Page 106 - Photonics Essentials an introduction with experiments

Photoconductivity

100 Photonic Devices

Problems
5.1 A light pulse from a laser ( = 600 nm) with a duration of 1
nanosecond and an intensity of 10 –7 W is absorbed by a Si photo-
2
conductor having an area of 1 cm . How many electron hole pairs
are created?
5.2 Using energy-level diagrams, explain why the maximum photo-
conductive gain is unity in a photodiode.
2
5.3 A Si photoconductor having an area of 1 cm and a thickness of 2
microns is uniformly illuminated by a steady state beam of pho-
tons with energy 2 eV. The intensity of the light beam is 1 mi-
crowatt. Consider that all the light is absorbed. If the lifetime of
electron hole pairs is 1 microsecond, determine the steady-state
photo-excited carrier concentration.
5.4 Illustrate the photoconductive process in photography by using
energy level diagrams to describe the three steps shown in Figs.
5.10 through 5.12.
5.5 Following the example in Eqs. 5.18 through 5.23, calculate the
hole lifetime as modified by sensitization.
5.6 Consider the sensitization of the photoconductor discussed in the
2
text with a level having the property that s n2 = 10 –15 cm , and s p2
2
= 10 –17 cm . Consider that all other parameters remain the
same. Calculate the electron lifetime and the hole lifetimes of
the sensitized photoconductor.

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