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ENERGY DEVICES - Coggle Diagram

- - - - invented by Britich chemist, John Frederic Daniell.
        
        Zn electrode dipped in ZnSO4 solution:
        Oxidation: Zn → Zn^2+ + 2e-
        
        Cu electrode dipped in CuSO4 solution:
        Reduction: Cu^2+ + 2e- → Cu
        
        each electrode >> half cell >> connected through salt bridge.
        
        salt bridge: KCl or NH4Cl in a gelatine form.
        
        salt bridge maintains the charge balance in the two half cells. minimizes or eliminates liquid junction potential.
        
        cell emf = 1.1V
    - - electromotive force (EMF): maximum potential difference between two electrodes of a galvanic or voltaic cell.
        
        related to tendency for an element, a compound or an ion to acquire (gain) or release (lose) electrons.
        
        cell reaction is feasible when Ecell has positive value.
        
        cell EMF in terms of Nernst equation:
  - - - Na+ ions gain electrons and are reduced at the cathode.
        
        as Na+ ions near the cathode are depleted, additional Na+ ions migrate in.
        
        Cl- ions lose electrons and are oxidized to Cl2 at the anode.
        
        positive terminal is connected to anode.
        
        negative terminal is connected to the cathode which forces electrons to move from the anode to cathode.
        
        electrolysis is performed at ~801 degrees celsius.
        
        inert electrodes are used.
    - - a pair of inert electrodes are dipped into the solution and applying a voltage between them results in the rapid evolution of bubbles of H2 and O2.
        
        due to very poor electrical conductivity of pure water, a small amount of an ionic solute (such as H2SO4 or Na2SO4) is added to increase its electrical conductivity.
        
        the electrolytes are chosen such a way that the ions that are harder to oxidize or reduce than water:
        Cathode: 4 H+(aq) + 4 e- → 2 H2(g)
        Anode: 2 H2O → O2(g) + 4 H+ + 4 e-
        Overall: 2 H2O → O2(g) + 2 H2(g)
- - - - pentavalent impurity - P, As, Sb etc.
    - - trivalent impurity - B, Al, In etc.
  - - - Distillation
        
        difference in boiling points.
        
        for Ge >> GeCl4 and for Si >> SiHCl3
      - Zone Refining
        
        difference between solubiity of impurities in the molten and solid phases is used to concentrate impurities at the end section of ingots.
        
        metal crystallizes while impurities remain in a molten state (mass) or melt.
        
        polycrystalline Ge or Si obtained.
      - Czochralski Crystal Pulling Technique
        
        growing the crystal on a single crystal seed.
        
        atoms reproduce identical atomic arrangement as that of the seed crystal.
    - - Epitaxy
        
        unified crystal growth or deposition of a thin crystal on another substrate.
      - Diffusion Technique
        
        conversion of a region of semiconductor material by a solid or gaseous diffusion of impurity atom into the crystal lattice of the semiconductor material without any melting.