Droplet etching of deep nanoholes for filling with self-aligned complex quantum structures

Küster, A.; Heyn, Ch.; Juška, Gediminas; Moroni, Stefano T.; Pelucchi, E.; Hansen, W.

doi:10.1186/s11671-016-1495-5

Cited by 26 publications

(17 citation statements)

References 29 publications

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“…Thus, the precise control of the droplet density is essential for the creation of quantum emitters with well-defined properties. For instance, low density QDs [ 25 ] are relevant as single-photon sources for quantum information technology and high density dots [ 26 ] for device applications such as lasers or solar cells. The central process parameter controlling the droplet density is the substrate temperature T .…”

Section: Introductionmentioning

confidence: 99%

Modeling of Al and Ga Droplet Nucleation during Droplet Epitaxy or Droplet Etching

Heyn

Feddersen

2021

Nanomaterials

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The temperature dependent density of Al and Ga droplets deposited on AlGaAs with molecular beam epitaxy is studied theoretically. Such droplets are important for applications in quantum information technology and can be functionalized e.g., by droplet epitaxy or droplet etching for the self-assembled generation of quantum emitters. After an estimation based on a scaling analysis, the droplet densities are simulated using first a mean-field rate model and second a kinetic Monte Carlo (KMC) simulation basing on an atomistic representation of the mobile adatoms. The modeling of droplet nucleation with a very high surface activity of the adatoms and ultra-low droplet densities down to 5 × 106 cm−2 is highly demanding in particular for the KMC simulation. Both models consider two material related model parameters, the energy barrier ES for surface diffusion of free adatoms and the energy barrier EE for escape of atoms from droplets. The rate model quantitatively reproduces the droplet densities with ES = 0.19 eV, EE = 1.71 eV for Al droplets and ES = 0.115 eV for Ga droplets. For Ga, the values of EE are temperature dependent indicating the relevance of additional processes. Interestingly, the critical nucleus size depends on deposition time, which conflicts with the assumptions of the scaling model. Using a multiscale KMC algorithm to substantially shorten the computation times, Al droplets up to 460 ℃ on a 7500 × 7500 simulation field and Ga droplets up to 550 ℃ are simulated. The results show a very good agreement with the experiments using ES = 0.19 eV, EE = 1.44 eV for Al, and ES = 0.115 eV, EE = 1.24 eV (T≤ 300 ℃) or EE = 1.24 + 0.06 (T[℃]-300)/100 eV (T>300 ℃) for Ga. The deviating EE is attributed to a re-nucleation effect that is not considered in the mean-field assumption of the rate model.

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Section: Introductionmentioning

confidence: 99%

Modeling of Al and Ga Droplet Nucleation during Droplet Epitaxy or Droplet Etching

Heyn

Feddersen

2021

Nanomaterials

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“…This technique, local droplet etching (LDE), allows for the creation of unstrained, pure and highly uniform QDs [ 19 ]. LDE QDs have been widely studied at helium temperatures and shown to have state-of-the-art optical properties, with exciton-peak line width down to 25

eV [ 19 , 25 , 26 ], neutral exciton fine-structure splitting as low as

eV [ 26 ] and single photon emission proven by a second-order correlation function of 0.01 [ 27 ].…”

Section: Introductionmentioning

confidence: 99%

Luminescence from Droplet-Etched GaAs Quantum Dots at and Close to Room Temperature

et al. 2021

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Epitaxially grown quantum dots (QDs) are established as quantum emitters for quantum information technology, but their operation under ambient conditions remains a challenge. Therefore, we study photoluminescence (PL) emission at and close to room temperature from self-assembled strain-free GaAs quantum dots (QDs) in refilled AlGaAs nanoholes on (001)GaAs substrate. Two major obstacles for room temperature operation are observed. The first is a strong radiative background from the GaAs substrate and the second a significant loss of intensity by more than four orders of magnitude between liquid helium and room temperature. We discuss results obtained on three different sample designs and two excitation wavelengths. The PL measurements are performed at room temperature and at T = 200 K, which is obtained using an inexpensive thermoelectric cooler. An optimized sample with an AlGaAs barrier layer thicker than the penetration depth of the exciting green laser light (532 nm) demonstrates clear QD peaks already at room temperature. Samples with thin AlGaAs layers show room temperature emission from the QDs when a blue laser (405 nm) with a reduced optical penetration depth is used for excitation. A model and a fit to the experimental behavior identify dissociation of excitons in the barrier below T = 100 K and thermal escape of excitons from QDs above T = 160 K as the central processes causing PL-intensity loss.

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“…An alternative fabrication method comprises the local droplet etching (LDE) of semiconductor surfaces [21][22][23][24][25], by which self-assembled nanoholes are formed. Filling of nanoholes in AlGaAs allows for the creation of strain-free GaAs QDs [26,27]. Aside from single QDs, also vertically stacked quantum dot molecules with strong coupling [28] and ultrashort nanopillars [29] for thermoelectric applications are fabricated by filling of LDE nanoholes.…”

Section: Introductionmentioning

confidence: 99%

Faceting of local droplet-etched nanoholes in AlGaAs

Vonk

Slobodskyy

Keller

et al. 2018

Phys. Rev. Materials

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Nanoholes, drilled in the (001) surface of AlGaAs by local Al droplet etching, are shown to consist of faceted inner walls. The most prominent facets of the inverted pyramidlike nano-sized etch pits are the {111}A and {111}B surfaces, which differ in their atomic surface terminations. In the [110] direction, the {111} facets change to {112} and/or {113}, which are both stepped surfaces with (111)A terraces. Etching-temperaturedependent data indicate that this facet transition seems kinetically hindered up to etch temperatures above 660°C, at which point the walls along [110] have already evolved completely towards {111}B facets. The redeposited ring material outside the nanohole develops facets with indices of (115) and higher, thereby forming relatively flat structures. The facets and their indices are unraveled by a combination of atomic force microscopy, scanning electron microscopy, and x-ray diffraction, which is performed on an ensemble as well as on a single hole using nanodiffraction. These results imply that this nanoconfined etching process can be largely understood in a vapor-liquid-solid scheme, which includes the bulk thermodynamics in the AlGa As system, the surface energies of low index facets, and their etch rates and surface terminations.

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Droplet etching of deep nanoholes for filling with self-aligned complex quantum structures

Cited by 26 publications

References 29 publications

Modeling of Al and Ga Droplet Nucleation during Droplet Epitaxy or Droplet Etching

Modeling of Al and Ga Droplet Nucleation during Droplet Epitaxy or Droplet Etching

Luminescence from Droplet-Etched GaAs Quantum Dots at and Close to Room Temperature

Faceting of local droplet-etched nanoholes in AlGaAs

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