Abstract:
Optical receiver front-end modules are key components in every light wave communication
system. The very first part of this module is PiN photo-diode which plays important role in
sensitivity of the system in optical communication. This sensitivity and selectivity is governed by
tailoring the geometry and material selection of the device. Light sensitive area of PiN photodetector is its intrinsic absorption region. In this thesis 2D simulation work of InGaAs/InP
photodiode is presented using Sentaurus Synopsys Technology Computer Aided Design (TCAD)
software. The absorption region thickness is varied from0.2µm to 4um with a step of 0.2µm to
check for different dark currents and Photon absorption densities. The dark current varies from
0.4nA/µm to 6nA/µm for i-region thickness of 0.4µm to 3.8µm respectively at 12 volts reverse
biased. The device possesses high breakdown voltage below -25 volts which makes it safe to use
within low voltage range. Ray trace optical model is used to calculate photon absorption rate in
the device. Photon absorption density increases with increase in absorption region thickness. The
results satisfy the above mention statement and photon absorption density turned out to be
1.8x1022 /µm and 4x1022 /μm for i-region thickness of 1μm and 4μm respectively. Similarly
responsivity increases with increase in absorption region at biased voltage of -12 volts and
wavelength of 1.6µm. The capacitance is the major source of noise in photo detectors as the
frequency is limited by RC time constant factor. The capacitance of the device is simulated
0.38fF and 1.8fF for thicknesses of 1µm and 4µm respectively. Increase in i-region thickness
decreases the capacitance but on the other hand it increases the dark current. Literature reveals
that increase in absorption region thickness also decrease the band-width of the device which is
critical factor when using PiN diode as an optical receiver front end. The band width for 2µm iregion thickness is calculated 13.5 GHz while for 3.8µm thickness is just 7.1 GHz. So there is
trade-off between dark current, bandwidth and photon absorption density. The optimum i-region
thickness would turn out to be around 3µm. Device can be tailored be keeping these parameters
in view to achieve desired results.
