Question

question 3

1. A photoconductor is made of n-type silicon with conductivity of 3 Scm1 and recombination lifetime of 50 μs, when illuminated with light, the conductivity of the photoconductor increases to 5 Scm1. Find the electron-hole pairs recombination rate during illumination. r the photoconductor described above, find energy difference between quasi-Fermi levels before illumination and during illumination. 2. Fo 3. For the photoconductor described above, estimate mean free time, mean free path and the magnitude of the applied electric field if the drift velocity of electrons is 50 m/s. 4. For the photoconductor described above, estimate diffusion lengths for electrons and holes before and during illumination

Answer 1

Given n-Type silicon. sigma = 3 s/cm tau = 50 mu s v_d = 50 m/s = 50 times 10^2 cm/s mu = e tau/m = 1.6 times 10^-19 times 50 times 10^-6 m^2/v middot s mu = 1.6 times 50/9.1 times 10^6 = > mu 8.89 times 10^6 m^2/v middot s mu = 889 cm^2/v middot s v_d = mu E = > E = < vd/mu = 50 times 10^2 cm/s/889 cm^2/v middot s E = 5.62 v/cm leftarrow applied field Mean free Time = 50 mu s rightarrow when not illuminates when illuminated sigma = 5s/cm \r\n Before illumination sigma = n e^2/m tau 3 s/cm = n times (1.6 times 10^-19)^2/9.1 times 10^-31 times 50 times 10^-6 eta = 3 times 9.1 times 10^-31/(1.6)^2 times 10^-38 times 50 times 10^-6 eta = 0.213 times 10^13/cm Calculation of Mean free Time after illumination sigma = ne^2/m tau 5 s/cm = 0.213 times 10^13 times (1.6 times 10^-19)^2