Semiconductors

in a full wave rectifier, time period becomes half and frequency doubles

The reverse voltage at which a sudden flow of minority carrier increases due to field ionization is called Avalanche Breakdown

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Typical V-I characteristics graph of a silicon diode.

No! Any slab, howsoever flat, will have roughness much larger than the inter-atomic crystal spacing (~2 to 3 Å) and hence continuous contact at the atomic level will not be possible. The junction will behave as a discontinuity for the flowing charge carriers.

C, Si and Ge have same lattice structure. Why is C insulator while Si and Ge intrinsic semiconductors?

The 4 bonding electrons of C, Si or Ge lie, respectively, in the second, third and fourth orbit. Hence, energy required to take out an electron from these atoms (i.e., ionisation energy Eg ) will be least for Ge, followed by Si and highest for C. Hence, number of free electrons for conduction in Ge and Si are significant but negligibly small for C.

(i) Elemental semiconductors: ?

(ii) Compound semiconductors: Inorganic, organic Examples are?