Physics of Semiconductor Devices

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How does a solar cell work? - Exam January 2012

How does a solar cell work?

(a) Explain which way the current flows.
(b) Why are GaAs solar cells (Eg = 1.42 eV) more efficient than Si solar cells (Eg = 1.1 eV)?
(c) Does it matter if the semiconductor has a direct or indirect band gap? Why or why not?
(d) What can be done to make sure that most of the photons are absorbed in the depletion layer?