Semiconductor nanotechnology: quantum dots

Micheal Robinson, Micheal McGlen, Will Parr and Josh Conneely

Semiconductors – Micheal

Insulators

Insulators have tightly bound electrons in their outer shellThese electrons require a very large amount of energy to free them for conduction

Let’s apply a potential difference across the insulator above…

The force on each electron is not enough to free it from its orbit and the insulator does not conduct

Insulators are said to have a high resistivity / resistance

Insulators - explained

Insulator – conductor transition

However, if we apply a little heat to the silicon….

An electron may gain enough energy to break free of its bond…

It is then available for conduction and is free to travel throughout the material

We have positive charges too!

Let’s take a closer look at what the electron has left behind

There is a gap in the bond – what we call a hole

Let’s give it a little more character…

Optoelectronics – Micheal “moo”

Lights – Einstein and Planck

1905 Einstein –related wave and particle properties of light

Planck - WAVE-PARTICLES DUALITY

E = h Total E of the Photon (particle side)

Frequency (wave side)

Light is emitted in multiples of a certain minimum energy unit. The size of the unit – photon.

Explain the photoelectric effect - electron can be emitted if light is shone on a piece of metal

Energy of the light beam is not spread but propagate like particles

e

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Quantum mechanics – Will

Bohr’s model

The electron is a wave, it must traverse an integer number of waves in a single orbit of the proton.

To the board we go!!

Quantum dots - Josh

Quantum dots

A quantum dot is a ‘blob’ of one semiconductor embedded in another. The blob is so small that its length scale is close to the electron’s wavelength – so electrons behave as waves.

14Quantum dots from Lancaster

20nm

Electrons are used to image individual atoms…

Quantum networks

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Entangled photon source Quantum memory

To build a secure quantum network we’ll need to be able to store single photons without ‘reading’ them, a quantum repeater. We intend to develop a cheap, scalable repeater using quantum dots.