Question

2. The earth is hit by a mysterious ray that momentarily wipes out all minority carriers. Majority carriers are unaffected. Initially in equilibrium and not affected by room light, a uniformly doped silicon wafer sitting on your desk is struck by the ray at time t = 0. The wafer doping is N, = 1016 / cm3, , = 10-6 seconds, and T=300K. What is An at t = 0+? (t = 0+ is an imperceptible fraction of a second after t=0.) ji. Does generation or recombination dominate at t = 0+ ? Explain. Do low-level injection conditions exist inside the wafer at t = 0+? Explain. i.

Answer 1

Answer -2

   (i) Given,

   N_A = 10¹⁶ / cm³

   So,

     $\small n_{o}=\frac{n_{i}^{2}}{N_{A}}$

  
(1010)2 по 1016

   $\small n_{o}=10^{4}/cm^{3}$

Now,

     $\small \Delta n$   at t = 0⁺  is,

   $\small \Delta n=n-n_{o}=-n_{o}=-10^{4}/cm^{3}$

(ii) Generation dominates at t = 0⁺.

   There is a deficit of carriers at t = 0⁺ and therefore the recombination-generation(R-G) process operates to eliminate the deficit by adding (generating) carriers.

(iii) Yes, low-lwvwl injection conditions exist inside the wafer at t = 0⁺.

   $\small \left | \Delta n \right |=n_{o}=10^{4}/cm^{3}< < p_{o}=N_{A}=10^{16}/cm^{3}$