IV.12 - Avalanche Photodiodes (APD's)?

Yuan Jiang, yjj@eng.umd.edu, says:

• An avalanche photodiode is essentially a PIN or PN photodiode operating at high reverse bias. At such a high bias, the free carriers (electrons and holes) in the depletion region are accelerated to high speeds. Such a carrier with high kinetic energy can excite an electron in the valence band to the conduction band and, therefore, create an electron and a hole. This one-carrier -> three-carrier process is called impact ionization process or avalanche process. As a result, the current is amplified.

  With the built-in current amplification, APDs are used for detecting low optical signals in applications such as long-distance fiber communications, spectrometry, laser radars and etc. The theory of APDs is well studied in the classical paper by R. J. McIntyre (IEEE Transactions on Electron Devices, vol. ED-13, p.164, 1966). Ge and Si APDs are reviewed by G. E. Stillman and C. M. Wolfe (in Semiconductors and Semimetals, vol. 12, p. 291, 1977, R. K. Willardson and A. C. Beer, eds. Academic Press, New York). InGaAsP/InP APDs are reviewed by T. P. Pearsall and M. A. Pollack in vol. 22D (1985) of the above series. In the same volume, F. Capasso reviews the impact ionization processes in IV-V compound semiconductors.

  Si, Ge and InGaAsP/InP APDs are commercially available. Beside the apparent differences in their wavelength range of sensitivities, Si APDs have much lower noises and dark currents and are the choice for detecting 1 micron or shorter wavelength light. Although both InGaAsP/InP and Ge APDs can detect light of 1.6 micron or shorter wavelength, InGaAsP APDs have lower dark currents. Most manufacturers that make PIN or PN photodiodes also make APDs.

interesting note added by Dave Kirkby, davek@medphys.ucl.ac.uk :

• APD's, since their gain is dependent on the bias voltage, can be gain modulated by adjusting the bias voltage. Since the temporal response of an APD is limited usually not by RC time constant, but by the time for carriers to diffuse, it's possible to achieve a faster temporal response when using a gain modulated diode, since you can modulate as fast as RC time constant allows. I've achieved temporal response in a cross correlator of 275ps FWHM from an APD that has a temporal reposone when biased with DC of only 750ps FWHM. Bias was modulated with a pulse from an SRD.
• D. R. Kirkby et al, "Measurement of Tissue Temporal Point Spread Function by use of an Cross-Correlation technique using an Avalanche Photodiode", Paper 2389-24 (in press), Proc. SPIE conference on Biomedical Optics, 4-10th Feb 1995, San Jose, California, USA.

Si APDs:

• Advanced Photonix, 1240 Avenida Acaso, Camarillo, CA 93012
  Phone: (805) 987-0146
  Fax: (805) 484-9935
  
• EG&G Optoelectronics Canada, 22001 Dumberry Road,
  Vaudreuil, Quebec, J7V 8P7 Canada
  Phone: (514) 424-3300
  Fax: (514) 424-3411
  
• Hamamatsu Photonics K.K., Solid State Division,
  1126-1, Ichino-cho, Hamamatsu City, 435, Japan
  Phone: 053-434-3311
  Fax: 053-434-5184
  

  Hamamatsu Corp. (USA), 360 Foothill Road,
  POB 6910, Bridgewater, NJ 08807-0910
  Phone: (908) 231-0960
  Fax: (908) 231-1218
  

• Hitachi America, Ltd, Semiconductor and IC Division, Hitachi Plaza,
  2000 Sierra Point Parkway, Brisbane, CA 94005-1819
  Phone: (415) 589-8300
  Fax: (415) 583-4207
  
• Radiation Monitoring Devices, 44 Hunt Street, Watertown MA 02172
  Phone: (617) 926-1167
  Fax: (617) 926-9743
  

Si APDs packaged with receiver circuits:

• EG&G Optoelectronics Canada, Hamamatsu (see addresses above)
  

Ge APDs:

• Germanium Power Devices Corp, 300 Brickstone Square,
  York Str., Box 3065, Shawsheen Volliage Station,
  Andover, MA 01810-3065
  phone (508) 475-5982
  fax (508) 470-1512
  

InGaAsP/InP APDs:

• EG&G Optoelectronics Canada, Germanium Power Devices, Hitachi
  (see addresses above)