can you answer these questions? Describe the difference of direct and indirect s

Question

can you answer these questions?

Describe the difference of direct and indirect semiconductors in terms of energy band structure. Name some popular semiconductor materials of each type. A silicon wafer is uniformly doped with both 10 17 cm-3 of donor atoms and an acceptor concentration of NA. The acceptor energy level is 0.5 eV above the valence band edge, and the donor energy level is 0.2 eV below the conduction band edge. Draw the band diagram with all energy levels; What must ? lambda be for the semiconductor to be exactly compensated at 300 K? The variation of silicon bandgap with temperature can be expressed as Eg(T) = Eg(0) - alpha ?2/(? + ?), where Eg(0) = 1.11 eV, alpha = 4.72 times 10-4 eV/?, and ? = 636 K. Find the band gap of silicon at T = 100K and T = 600K, respectively.

Explanation / Answer

1) In case of a direct band gap semiconductor, the top of the valence band and the bottom of the conduction band occur at the same value of momentum, as in the schematic below.

In case of an indirect band gap semiconductor, the maximum energy of the valence band occurs at a different value of momentum to the minimum in the conduction band energy:

3) Eg at T=100 k

=1.11- (4.72*10^-4*100*100)/(100+636)

=1.11-0.00641

=1.10359 eV

Eg at T=600K

=1.11- (4.72*10^-4*600*600)/(600+636)

=1.11-169.92/1236

=0.9725 eV

  

  

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