Semiconductors - Carrier Recombination

[Marcin H]

Homework Statement

A sample of Si at room temperature is doped with acceptors at a concentration of 3E16 cm^-3. An excess electron hole pair density of 1E14 cm^-3 is generated at some time t = 0. At t = 13.9 μs the excess EHP density is measured and found to be 5E13 cm^-3.(A). Does the initial excess EHP density satisfy the low-level injection condition? From the given information,
calculate the lifetime of the excess carriers.

(B). Given your answer to part (a), how long will it take for the excess minority carrier concentration to equal the
intrinsic carrier concentration?

(C). Give expressions of n and p as a function of t.

Homework Equations

Low Level Injection

Tn = 1/α(no+po)

The Attempt at a Solution

I am not sure how to begin this problem. How is low level injection related to EHP density? I thought we have to look at majority/minority carriers to determine that?

And for the carrier lifetime how do we find Tn without alpha, or the intrinsic carrier concentrations. I'm not sure how EHP densities can help find that.

 

[Marcin H]

I can find the generation rate by [(1E14 cm^-3) - (5E13 cm^-3)]/13.9us

but this isn't the equilibrium generation rate right? Or is it?