| Summary: | 碩士 === 國立清華大學 === 電機工程學系 === 85 === Abstract
There are two major parts in this thesis. One is to calibrate
the newly setup SEM lithography system and to apply it to
the fabrication of submicron Metal-Semiconductor-
Metal (MSM) photodetectors. The other is to setup a
comprehensive model to analyze the photocurrent response of
GaAs MSM schottky photodiodes.
In the first part, the frame size was first calibrated, and the
backlash of the motor stage, the dwell time, the step size,
as well as the probe current were then optimized. Other
factors such as the thickness of PMMA, the baking condition,
the exposure procedure, the metal thickness, the
proximity effects, and then the focusing were also investigated.
With all these optimization procedure, we succeeded in
fabricating MSM photodetector with submicron metal line width
and various spacing. In the second part
of this thesis , the photoresponse of the MSM
photodetectors was analyzed with 2-D simulator. Our simulation
of the carrier transport in these structures reveals the
strong influence of distance between the finger
electrodes, the external voltage, the GaAs layer thickness, the
temperature and the excitation intensity on the intrinsic
response time and the corresponding frequency bandwidth of these
photo detectors.We also calculated the performance for
intrinsic devices with 0.5um interdigital spacing with the
corresponding equivalent circuit of the photodetector. It is
pointed out that parasitic effects may induce a
significant distortion and a delay of intrinsic response. These
can be minimized by choosing the optimal photodetector
capacitance. Our results are consistent with that reported in
the literature.Finally, nonuniform illumination to
generate electric pulses from the transmission lines was
also studied and a 3THz bandwidth was found for the transmission
lines with 20um linewidth and spacing.
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