A) What is the major difference between a direct bandgap semiconductor and an indirect one?
B)Describe a simple method for producing both p-type and n-type semiconductors from silicon?
Solution
A) The energy difference between the minimum energy level of conduction and maximum
energy level of valence band is called band gap of the semiconductor.
The type of alignment between condution and valency band edges of semiconductor with
respective momentum separates the direct and indirect band gaps. In the case of direct bandgap
materials, the maximum energy level of valency band exactly aligns with the lowest energy level
of the conduction band. with respect momentum.
But where in the case of indirect bandgap materials, the lowest energy level of conduction band
does not match with the highest energy level of valency band due to the relative difference in the
momentum.
B) p-type: Doping of silicon with 3rd group elements like gallium (Ga) or Indium (In) can
produce p-type semiconductors.
n-type: Doping of silicon with 4th group elements like phosphorous (P) or Arsenic (As) can
produce p-type semiconductor.