arXiv subjects

Vladimir G. Dubrovskii

Publications and source records attributed to Vladimir G. Dubrovskii.

5 recordsLinked to original sources

arXiv2021

Droplet epitaxy symmetric InAs/InP quantum dots for quantum emission in the third telecom window: morphology, optical and electronic properties

The rapidly developing quantum communication technology requires deterministic quantum emitters that can generate single photons and entangled photon pairs in the third telecom window, in order to be compatible with existing optical fiber networks and on-chip silicon photonic processors. InAs/InP quantum dots (QDs) are among the leading candidates for this purpose, due to their high emission efficiency in the required spectral range. However, fabricating versatile InAs/InP QD-based quantum emitters is challenging, especially as these QDs typically have asymmetric profiles in the growth plane, resulting in a substantial bright-exciton fine structure splitting (FSS). This hinders the generation of entangled photon pairs and thus, compromises the versatility of InAs/InP QDs. We overcome this by implementing droplet epitaxy (DE) synthesis of low surface density (2.8$\times$10$^8$ cm$^{-2}$) InAs QDs on an (001)-oriented InP substrate. The resulting QDs are located in etched pits, have concave bases, and most importantly, have symmetric in-plane profiles. We provide an analytical model to explain the kinetics of pit formation and QD base shape modification. Our theoretical calculations of electronic states reveal the properties of neutral and charged excitons and biexcitons confined in such QDs, which agree with the optical investigations of individual QDs. The optical response of QD ensembles suggests that FSS may indeed be negligible, as reflected in the vanishing degree of linear polarization. However, single QD spectrum gathered from an etched mesa shows moderate FSS of (50$\pm$5) $μ$eV that we link to destructive changes made in the QD environment during the post-growth processing. Finally, we show that the studied DE QDs provide a close-to-ideal single-photon emission purity of (92.5$\pm$7.5) $\%$ in the third telecom window.

cond-mat.mes-hall↗

arXiv2019

Analysis of incubation time preceding the Ga-assisted nucleation and growth of GaAs nanowires on Si(111)

The incubation time preceding nucleation and growth of surface nanostructures is interesting from a fundamental viewpoint but also of practical relevance as it determines statistical properties of nanostructure ensembles such as size homogeneity. Using in situ reflection high-energy electron diffraction, we accurately deduce the incubation times for Ga-assisted GaAs nanowires grown on unpatterned Si(111) substrates by molecular beam epitaxy under different conditions. We develop a nucleation model that explains and fits very well the data. We find that, for a given temperature and Ga flux, the incubation time always increases with decreasing As flux and becomes infinite at a certain minimum flux, which is larger for higher temperature. For given As and Ga fluxes, the incubation time always increases with temperature and rapidly tends to infinity above 640 °C under typical conditions. The strong temperature dependence of the incubation time is reflected in a similar variation of the nanowire number density with temperature. Our analysis provides understanding and guidance for choosing appropriate growth conditions that avoid unnecessary material consumption, long nucleation delays, and highly inhomogeneous ensembles of nanowires. On a more general ground, the existence of a minimum flux and maximum temperature for growing surface nanostructures should be a general phenomenon pertaining for a wide range of material-substrate combinations.

cond-mat.mtrl-sci↗

arXiv2018

Template-assisted scalable nanowire networks

Topological qubits based on Majorana fermions have the potential to revolutionize the emerging field of quantum computing by making information processing significantly more robust to decoherence. Nanowires (NWs) are a promising medium for hosting these kinds of qubits, though branched NWs are needed to perform qubit manipulations. Here we report gold-free templated growth of III-V NWs by molecular beam epitaxy using an approach that enables patternable and highly regular branched NW arrays on a far greater scale than what has been reported thus far. Our approach relies on the lattice-mismatched growth of InAs on top of defect-free GaAs nanomembranes (NMs) yielding laterally-oriented, low-defect InAs and InGaAs NWs whose shapes are determined by surface and strain energy minimization. By controlling NM width and growth time, we demonstrate the formation of compositionally graded NWs with cross-sections less than 50 nm. Scaling the NWs below 20 nm leads to the formation of homogenous InGaAs NWs which exhibit phase-coherent, quasi-1D quantum transport as shown by magnetoconductance measurements. These results are an important advance towards scalable topological quantum computing.

quant-ph↗

arXiv2016

Molecular beam epitaxy of InAs nanowires in SiO2 nanotube templates: challenges and prospects for integration of III-Vs on Si

Guided growth of semiconductor nanowires in nanotube templates has been considered as a potential platform for reproducible integration of III-Vs on silicon or other mismatched substrates. Herein, we report on the challenges and prospects of molecular beam epitaxy of InAs nanowires on SiO2/Si nanotube templates. We show how and under which conditions the nanowire growth is initiated by In-assisted vapor-liquid-solid growth enabled by the local conditions inside the nanotube template. The conditions for high yield of vertical nanowires are investigated in terms of the nanotube depth, diameter and V/III flux ratios. We present a model that further substantiates our findings. This work opens new perspectives for monolithic integration of III-Vs on the silicon platform enabling new applications in the electronics, optoelectronics and energy harvesting arena.

cond-mat.mtrl-sci↗

arXiv2013

Nanoscale resolution scanning thermal microscopy with thermally conductive nanowire probes

Scanning thermal microscopy (SThM) - a type of scanning probe microscopy that allows mapping thermal transport and temperatures in nanoscale devices, is becoming a key approach that may help to resolve heat dissipation problems in modern processors and develop new thermoelectric materials. Unfortunately, performance of current SThM implementations in measurement of high thermal conductivity materials continues to me limited. The reason for these limitations is two-fold - first, SThM measurements of high thermal conductivity materials need adequate high thermal conductivity of the probe apex, and secondly, the quality of thermal contact between the probe and the sample becomes strongly affected by the nanoscale surface corrugations of the studied sample. In this paper we develop analytical models of the SThM approach that can tackle these complex problems - by exploring high thermal conductivity nanowires as a tip apex, and exploring contact resistance between the SThM probe and studied surface, the latter becoming particularly important when both tip and surface have high thermal conductivities. We develop analytical model supported by the finite element analysis simulations and by the experimental tests of SThM prototype using carbon nanotube (CNT) at the tip apex as a heat conducting nanowire. These results elucidate vital relationships between the performance of the probe in SThM from one side and thermal conductivity, geometry of the probe and its components from the other, providing pathway for overcoming current limitations of SThM.

cond-mat.mes-hall↗