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Dynamics of mass transport during nanohole drilling by local droplet etching.

Heyn C, Bartsch T, Sanguinetti S, Jesson D, Hansen W - Nanoscale Res Lett (2015)

Bottom Line: This paper studies the droplet material removal experimentally and discusses the results in terms of a simple model.Under consideration of these results, a simple kinetic scaling model of the etching process is proposed that quantitatively reproduces experimental data on the hole depth as a function of the process temperature and deposited amount of droplet material.Furthermore, the depth dependence of the hole side-facet angle is analyzed.

View Article: PubMed Central - PubMed

Affiliation: Institut für Angewandte Physik, Universität Hamburg, Jungiusstr. 11, Hamburg, 20355 Germany.

ABSTRACT
Local droplet etching (LDE) utilizes metal droplets during molecular beam epitaxy for the self-assembled drilling of nanoholes into III/V semiconductor surfaces. An essential process during LDE is the removal of the deposited droplet material from its initial position during post-growth annealing. This paper studies the droplet material removal experimentally and discusses the results in terms of a simple model. The first set of experiments demonstrates that the droplet material is removed by detachment of atoms and spreading over the substrate surface. Further experiments establish that droplet etching requires a small arsenic background pressure to inhibit re-attachment of the detached atoms. Surfaces processed under completely minimized As pressure show no hole formation but instead a conservation of the initial droplets. Under consideration of these results, a simple kinetic scaling model of the etching process is proposed that quantitatively reproduces experimental data on the hole depth as a function of the process temperature and deposited amount of droplet material. Furthermore, the depth dependence of the hole side-facet angle is analyzed.

No MeSH data available.


Related in: MedlinePlus

Schematic representation of the different steps of a Ga on AlGaAs droplet etching process. (a) Planar deposition of Ga with flux FGa yielding an increase of the Ga adatom density n1. Ga droplets are nucleated by collisions between diffusing Ga adatoms. (b) Droplet shape establishment with increasing coverage and increase of the droplet volume by adatom attachment with rate RA. (c) Etching and removal of substrate material by As diffusion with rate RE and droplet material detachment with rate RD during post-growth annealing. The detached Ga atoms crystallize a thin GaAs layer with background As of flux FAs. (d) Final hole with depth d and side-facet angle α surrounded by a GaAs wall.
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Fig2: Schematic representation of the different steps of a Ga on AlGaAs droplet etching process. (a) Planar deposition of Ga with flux FGa yielding an increase of the Ga adatom density n1. Ga droplets are nucleated by collisions between diffusing Ga adatoms. (b) Droplet shape establishment with increasing coverage and increase of the droplet volume by adatom attachment with rate RA. (c) Etching and removal of substrate material by As diffusion with rate RE and droplet material detachment with rate RD during post-growth annealing. The detached Ga atoms crystallize a thin GaAs layer with background As of flux FAs. (d) Final hole with depth d and side-facet angle α surrounded by a GaAs wall.

Mentions: The samples are fabricated using a solid-source MBE system equipped with a valved cracker source for As 4. A droplet-etching process takes place in two steps. First, droplet material is deposited uniformly over the substrate and droplets are formed in the Volmer-Weber growth mode driven by a minimization of the surface energy (Figures 1a, 2a,b). Here, we used a growth rate of 0.8 monolayers per second (ML/s) for Ga and 0.4 ML/s for Al. The coverage θ = 1 − 2 ML with droplet material is adjusted by the deposition time. In a subsequent post-growth thermal-annealing step of 120 to 180 s, the droplets transform into nanoholes surrounded by walls (Figures 1b, 2c,d). In the present experiments, we chose equal temperatures T for droplet deposition and annealing. The As flux is reduced to about 1 × 10−7 Torr by closing the As cell shutter and valve. During annealing, in addition, the main shutter in front of the sample is closed. In some experiments, the As background flux is further reduced as will be described below.Figure 2


Dynamics of mass transport during nanohole drilling by local droplet etching.

