High speed photodetectors are a necessary element in
broad band digital and analog optical communication systems.
In this thesis easily integrable planar high speed
photodetectors made on undoped semi-insulating (SI) GaAs
substrates are modeled and tested. The fabrication process
of the detectors is fully compatible with GaAs
metal-semiconductor field effect transistor (MESFET)
processing technology. Interdigitated fingers are used as
the contacts to achieve both high sensitivity and large
bandwidth. Detectors made with both ohmic and Schottky
contacts are fabricated and tested.
The equivalent circuit elements of the interdigitated
structure are modeled using accurate lumped element circuit
models associated with the various discontinuities of the
structure. The results of the model agree well with the
experimental results as well as with other published
results. Numerical simulation of the SI-GaAs metal-semiconductor-
metal (MSM) photodetector is performed. The
carriers are tracked after an ideal optical pulse is applied
and the intrinsic current as a function of time is computed.
Then the influence of all the external circuit elements is
included and the output current across the load resistor is
computed. The simulated response is compared with other
published models.
The electrical and optical characteristics of the
detectors are measured. For ohmic contact detectors, the
dark current increases linearly with bias until some
critical field is reached beyond which the dark current
increases nonlinearly with bias. The time response of the
detectors is measured with a 10 ps pulsed laser operating at
- 600 nm and also with a pulsed GaAs /AlGaAs semiconductor
laser operating at 850 nm. The ohmic and Schottky contact
detectors have approximately the same rise time. The fall
time of the Schottky contact detector is much smaller than
the fall time of ohmic contact detector. The long fall time
of the ohmic detector does not depend on the spacing between
contacts. This long fall time is due to the large barrier
that exists near the ohmic metal/SI-GaAs cathode contact. No
such barrier exists for SI-GaAs MSM photodetector. The
simulated impulse response of the SI-GaAs MSM photodetector
is compared with the measured impulse response. / Graduation date: 1991
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/37481 |
| Date | 12 April 1991 |
| Creators | Kollipara, Ravindranath Tagore |
| Contributors | Plant, Thomas K. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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