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Quantum Dots : 

Quantum Dots PINSAT ISLAMABAD Presented By: M. Hakim Ali

Outline : 

Outline I. What is quantum dots? II. How to make quantum dots? III. How Quantum Dots Work?

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??? I. What are quantum dots?

Concept : 

Concept Quantum dots are small devices that contain a tiny droplet of free electrons. Quantum dot is a quasi-zero-dimensional nano -material, which is composed of a few atoms. Typical dimensions are between nanometers to a few microns. Generally speaking, Quantum dot is below 100nm in every dimension. It looks like a very tiny dot. The moving of electrons in it are restrained in all directions. quantum confinement effect is severely obvious.

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II.How to make quantum dots?

Method 1chemical colloidal method : 

Method 1chemical colloidal method Can get multilay ered QD Process is simple Abundant CdS/HgS/CdS multilay ered QD by chemical colloidal method HRTEM picture

Method 2self-assembly method : 

Method 2self-assembly method Using molecular-beam epitaxy or chemical vapor deposition By lattice mismatch principle Abundant InAs QD on GaAs substrate by self-assembly method STM picture

Method 3lithography and etching method : 

Method 3lithography and etching method Lithograph and etch by beam of light or electrons Spend long time Not abundant QD(0.5um) on GaAs substrate by lithography and etching method STM picture

Method 4split-gate approach method : 

Method 4split-gate approach method Add outer voltage 2-Dimension Confinement Control gate to change the size and shape of QD. Cannot get production in industry. GaAs/AlGaAs by split-gate approach method STM picture

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III.How Quantum Dots Work? God and we know

A Special Class of Semiconductors : 

A Special Class of Semiconductors Quantum dots, also known as nanocrystals, are a special class of materials known as semiconductors, which are crystals composed of periodic groups of II-VI, III-V, or IV-VI materials. Semiconductors are a cornerstone of the modern electronics industry and make possible applications such as the Light Emitting Diode and personal computer.

A Special Class of Semiconductors : 

A Special Class of Semiconductors Semiconductors derive their great importance from the fact that their electrical conductivity can be greatly altered via an external stimulus (voltage, photon flux, etc), making semiconductors critical parts of many different kinds of electrical circuits and optical applications.

A Special Class of Semiconductors : 

A Special Class of Semiconductors Quantum dots are unique class of semiconductor because they are so small, ranging from 2-10 nanometers (10-50 atoms) in diameter.

A Special Class of Semiconductors : 

A Special Class of Semiconductors At these small sizes materials behave differently, giving quantum dots unprecedented tunability and enabling never before seen applications to science and technology. The usefulness of quantum dots comes from their peak emission frequency's extreme sensitivity to both the dot's size and composition, which can be controlled using Evident Technologies' proprietary engineering techniques. This remarkable sensitivity is quantum mechanical in nature.

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We have every reason to believe that quantum dots will enjoy a shining prospect !

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Thank you