Leveling and rebuilding: An approach to improve the uniformity of (In,Ga)As quantum dots

Abstract

We report on an approach to improve the uniformity of a single layer of (In,Ga)As quantum dots (QDs) grown by molecular-beam epitaxy. The key concept of our approach is to level and rebuild the (In,Ga)As QDs during insertion of a short period GaAs/InAs superlattice between the (In,Ga)As QD layer and the GaAs capping layer. For optimized layer thickness and number of superlattice periods this process results in uniform (In,Ga)As QDs with narrow photoluminescence line width of 20 meV at 4.5 K.

Formation of columnar (In,Ga)As quantum dots on GaAs(100)

“…During deposition of the GaAs intermediate layer and following growth interruption, the chevrons evolve into short, streaky diffraction rods, due to leveling of the QDs. 9,12 When the subsequent InAs layer is grown, the RHEED pattern changes back and during growth interruption clear chevrons develop, which indicate rebuilding of InAs QDs. The critical thickness for InAs QD rebuilding is 0.9 ML, which is much smaller than that of 1.7 ML for formation of the seed QDs.…”

“…[4][5][6][7][8] We have recently introduced leveling and rebuilding of InAs QDs on GaAs͑100͒ substrates during molecular beam epitaxy (MBE) of multiple ultrathin GaAs/ InAs overlayers which drastically improves the QD size uniformity and optical properties due to the exchange of InAs between neighboring QDs. 9 Here we report leveling and rebuilding as an effective route for the creation of height controlled columnar ͑In,Ga͒As QDs. The introduction of extended growth interruptions after alternating deposition of the thin GaAs and InAs layers on InAs seed QDs produces columnar ͑In,Ga͒As QDs which are uniform both in composition and shape in the growth direction, and whose height is directly determined by the number of stacked GaAs/ InAs layers.…”

InAs Quantum Dot Formation Studied at the Atomic Scale by Cross-sectional Scanning Tunnelling Microscopy

“…Levelling of InAs/GaAs QDs after deposition of thin GaAs cap layers has been clearly revealed by top-view STM [18,58] and atomic force microscopy (AFM) [54]. The levelling process has been attributed to the additional strain build-up between the cap layer and the partially relaxed InAs QDs [18,54] to destabilize the QDs.…”

“…The growth rates were 0.58 and 0.06ML/s for GaAs and InAs, respectively, and the As A beam equivalent pressure was 1 X 10~5torr. It is well established that InAs QDs buried in the conventional way of sample A exhibit a reduced height compared to unburied ones due to QD levelling [18,53,54]. In order to determine the QD height reduction, the shape change during overgrowth of the InAs QDs in sample B is strongly suppressed by capping them at 300°C.…”

“…The levelling process has been attributed to the additional strain build-up between the cap layer and the partially relaxed InAs QDs [18,54] to destabilize the QDs. These experiments, however, lack information about the shape and, in particular, the residual height of the QDs which is the most important parameter determining the electronic properties.…”