IV.22 - Non-silicon PIN photodiodes?

This section was contributed by Kathy Meehan, meehan@srvr.third-wave.com.

A p-i-n photodetector is a diode with an large (~2um thick) intrinsic layer between the p and n-type regions. The cut-off wavelength (the longest wavelength detected) of the diode is dependent on the bandgap of the intrinsic layer. The cut-on wavelength (the shortest wavelenght detected) is usually determined by the p-type material for a front-illuminated detector or the n-type material for a back-illuminated diode. These type of devices cover the spectral region from the near-UV to mid-IR. A novel type of detector being used in the 3-5um region is a QWIP which absorbs light via intraband absorption, not interband. Two types of detectors in the far-IR are extrinsic detectors and photoconductors. The first absorbs light by generating an electron or hole from a trap or dopant level. The second relies on the change in resistance caused by illumination.

The responsivity (amps generated per watt of light) is a function of the energy of the photon (packet of light), the quality of the intrinsic layer and the quality of the p-i and i-n interfaces. The latter two determine the lifetime of the electrons and holes generated by the photon and whether or not they make it into the p or n-type material. Light-generated electrons and holes that recombine in the intrinsic region do not contribute to a measureable current. The capacitance is determined by the area of the p region, the dopant level of the intrinic region and stray capacitance from bonding pads, etc. The resistance is determined by the contact resistance, the spreading resistance in the p layer and the shunt resistance of the p-i-n layer which is a function of bandgap, background doping and defect levels. The speed of the detector is limited by the carrier lifetime which in turn impacts effective area of the detector. Reverse biasing the p-i-n to make the depletion width equal to the thickness of the i region, decreases the rise and fall times.

Standard Telecommunication Detectors:

• Telcom Devices, 829 Flynn Drive, Camarillo, CA
• AMP/Lytel, 61 Chubb Way, Somerville, NJ (908) 685-2000
• Epitaxx, 7 Graphics Drive, West Trenton, NJ 08628 (609) 538-1800

Linear Arrays:

• Hamamatsu, 360 Foothill Road, P.O. Box 6910, Bridgewater, NJ 08807-6910 (908) 231-0960
• EG&G Optoelectronics, 221 Commerce Drive, Montgomeryville, PA 18936 (215) 368-6900
• Epitaxx, 7 Graphics Drive, West Trenton, NJ 08628 (609) 538-1800
• Sensors Unlimited, 3490 US Rte. 1, Bldg 12, Princeton, NJ 08540 (609) 520-0610

Extended InGaAs and HgCdTe

• Fermionics, 4555 Runway Street, Simi Valley, CA 93063 (805) 582-0155
• Sensors Unlimited, 3490 US Rte. 1, Bldg 12, Princeton, NJ 08540 (609) 520-0610
• Hamamatsu, 360 Foothill Road, P.O. Box 6910, Bridgewater, NJ 08807-6910 (908) 231-0960
• Epitaxx, 7 Graphics Drive, West Trenton, NJ 08628 (609) 538-1800

Associated Technologies

• Photoconductors
  Optoelectronics, Grasby, CalSensors, SensArray, NEP, Hamamatsu
• Fiber Optics
  Spectran, 3M, Corning, Cermoptics
• Si-based IR detectors: bolometers, pyroelectric detectors. Platinum Silicide
  GEC-Marconi, Texas Instruments, Kodak, David Sarnoff Laboratories