Page 368 - Introduction to Information Optics

Exercises

6.9 A Ge detector is to be used for an optical communication system using a
GaAs laser with emission energy of 1.43 eV. Calculate the depth of the
detector needed to be able to absorb 90% of the optical signal entering
l
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the detector. The absorption coefficient a is given to be 2.5 x 10 cm~ .
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6.10 An optical intensity of 10 W/cm at a wavelength of 0.75 /mi is incident
on a GaAs detector. Calculate the rate at which electron-hole pairs will
be produced at this intensity at 300 K. If the electron-hole combination
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time is 10~ s, calculate the excess carrier density. The absorption
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1
coefficient of GaAs at 0.75 jum is 7 x 10 cm" . 0.75 yum wavelength is
equivalent to a photon of 1.65 eV.
6.1.1 Consider a long silicon p-n junction that is reverse biased with a
reverse-bias voltage 2 V. The diode has the following parameters (all at
300 K):

Diode area, A
p-side doping
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n-side doping N d= 10 cm~ 3
2
Electron diffusion coefficient £>„ = 20 cm /s
2
Hole diffusion coefficient D p = 12cm /s
Electron minority carrier lifetime
Hole minority carrier lifetime
3 !
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Electron-hole pair generation rate G L= 10 cm^ s
Calculate the photocurrent.