Question about Quantum dot (picture)


by McCloud
Tags: picture, quantum
McCloud
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#1
May22-11, 12:12 AM
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Hi all!! Can anyone tell me What this picture of a quantum dot means?? The signifigance of what this exact picture stands for. What does it prove??
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f95toli
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May22-11, 10:34 AM
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It is a scanning electron microscope (SEM) picture of a what looks like a double quantum dot (two QDs next to each other).

The pale lines (labelled V1, V2 etc) are gate lines used to apply the voltage potential that defines the dots in the centre. The gate lines are metallic and are fabricated on top of a III-V semiconductor (such as GaAs) that has been made in such a way that there is a quasi-2D electron gas (known as a 2DEG) some distance under the surface, by applyting the gate voltage the electrons are confined in the XY plane which in turn creates a dot (or in this case 2.
I like Serena
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May22-11, 10:47 AM
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Quote Quote by f95toli View Post
It is a scanning electron microscope (SEM) picture of a what looks like a double quantum dot (two QDs next to each other).

The pale lines (labelled V1, V2 etc) are gate lines used to apply the voltage potential that defines the dots in the centre. The gate lines are metallic and are fabricated on top of a III-V semiconductor (such as GaAs) that has been made in such a way that there is a quasi-2D electron gas (known as a 2DEG) some distance under the surface, by applyting the gate voltage the electrons are confined in the XY plane which in turn creates a dot (or in this case 2.
Wow!

I thought I knew a little about physics, but this totally passed over my head!

I am interested though in some basic understanding....

What does it do?
What's the point of using GaAs or whatever?
What's a III-V semiconductor?
How does it generate an electron gas?
What is a quasi-2D electron gas anyway?
Why would the electrons be confined to the XY plane?
How is it that a dot is created because of this?

And before you refer me to the wikipedia article, I've already read it.
I did learn something from it, but there's a lot there too that I don't quite understand.

f95toli
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May22-11, 12:34 PM
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Question about Quantum dot (picture)


Quote Quote by I like Serena View Post
What does it do?
They are used in various applications (detectors etc). It is basically as close to a 1D quantum well you can get. I think I read somewhere that Samsung is even working on flatscreen TVs based on QDs.


What's the point of using GaAs or whatever?
GaAs is the second most common semiconducting material (the most common being silicon). It is a very controllable material and can -when combined with various amount of aluminium- be used to make controlled potentiall wells. Most laser diods etc are made from GaAs and so are virtually all high-frequency transistors (e.g. HEMTs used in mobile phones etc).



What's a III-V semiconductor?
A semiconducting material made form one element from group III and one from group V in the periodic table. GaAs, GaN, InAs,InP etc


How does it generate an electron gas?
What is a quasi-2D electron gas anyway?
Why would the electrons be confined to the XY plane?
The gas forms at an interface where there are no free states that the elctrons can move into above or below. Moreoever, done right the mean free path of the electrons is so large in XY plane that they essentially behave as a 2D gas, simply because the layer where they can move is so thin that they can't really move in the Z direction,



How is it that a dot is created because of this?
The gates are used to create an electrostatic potential for the electrons (by applying a negative voltage of the order of a couple of volts); the idea is quite litterally to create an electrostatic well that the electrons can't escape from.
McCloud
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#5
May23-11, 07:46 PM
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Thank you so much for the response. brilliant explaination


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