# Tut 2 - rev 07.08.2015 Page 1 of 4 SOLA2540& SOLA9001...

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rev 07.08.2015 Page 1 of 4 SOLA2540 & SOLA9001 Applied Photovoltaics Tutorial 2 Question 1 The absorption coefficient of silicon decreases from 1.65 × 10 6 cm -1 at 0.3 µ m wavelength to 4,400 cm -1 at 0.6 µ m wavelength to 3.5 cm -1 at 1.1 µ m wavelength. Assuming zero reflection at all wavelengths for the front and rear surfaces, calculate and sketch the generation rate of electron-hole pairs across a silicon cell of 300 µ m thickness, for each wavelength of light, normalized to the surface generation rate in each case. G(x) = α Ne - α x ; G(0) = α N; G(x)/G(0) = e - α x Question 2: A silicon wafer is uniformly doped with 10 16 phosphorus (P) atoms/cm 3 . Assuming that all of these donor impurities are ionised, estimate the density of electrons and holes in this material under thermal equilibrium at 300K. Question 3: In a silicon p-n junction, p and n sides are uniformly doped with 10 16 boron atoms/cm 3 and 5x10 17 phosphorous atoms/cm 3 , respectively. (a) Assuming the hole mobility (in p-side) and electron mobility (in n-side) to be 420 cm 2 /Vs and 650 cm 2 /Vs, respectively and assuming all of the dopants ionised, calculate the resistivity of the p-type and n-type layers. Give your answer in units of [ Ω -cm]. (b) Calculate the built in potential at 300K under thermal equilibrium (assume kT/q = 26 meV). (c) Calculate the total depletion width. How far does the depletion layer extend on the p-side and n-side? (d) Calculate the total depletion width when the p-n junction is biased with an external voltage of 0.5 V (forward bias). Question 4: An intrinsic silicon wafer has a 100cm diameter and 300 µ m thick. a) Calculate the conductivity and resistivity of the wafer. (Assume hole mobility = 450 cm 2 /Vs and electron mobility = 1350 cm 2 /Vs). b) If the wafer is doped with phosphorous concentration of 1 x 10 18 cm -3 , what would be the resistivity of the wafer (assume: all dopants activated; electron mobility = 215 cm 2 /Vs ). c) What would be the current through the wafer if a voltage of 1 V is applied across the wafer in vertical direction.

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