- #1
leonmate
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Homework Statement
An abrupt Si p-n junction of cross sectional area 10-4cm-2 has the following properties:
p side:
number densities of acceptor impurity atoms:
NA = 1017cm-3
minority carrier lifetime:
τn = 0.1 us
hole mobility:
μp = 200cm2/Vs
electron mobility:
μn = 700cm2/Vs
n side:
number densities of donor impurity atoms:
NA = 1015cm-3
minority carrier lifetime:
τn = 10 us
hole mobility:
μp = 1300cm2/Vs
electron mobility:
μn = 450cm2/Vs
(I've assumed that μp is hole mobility and μn is electron mobility although I'm not 100% on this)
What is the reverse saturation current Is?
Homework Equations
Reverse saturation current:
Is = eA[(Dhpno / Lh) + (Denpo / Le)]
Where,
Dh = kTμh / e
De = kTμe / e
Lh = √(τhDh)
Le = √(τeDh)
pno = ni2 / NA
npo = ni2 / ND
The Attempt at a Solution
With these equations I should be able to find the reverse saturation current. However, I'm not entirely sure on which values of mobility μ I should be using.
It seems like I can find the reverse saturation current in either the p side or the n side. I thought I'd work it out for both sides and hope that would be equal but I came a little unstuck when finding Lh and Le as it seems I need two values for τ on each side.
In a PN junction, the reverse saturation current is due to the diffusive flow of minority electrons from the p-side to the n-side and the minority holes from the n-side to the p-side.
I feel like I'm lacking some understanding, I was wondering if anyone could help clear this up for me?