Anita was thinking that C, Si and Ge have same lattice structure, but C is insulator while Si and Ge are intrinsic semiconductors. For its answer she met her friend Sunita. Sunita explained her that the four bonding electrons of C, Si and Ge lie respectively in the second, third and fourth orbit. So, energy required to take out an electron from these atoms known as ionisation energy Eg, will be the least for Ge, followed by Si and the highest for C. Hence number of free electrons for conduction in Ge and Si are significant while negligibly small for C.
(a) What are the values Shown by Sunita?
(b) If a pure silicon crystal has 5 x 1028 atoms/m3 . It is doped by 1ppm concentration of pentavalent arsenic.
If ni = 1.5 x 1016/m3 then calculate the number of electrons and holes.
