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An STM-based study of Bi deposition on InAs(110)

Alpskog, Tobias LU (2020) FYSK02 20192
Synchrotron Radiation Research
Department of Physics
Abstract
III-V semiconductor compounds containing Bi, such as InBi, have recently attracted much attention due to predictions of band inversion and topological insulators. The predictions showed that films of InBi could be applicable in quantum computers and at room temperature. The common approach of realizing such a structure, by growing InAsBi films, has not been successful, as the Bi content has been far too low for the properties of interest to emerge.

The work presented in this thesis explores an alternative approach to forming the InBi films – with a clean InAs(110) sample as a starting point. Bi is deposited onto the sample via thermal evaporation, keeping the sample at room temperature. If successful, the Bi atoms are believed to... (More)
III-V semiconductor compounds containing Bi, such as InBi, have recently attracted much attention due to predictions of band inversion and topological insulators. The predictions showed that films of InBi could be applicable in quantum computers and at room temperature. The common approach of realizing such a structure, by growing InAsBi films, has not been successful, as the Bi content has been far too low for the properties of interest to emerge.

The work presented in this thesis explores an alternative approach to forming the InBi films – with a clean InAs(110) sample as a starting point. Bi is deposited onto the sample via thermal evaporation, keeping the sample at room temperature. If successful, the Bi atoms are believed to undergo an exchange process where they replace the exposed As atoms in the lattice. This would, in turn, enable us to facilitate a higher and more homogeneous Bi incorporation as well as providing an atomically sharp interface between the top layer and the rest of the substrate. The main goal was, therefore, to determine whether the Bi atoms would be incorporated into the host lattice via the Bi-for-As exchange process, or if they would be desorbed and leave the surface. The idea of the exchange process is supported by the previous work on Sb deposition on GaAs and InAs nanowires.

The InAs(110) sample, and the effect of the Bi deposition approach, was studied by scanning tunneling microscopy (STM). By studying the STM images taken, it became evident that the deposited Bi atoms formed monolayer high islands that had a larger rectangular structure than the underlying substrate. Furthermore, the unit cell of the Bi structure was rotated 35.4° clockwise relative to the InAs(110) unit cell. The different structure, as compared to the substrate, indicated that the islands were metallic Bi.

After the Bi deposition, the InAs(110) sample was annealed. However, with only STM to study the sample, it was difficult to tell whether most of the Bi atoms were desorbed from the surface, exposing a much rougher InAs(110) surface, or, if the Bi had been incorporated either as InBi or InAs_(x)Bi_(1−x). (Less)
Popular Abstract (Swedish)
Under andra hälften av 1900-talet applicerades kunskapen av halvledare i form av bland annat transistorer, komponenter i radioapparater, och LED-lampor. Sedan dess har halvledare blivit desto mindre och desto kraftfullare. Persondatorn Apple II, som introducerades 1977 av Steve Wozniak och Steve Jobs, innehöll en processor med cirka 3000 transistorer. Idag rymmer de flesta speldatorer grafikkort som innehåller 7.2 miljarder transistorer. Framtidens datorer, kvantdatorer, kommer att rymma en oerhörd beräkningskraft. Idag existerar ett antal konkurrerande koncept angående hur man bygger en kvantdator. En av dem är att använda sig av halvledarmaterial, vars fördel är skalbarhet. För att förverkliga konceptet krävs emellertid en ökad... (More)
Under andra hälften av 1900-talet applicerades kunskapen av halvledare i form av bland annat transistorer, komponenter i radioapparater, och LED-lampor. Sedan dess har halvledare blivit desto mindre och desto kraftfullare. Persondatorn Apple II, som introducerades 1977 av Steve Wozniak och Steve Jobs, innehöll en processor med cirka 3000 transistorer. Idag rymmer de flesta speldatorer grafikkort som innehåller 7.2 miljarder transistorer. Framtidens datorer, kvantdatorer, kommer att rymma en oerhörd beräkningskraft. Idag existerar ett antal konkurrerande koncept angående hur man bygger en kvantdator. En av dem är att använda sig av halvledarmaterial, vars fördel är skalbarhet. För att förverkliga konceptet krävs emellertid en ökad förståelse av halvledarmaterial med egenskaper som är särskilt användbara inom kvantberäkning.

