very few reports on metalorganic chemical vapor deposition ͑MOCVD͒ grown InGaAs/GaAs QDs. 10,11 Preferential dot formation at surface steps has been observed for grown on misoriented substrates. 10 Self-ordering of dots grown by MOCVD on exactly oriented substrates has not yet been reported. In this letter, we present the first observation of selforganization of InGaAs/GaAs quantum dot structures grown by MOCVD on exactly oriented substrates. We find the dots to be aligned along the ͗110͘ directions in contrast to the alignment found for MBE grown InAs dots, though their base shape is identical to MBE grown ...

Semiconductor nanostructures for flying q-bits and green photonics

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Dephasing in InAs/GaAs quantum dots

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Design and Realization of Novel GaAs Based Laser Concepts

“…Thus, the real wafer surface temperature for a full 2" wafer is increased compared to a quarter wafer for the same set process temperature. This is an important finding for all highly optimized nanostructure growth processes as QD formation are particularly well known to be highly temperature sensitive [Hei96]. The influence of wafer size change on optical properties of a highly optimized five-fold 1.3 µm QD stack is shown in Figure 5.…”