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It is well known that the performance of modern photodiodes is determined by three
basic parameters: sensitivity, response time and noise equivalent power (NEP). In
practical situations it is almost always necessary to achieve the maximum product of
sensitivity and reciprocal response time (bandwidth). At low Continuous Wave (CW)
light incidence, a photodiode gives a signal proportional to optical intensity. But with
increasing light power, photocurrent deviates from a linear behavior. High-linear
performance is becoming increasingly important for photodiodes because high
photocurrents directly translate into an increased dynamic range and reduced noise figure.
This is crucial for many photonic systems, including photonic analog-to-digital
converters and high-bit-rate digital receivers. The increase of photocurrent depends on
two primary factors: one is space-charge limitations, which are influenced by device
physical dimensions, structure type, illumination conditions, maximum electric field, and
the other is thermal considerations. From the view of long-term reliability of photodiodes,
thermal effects are crucial because it results in device failure due to dark current runaway.
As known to us, there have many reports on the thermal effect originating from InGaAs
intrinsic region. However, nonlinearity originating from both InGaAs intrinsic region and
contact resistance is still unclear. In some cases, the contact resistance between metal
electrode and semiconductor is not negligible. In this report, N type heavily doped InP
single crystal is used as a substrate, on which a buffer layer of n doped InP is grown.
Then the intrinsic absorbing layer of InGaAs, and finally a transparent InP cap layer are
deposited with MOCVD technique. A circuit model has been developed and the
nolinearities of PIN photodiodes has also been discussed.
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