Det överväldigande antalet halvledarkomponenter i relativt små elektronikenheter möjliggörs av halvledarkomponenternas storlek. De befinner sig på nanometer-skalan och kan därför inte längre ses med hjälp av ett ljusmikroskop. På den här skalan dominerar kvantmekanikens lagar, vilket gör forskning om nya halvledarmaterial särskilt utmanande. Speciella tekniker, som till exempel sveptunnelmikroskopi (STM), måste användas för att kunna studera halvledarmaterialen i detalj. Med STM är det möjligt att utskilja enstaka atomer på ytan av ett halvledarmaterial. Tekniken är därför särskilt lämplig metod att använda för att detaljerat studera ytans struktur.

I det här arbetet har jag använt mig av STM för att studera halvledarmaterialet indiumarsenid (InAs) och hur dess yta påverkas av vismut-deposition (Bi-deposition). Vismut (Bi), i fast tillstånd, uppvärmdes tills det övergick till flytande tillstånd och till sist förångades. Ångan riktades mot provet av InAs med målet att erhålla mindre än ett monolager Bi på dess yta. Studien lade fokus på hur Bi-atomerna band sig till InAs-ytan: om de gjorde det via en utväxlingsprocess där Bi-atomerna ersatte As-atomerna för att skapa ett tunt lager InBi, som förutspåtts vara ett lovande halvledarmaterial vars applikationer inkluderar kvantberäkning, eller om de istället band sig svagt som adsorberade atomer.

STM-bilderna visade mindre än ett monolager av Bi-atomer. Bilderna innehöll också öar, vars struktur skiljde sig från strukturen av den underliggande ytan. Den nya strukturen tros därför vara relaterad till Bi-atomerna. En föreslagen orientering och storlek på det minsta upprepade mönstret av den Bi-relaterade ytstrukturen presenteras i arbetet. Dessutom diskuteras en förändring av den Bi-relaterade ytstrukturen som konsekvens av uppvärmning av provet. Det krävs emellertid komplementerande mätningar för att urskilja det kemiska tillståndet av ytans Bi-atomer. (Less)
Please use this url to cite or link to this publication:
author
Alpskog, Tobias LU
supervisor
organization
course
FYSK02 20192
year
type
M2 - Bachelor Degree
subject
keywords
Bismuth, Deposition, STM
language
English
id
9005742
date added to LUP
2020-03-13 13:56:09
date last changed
2020-03-13 13:56:09
@misc{9005742,
  abstract     = {{III-V semiconductor compounds containing Bi, such as InBi, have recently attracted much attention due to predictions of band inversion and topological insulators. The predictions showed that films of InBi could be applicable in quantum computers and at room temperature. The common approach of realizing such a structure, by growing InAsBi films, has not been successful, as the Bi content has been far too low for the properties of interest to emerge.

The work presented in this thesis explores an alternative approach to forming the InBi films – with a clean InAs(110) sample as a starting point. Bi is deposited onto the sample via thermal evaporation, keeping the sample at room temperature. If successful, the Bi atoms are believed to undergo an exchange process where they replace the exposed As atoms in the lattice. This would, in turn, enable us to facilitate a higher and more homogeneous Bi incorporation as well as providing an atomically sharp interface between the top layer and the rest of the substrate. The main goal was, therefore, to determine whether the Bi atoms would be incorporated into the host lattice via the Bi-for-As exchange process, or if they would be desorbed and leave the surface. The idea of the exchange process is supported by the previous work on Sb deposition on GaAs and InAs nanowires.

The InAs(110) sample, and the effect of the Bi deposition approach, was studied by scanning tunneling microscopy (STM). By studying the STM images taken, it became evident that the deposited Bi atoms formed monolayer high islands that had a larger rectangular structure than the underlying substrate. Furthermore, the unit cell of the Bi structure was rotated 35.4° clockwise relative to the InAs(110) unit cell. The different structure, as compared to the substrate, indicated that the islands were metallic Bi.

After the Bi deposition, the InAs(110) sample was annealed. However, with only STM to study the sample, it was difficult to tell whether most of the Bi atoms were desorbed from the surface, exposing a much rougher InAs(110) surface, or, if the Bi had been incorporated either as InBi or InAs_(x)Bi_(1−x).}},
  author       = {{Alpskog, Tobias}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{An STM-based study of Bi deposition on InAs(110)}},
  year         = {{2020}},
}