EXPLORING QUANTUM DOTS By Amit Kumar Sharma Sai Krishna Priyanka Gupta

EXPLORING QUANTUM DOTS

By

Amit Kumar Sharma

Sai Krishna

Priyanka Gupta

What are QDs

Quantum dots are nano sized semiconductor embedded in another semiconductor.

They are capable of trapping discreet number of electron in a point structure.

They are approx. of the size of 30nm. They have energy band gaps smaller than that of

surrounding materials, hence they trap charge carriers.

The number can be changed by changing the surrounding electric field.

Types of Quantum Dots

Quantum dots are basically of two types:-

a) Gated quantum dots.

b) Self growing quantum dots.

Gated Quantum Dots

These are quantum dots that are at present fabricated using lithography followed by etching.

Success of this method is limited because of technological requirement of producing ultra small structure that are defect free.

Self growing Quantum Dots

In this type a layer of semi conductor over another thin layer of semiconductor material is spread.

Due to difference in lattice, stress is produced which lead to formation of QDs called ‘self growing quantum dots’.

They eliminate the limitation of ‘Gated -QDs’

How

Quantum Dots

Work

Fabrication of Quantum Dots

Gated QDs Fabrication

Silicon nano structures are used . Using of Silicon on insulator (SOI) bring the

size down to 5nm. Using high resolution low energy electron

beam Lithography we prepare Silicon dot structure.

Simultaneously the in plane side gate is formed in thin SOI film.

Gated QDs Fabrication

The etched Silicon is passivated at low temperature.

Contact holes opened in source and drain region by etching.

In this way gated quantum dots are fabricated

Self grown QDs fabrication

Several layers of silicon germanium are arranged in regular arrays.

Due to lattice mismatch between different layers regularly spaced or sized clusters are formed.

They form Si-Ge quantum dots pyramid shaped clusters, which are 100nm wide and 3-10 nanometer tall.

Once the process is initiated they develop self growing tendency hence the name.

Applications

Quantum dots find a number of application in various fields, the most important of

them is in field of telecommunication and computing.

Applications

Applications

A number of QDs can be used to form a cell which is the basic unit.

Each cell will have 4 QDs . In each cell there will be two electrons which occupy the dots in such a way that they are in

lowest energy states. These two states can be used as two states

of digital signal (0 and 1).

Quantum Cells - The Basic Unit

Applications

Quantum Cells - The Basic Unit

The two states can be used as two states of digital signal (0 and 1).

Quantum Cells - The Basic Unit

Applications

The Quantum-cells can be used to

transmit signals just as in a wire.

Applications

Quantum Wires

Applications

Direction of signal propogation

Applications

Direction of signal propogation

Applications

Direction of signal propogation

Applications

Direction of signal propogation

Applications

Direction of signal propogation

Applications

Direction of signal propogation

Applications

Direction of signal propogation

1

Quantum Wires

Advantages: Practically no heat dissipation. Signal remains unaffected by surrounding

EM fields. Hence no signal attenuation takes place

No insulation required. Massive reduction in size.

Applications

Implementing Logic Gates

Logic gates can be implemented using QDs. QD logic gates -three input gates. Majority gates

Applications

THE AND GATE

THE OR GATE

Advantages

Having the three basic gates realized, any logic circuit can be implemented.

The size of logic circuits, thereby, is drastically reduced.

Due to lesser heat dissipation the longevity of the circuits increases.

Applications

Implementing Logic Gates

Single Electron Tunneling (SET) Devices

The best example being electron tunneling transistors.

Reduces the size of transistor to ~20nm.

Applications

Advantages This reduction in size leads to-

1. decrease in switching delays

2. increase in calculation speed

3. drastic decrease in size of transistor based devices such as microprocessors, microcontrollers, ICs, etc

Applications

Single Electron Tunneling (SET) Devices

Conclusion

Thus we conclude that with the advent of Quantum Dots we are about to witness an era where the handhelds will possibly replace the present PCs, IC’s ‘ll shrink to micro dimensions, yielding processing speed comparable or even greater than today’s most advanced processors. Let us all hope for the best.