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Consider a silicon sample at $T = 300 \: K$, with a uniform donor density $N_d = 5 \times 10 ^{16} cm^{-3}$ , illuminated uniformly such that the optical generation rate is $G_{opt}=1.5 \times 10^{20} cm^{-3}s^{-1}$ throughout the sample. The incident radiation is turned off at $t=0$. Assume low-level injection to be valid and ignore surface effects. The carrier lifetimes are $\tau_{p0}=0.1\mu s$ and $\tau_{n0}=0.5\mu s$.

The hole concentration at $t=0$ and the hole concentration at $t=0.3 \mu s$, respectively, are

1. $1.5 \times 10^{13}cm^{-3}$ and  $7.47 \times 10^{11}cm^{-3}$
2. $1.5 \times 10^{13}cm^{-3}$ and  $8.23 \times 10^{11}cm^{-3}$
3. $7.5 \times 10^{13}cm^{-3}$ and  $3.73 \times 10^{11}cm^{-3}$
4. $7.5 \times 10^{13}cm^{-3}$ and  $4.12 \times 10^{11}cm^{-3}$