Page 63 - Photonics Essentials an introduction with experiments

Photodiodes

Photodiodes 57

The performance of photodiodes is determined by four properties:
quantum efficiency, range of spectral sensitivity, response time, and
noise. We have considered the first two properties in this chapter. The
response time of a photodiode will be determined in most applications
by the product of the photodiode capacitance and the series resistance
of the measuring circuit and is discussed next in Chapter 4. The effect
of detector properties on system noise can be related to the dark cur-
rent and the capacitance. See the Bibliography of this chapter for a
treatment of the noise generated in photodetection.
The quantum efficiency of a photodiode with a properly designed
structure is close to 100%. Reflections due to the difference in index of
refraction between the semiconductor and air lead to a reduction of
25% in the quantum efficiency. The use of an antireflection coating
can entirely eliminate this effect, but only in a narrow wavelength
range. The spectral sensitivity covers the entire spectral range having
a wavelength shorter than the optical wavelength corresponding to
the band gap energy.

Bibliography
C. R. Wie, “The Semiconductor Applet Service,” http://jas.eng.buffalo.edu/ap-
plets/. A truly outstanding set of applets on semiconductor physics and de-
vices has been written by Prof. Chu R. Wie of the University of Buffalo. In
addition, at this URL you will find links to many other related Web sites for
semiconductor device applets. Bookmark this now!
P. K. Bhattacharya, Semiconductor Optoelectronic Devices, Prentice-Hall, En-
glewood Cliffs, 1994.
G. W. Neudeck, The PN Junction Diode, 2nd ed., Addison-Wesley, Reading,
1989.
A. Rose, Concepts in Photoconductivity and Allied Problems, Wiley-Inter-
science, New York, 1963). This short book of 168 pages may be the best you
will ever find on photodetection. I emphasize find, because it has been out
of print for years. The cover is an unimposing mousey beige. Keep your
eyes peeled for this at garage sales or in the discard pile of retiring profes-
sors. If you find it, buy it. Price should be no object.
W. T. Tsang (Ed.) Lightwave Communications Technology: Photodetectors,
Semiconductors and Semimetals, Vol. 22D, Academic Press, Orlando,
1985.
A. Yariv, Optical Electronics in Modern Communications, Oxford University
Press, New York, 1997.

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