Physics of Semiconductor Devices

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Minority carrier generation by light

Light shines on silicon at 300 K. The silicon is n-doped at a level of 3 × 1016 cm-3. The light generates 1019 electron-hole pairs per second per cm³. The electron and hole lifetimes are τn = 7 μs and τp = 4 μs.

What is the minority carrier concentration before the light is turned on?

pn0 = cm-3

What is the minority carrier concentration after the light is turned on?

pn = cm-3

After the light has been on for a long time, it is switched off. How long does it take after the light is switched off before the minority carrier concentration reaches 1.1 pn0?

t = s

For silicon, ni = 1.5 × 1010 cm-3 at 300 K.