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kuski
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Homework Statement
A phosphorus (P) doped Si photoconductor is exposed to far IR radiation of unknown intensity. Its
steady state resistance is found to be 550 Ω. The far IR radiation is then
switched off, and the resistance of the photoconductor takes 20 μs to rise to 1
kΩ. Calculate the
i) intensity of the far IR radiation,
ii) carrier lifetime
Homework Equations
Dimensions of photoconductor = (Lx × Ly × Lz) = 6 mm × 25 mm × 12 mm
(N.B. current is flowing in the x-direction, while the far IR radiation is incident
on the x-y plane of the photoconductor).
Wavelength of IR, λ = 12 μm
Electron mobility μ
e = 2500 cm2 V−1 s−1
Hole mobility μh = 1800 cm2 V−1 s−1
The Attempt at a Solution
My attempt
Since the photoconductor was doped with P, the electron would be the majority carrier. And i equate
I = Area * (eVn + eVp)
= Area * (eVn)
And from this i would get
R= (length/area) 1/(eμn)
Since i have the resistance for steady state and during no illumination
I can apply the above formula with the resistance to find the n created by photons and the intrinsic n.
After which i have no idea what so ever on how to look for the intensity. Please help