InAs heteroepitaxy on nanopillar-patterned GaAs (111)A

Physical Review Materials, 2020

We analyze the shape and position of heteroepitaxial InAs islands on the top face of cylindrical GaAs(111)A nanopillars experimentally and theoretically. Catalyst-free molecular beam epitaxial growth of InAs at low temperatures on GaAs nanopillars results in InAs islands with diameters < 30 nm exhibiting predominantly rounded triangular in-plane shapes. The islands show a tendency to grow at positions displaced from the center towards the pillar edge. Atomistic molecular statics simulations evidence that triangular-prismatic islands centered to the pillar axis with diameters smaller than that of the nanopillars are energetically favored. Moreover, we reveal the existence of minimum-energy states for off-axis island positions, in agreement with the experiment. These findings are interpreted by evaluating the spatial strain distributions and the number of broken bonds of surface atoms as a measure for the surface energy. The preferred off-axis island positions can be understood in terms of an increased compliancy of the GaAs nanopillar beneath the island because of the vicinity of free surfaces, leading to a reduction of strain energy. The influence of surface steps on the energy of the system is addressed as well.

Applied Physics Letters, 2004

We describe the growth and characterization of InAs quantum dots (QDs) on a patterned GaAs substrate using metalorganic chemical vapor deposition. The QDs nucleate on the ͑001͒ plane atop GaAs truncated pyramids formed by a thin patterned SiO 2 mask. The base diameter of the resulting QDs varies from 30 to 40 nm depending on the size of the mask. With specific growth conditions, we are able to form highly crystalline surface QDs that emit at 1.6 m under room-temperature photopumped conditions. The crystalline uniformity and residual strain is quantified in high-resolution transmission electron microscopy images and high-resolution x-ray reciprocal space mapping. These strained QDs may serve as a template for selective nucleation of a stacked QD active region.

Applied Surface Science, 2008

Formation of self-assembled InAs 3D islands on GaAs (1 1 0) substrate by metal organic vapor phase epitaxy has been investigated. Relatively uniform InAs islands with an average areal density of 10 9 cm À2 are formed at 400 C using a thin InGaAs strain reducing (SR) layer. No island formation is observed without the SR layer. Island growth on GaAs (1 1 0) is found to require a significantly lower growth temperature compared to the more conventional growth on GaAs (1 0 0) substrates. In addition, the island height is observed to depend only weakly on the growth temperature and to be almost independent of the V/III ratio and growth rate. Low-temperature photoluminescence at 1.22 eV is obtained from the overgrown islands. #

Journal of Crystal Growth, 1996

Strained, coherent InAs islands were grown in the Stranski-Krastanov growth mode on patterned GaAs by chemical beam epitaxy. The present work represents initial steps in quantitatively understanding the placement and growth of islands in patterns. The trade-offs between regular pattern features and better island nucleation are demonstrated by a deposition on a pattern of concentric circles. InAs mass transport is also measured, where material is seen to move on the order of a micron to and from different local orientations. An important practical result is that the pattern definition for island alignment need not be finer than 0.25 I~m, within the reach of present-day optical lithography.

Japanese Journal of Applied Physics, 2003

In order to fabricate uniform InAs quantum dots on a GaAs(001) substrate, the shape transition from two-dimensional (2D) to 3D islands was investigated in the case of molecular beam epitaxy via the Stranski-Krastanov growth mode. A critical lateral size of the 2D islands, just before the 3D formation, depended on the growth conditions. In case of high growth rate and high arsenic pressure conditions, the critical size became small because of the multi nucleation mode. The stacked 2D islands induced a large fluctuation in the critical lateral size and caused large inhomogeneous broadening in the pyramidal 3D dots, which were covered by the stable facets. Therefore, the low growth rate and the low arsenic pressure were effective conditions to achieve uniform 2D and 3D islands.

Journal of Crystal Growth, 2009

The molecular beam epitaxy (MBE) growth of GaAs and InAs quantum dots on etched mesas has been studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The [0 11]oriented mesas are etched into (1 0 0) GaAs substrates, exposing (5 3 3)B sidewall facets. At a substrate temperature of 610 1C a top (1 0 0) plane is seen to evolve on a ridge mesa structure. Alternatively, if the overgrowth is carried out at 630 1C no such facet is seen, and the top ridge remains unchanged during GaAs growth. By controlling the mesa shape, either ordered lines of dots can be grown or the dot density can be varied from o5 Â 10 8 cm À2 to 41 Â10 11 cm À2 on the same substrate in pre-defined regions. The dot distribution observed on the mesa sidewalls and top is discussed in terms of net migration of adatoms from different facets, underlying step density, step height and surface curvature of the mesa top.

Semiconductor Science and Technology, 2002

Applied Physics Letters, 2003

Substantial defect reduction was achieved in InAs/GaAs by lateral epitaxial overgrowth in which InAs was grown on mask-patterned ͑100͒ GaAs with stripe-shaped windows of various widths by metalorganic chemical vapor deposition. The InAs growth morphology, crystal quality, and microstructure were evaluated using double-crystal x-ray rocking curves and scanning and transmission electron microscopy. The microstructure of the InAs grown on mask-free control samples was comprised of micron-scale misoriented grains and dislocations at a density of 10 11 cm Ϫ2. As the width of the mask openings decreased to 0.8 m, the rocking curves narrowed, grain boundaries disappeared and the dislocation density decreased to Ͻ10 7 cm Ϫ2. The distribution of the remaining defects suggests substantial changes in microstructural development when the window width is Շ1 m.

Physica E: Low-dimensional Systems and Nanostructures, 2009

Thin InAs epilayers were grown on GaAs(1 0 0) substrates exactly oriented and misoriented toward [111]A direction by atmospheric pressure metalorganic vapor phase epitaxy. InAs growth was monitored by in situ spectral reflectivity. Structural quality of InAs layers were studied by using highresolution X-ray diffraction. No crystallographic tilting of the layers with respect to any kind of these substrates was found for all thicknesses. This result is discussed in terms of In-rich growth environment. InAs layers grown on 21 misoriented substrate provide an improved crystalline quality. Surface roughness of InAs layers depend on layer thickness and substrate misorientation.

Journal of Applied Physics, 2013

We present an experimental and theoretical analysis of the influence of a surface nanopattern on the properties of embedded InAs/GaAs quantum dots (QD). In particular, we analyze QDs grown on nanoimprint lithography (NIL) patterned grooves and investigate the influence of the non-planar surface morphology on the size, shape, strain distribution, and electronic structure of the embedded QDs. We show that the height reduction of InAs QDs during GaAs capping is significantly less pronounced for the QDs grown on the pattern than for the self-assembled QDs. Furthermore, the pattern has a strong impact on the strain and composition profile within the QD. The experimentally observed strain distribution was successfully reproduced with a three-dimensional model assuming an inverse-cone type composition gradient. Moreover, we show that the specific morphology of the QDs grown in the grooves gives rise to an increase of the vertically polarized photoluminescence emission which was explained by employing 8-band k.p calculations. Our findings emphasize that the surface curvature of the pattern not only determines the nucleation sites of the QDs but also has a strong impact on their morphological properties including shape, size, composition profile, and strain distribution. These properties are strongly cross-correlated and determine the electronic and optical characteristics of the QDs. V C 2013 AIP Publishing LLC.