EXPLORING QUANTUM DOTS

1. EXPLORING QUANTUM DOTS By Amit Kumar Sharma Sai Krishna Priyanka Gupta

2. 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.

3. Types of Quantum Dots Quantum dots are basically of two types:- a) Gated quantum dots. b) Self growing quantum dots.

4. 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.

5. 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’

6. How Quantum Dots Work

19. Fabrication of Quantum Dots

20. 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.

21. 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

22. 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.

23. Applications

24. Applications Quantum dots find a number of application in various fields, the most important of them is in field of telecommunication and computing.

25. Applications Quantum Cells - The Basic Unit • 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).

26. Applications Quantum Cells - The Basic Unit

27. Applications Quantum Cells - The Basic Unit The two states can be used as two states of digital signal (0 and 1).

28. Applications Quantum Wires The Quantum-cells can be used to transmit signals just as in a wire.

29. Applications Direction of signal propogation 

30. Applications Direction of signal propogation 

31. Applications Direction of signal propogation 

32. Applications Direction of signal propogation 

33. Applications Direction of signal propogation 

34. Applications Direction of signal propogation 

35. Applications 1 Direction of signal propogation 

36. Applications 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.

37. Applications Implementing Logic Gates • Logic gates can be implemented using QDs. • QD logic gates -three input gates. • Majority gates

38. THE AND GATE

48. THE OR GATE