Heyn C, Bartsch T, Sanguinetti S, Jesson D, Hansen W - Nanoscale Res Lett (2015)

Schematic representation of the different steps of a Ga on AlGaAs droplet etching process. (a) Planar deposition of Ga with flux FGa yielding an increase of the Ga adatom density n1. Ga droplets are nucleated by collisions between diffusing Ga adatoms. (b) Droplet shape establishment with increasing coverage and increase of the droplet volume by adatom attachment with rate RA. (c) Etching and removal of substrate material by As diffusion with rate RE and droplet material detachment with rate RD during post-growth annealing. The detached Ga atoms crystallize a thin GaAs layer with background As of flux FAs. (d) Final hole with depth d and side-facet angle α surrounded by a GaAs wall.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC4385027&req=5

Fig2: Schematic representation of the different steps of a Ga on AlGaAs droplet etching process. (a) Planar deposition of Ga with flux FGa yielding an increase of the Ga adatom density n1. Ga droplets are nucleated by collisions between diffusing Ga adatoms. (b) Droplet shape establishment with increasing coverage and increase of the droplet volume by adatom attachment with rate RA. (c) Etching and removal of substrate material by As diffusion with rate RE and droplet material detachment with rate RD during post-growth annealing. The detached Ga atoms crystallize a thin GaAs layer with background As of flux FAs. (d) Final hole with depth d and side-facet angle α surrounded by a GaAs wall.
Mentions: The samples are fabricated using a solid-source MBE system equipped with a valved cracker source for As 4. A droplet-etching process takes place in two steps. First, droplet material is deposited uniformly over the substrate and droplets are formed in the Volmer-Weber growth mode driven by a minimization of the surface energy (Figures 1a, 2a,b). Here, we used a growth rate of 0.8 monolayers per second (ML/s) for Ga and 0.4 ML/s for Al. The coverage θ = 1 − 2 ML with droplet material is adjusted by the deposition time. In a subsequent post-growth thermal-annealing step of 120 to 180 s, the droplets transform into nanoholes surrounded by walls (Figures 1b, 2c,d). In the present experiments, we chose equal temperatures T for droplet deposition and annealing. The As flux is reduced to about 1 × 10−7 Torr by closing the As cell shutter and valve. During annealing, in addition, the main shutter in front of the sample is closed. In some experiments, the As background flux is further reduced as will be described below.Figure 2

Bottom Line: This paper studies the droplet material removal experimentally and discusses the results in terms of a simple model.Under consideration of these results, a simple kinetic scaling model of the etching process is proposed that quantitatively reproduces experimental data on the hole depth as a function of the process temperature and deposited amount of droplet material.Furthermore, the depth dependence of the hole side-facet angle is analyzed.

View Article: PubMed Central - PubMed

Affiliation: Institut für Angewandte Physik, Universität Hamburg, Jungiusstr. 11, Hamburg, 20355 Germany.

ABSTRACT
Local droplet etching (LDE) utilizes metal droplets during molecular beam epitaxy for the self-assembled drilling of nanoholes into III/V semiconductor surfaces. An essential process during LDE is the removal of the deposited droplet material from its initial position during post-growth annealing. This paper studies the droplet material removal experimentally and discusses the results in terms of a simple model. The first set of experiments demonstrates that the droplet material is removed by detachment of atoms and spreading over the substrate surface. Further experiments establish that droplet etching requires a small arsenic background pressure to inhibit re-attachment of the detached atoms. Surfaces processed under completely minimized As pressure show no hole formation but instead a conservation of the initial droplets. Under consideration of these results, a simple kinetic scaling model of the etching process is proposed that quantitatively reproduces experimental data on the hole depth as a function of the process temperature and deposited amount of droplet material. Furthermore, the depth dependence of the hole side-facet angle is analyzed.

No MeSH data available.


Related in: MedlinePlus