5. A bar of Ge is doped with phosphorous at a concentration of 10^16cm^-3. It is

Question

5. A bar of Ge is doped with phosphorous at a concentration of 10^16cm^-3. It is exposed to light so that electron-hole pairs are generated throughout the volume of the bar at the rate of 10^19/s·cm^3. The recombination lifetime is 2us. Find p0 , n0 , p’, n’, p , n, and the np product.

A bar of Ge is doped with phosphorous at a concentration of 10^16cm^-3. It is exposed to light so that electron-hole pairs are generated throughout the volume of the bar at the rate of 10^19/s-cm^3. The recombination lifetime is 2mus. Find p_0, n_0, p', n', p, n, and the np product.

Explanation / Answer

a)

equilibrium hole concentration

po=Na=1016 cm-3

b)

For Ge ni=2*1013 cm3

equilibrium electron concentration

no=ni2/po = (2*1013)2/1016 =4*1010 cm-3

c)

In steady state ,the rate of regeneration is equal to rate of recombination

p'/T =1019/s cm3

p' =1019*2*10-6

p' =2*1013 cm-3

d)

n'=p'=2*1013 cm-3

e)

p=po+p' =1016+2*1013=1.002*1016 cm-3

f)

n=no+n' =4*1010 +2*1013 =2.004*1013 cm-3

g)

np=(1.002*1016 )(2.004*1013)=2.008*1029 cm-6

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