a)  Sketch the variation of electron concentration with temperature for

i)  an n-type semiconductor doped with 1021  donors m-3

ii)  an intrinsic semiconductor.

 b)  Explain briefly why the intrinsic carrier concentration at a given temperature is greater for germanium than for silicon. 

c)  At a temperature of  293 K an intrinsic semiconductor has an electron mobility of  0.12 m²V^-1s^-1 and a hole mobility of 0.07 m²V^-1s^-1.

If its resistivity is 35 :m, calculate the intrinsic carrier concentration. Hence calculate the hole concentration when the semiconductor is doped with 1021 donors m^-3.  

d)  If a voltage of 0.5 V is applied across the opposite faces of a sample of the above intrinsic semiconductor (in part c) of thickness 0.2 mm, determine the approximate total current density and the average drift velocity of the holes.