2What are QDsQuantum 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.
3Types of Quantum Dots Quantum dots are basically of two types:- a) Gated quantum dots.b) Self growing quantum dots.
4Gated Quantum DotsThese 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.
5Self 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’
20Gated 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.
21Gated QDs FabricationThe 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
22Self 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.
24ApplicationsQuantum dots find a number of application in various fields, the most important of them is in field of telecommunication and computing.
25Quantum Cells - The Basic Unit ApplicationsQuantum Cells - The Basic UnitA 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 whichoccupy 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).
26Quantum Cells - The Basic Unit ApplicationsQuantum Cells - The Basic Unit
27Quantum Cells - The Basic Unit ApplicationsQuantum Cells - The Basic UnitThe two states can be used as two states of digital signal (0 and 1).
28The Quantum-cells can be used to transmit signals just as in a wire. ApplicationsQuantum WiresThe Quantum-cells can be used totransmit signals just as in a wire.
36Applications Quantum Wires Advantages: Practically no heat dissipation.Signal remains unaffected by surrounding EM fields. Hence no signal attenuation takes placeNo insulation required.Massive reduction in size.
37Implementing Logic Gates ApplicationsImplementing Logic GatesLogic gates can be implemented using QDs.QD logic gates -three input gates.Majority gates
58Implementing Logic Gates ApplicationsImplementing Logic GatesAdvantagesHaving 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 longevityof the circuits increases.
59Single Electron Tunneling (SET) Devices ApplicationsSingle Electron Tunneling (SET) DevicesThe best example being electron tunneling transistors.Reduces the size of transistor to ~20nm.
60Single Electron Tunneling (SET) Devices ApplicationsSingle Electron Tunneling (SET) DevicesAdvantagesThis reduction in size leads to-1. decrease in switching delays2. increase in calculation speed3. drastic decrease in size of transistor based devices such as microprocessors, microcontrollers, ICs, etc
61ConclusionThus 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.