# Help! Current generated by an alpha particle in silicon(reverse bias voltage problem)

1. Dec 4, 2011

### neural_jam

Hi all, me again!

I'm trying to calculate the current created when an alpha particle strikes a silicon p-n detector, but I'm getting some strange numbers, so I was wondering if I was doing something fundamentally wrong...

My problems start when I try to calculate the reverse bias voltage required to create a depletion region equal to the range of alpha particles in Si, which I understand to be 7.29x10-5m.

I use the following equation:

d= $(\frac{2 \epsilon V}{e N})^{\frac{1}{2}}$

where d is the depletion region (m) = 7.29x10-5
ε is the ionisation energy of Si @ 300K (eV) = 3.62
e is the charge on an electron (C) = 1.602x10-19
N is the charge carrier number density (m-3) = 1019
and V is the bias voltage.

rearranging I get

V = $\frac{d^{2}eN}{2\epsilon}$

So far, so simple.

However, for some reason, after plugging the numbers in I get ~1.18x10-9V for the bias voltage, which seems to be very small

So can anyone tell me what I'm doing wrong? Or is it right and my expectation of a voltage in the 10s of volts wrong?

Thanks!