Modeling nonlinearity and noise in high-current photodetectors
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Date
2017-01-01
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Department
Computer Science and Electrical Engineering
Program
Engineering, Electrical
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This item may be protected under Title 17 of the U.S. Copyright Law. It is made available by UMBC for non-commercial research and education. For permission to publish or reproduce, please see http://aok.lib.umbc.edu/specoll/repro.php or contact Special Collections at speccoll(at)umbc.edu
Distribution Rights granted to UMBC by the author.
Distribution Rights granted to UMBC by the author.
Abstract
High-current, high-power photodetectors are important in RF-photonic systems, optical communications systems, photonic microwave generation, and high frequency measurement systems. Device nonlinearity limits the performance of these photodetectors. In order to obtain a linear response with a high output current, we must understand the sources of nonlinearity and find ways to mitigate them. Besides nonlinearity, another important characteristic of photodetectors is the phase noise and amplitude-to-phase (AM-to-PM) conversion. This effect limits the performance of photonic microwave generation systems. We must find the source of AM-to-PM conversion in the photodetectors and find ways to mitigate it. In this dissertations, we first describe one-dimensional (1D) and two-dimensional (2D) drift-diffusion models that we used to study p-i-n, partially depleted absorber (PDA), and modified uni-traveling carrier (MUTC) photodetectors. We obtained excellent agreement with experiments for the harmonic power and responsivity. Impact ionization, external loading, and the Franz-Keldysh effect are all included in the model. In a p-i-n photodetector, we found that impact ionization is an important source of nonlinearity. In a PDA photodetector, we showed that the Franz-Keldysh effect is an important source of nonlinearity. Decreasing the effective load resistor decreases the higher harmonic powers. In an MUTC photodetector, our theoretical calculation agree well with the experimental results. We demonstrated that the dominant physical source of nonlinearity is the Franz-Keldysh effect. We also showed that a shift in the bias null that occurs when the difference frequency is compared to the sum frequency is due to displacement current in the intrinsic region of the device. AM-to-PM conversion in the photodetector occurs due to nonlinearities in the photodetector. We used the impulse response to calculate the phase delay in the photodetector and to analyze the source of AM-to-PM conversion. AM-to-PM noise conversion is due to the change in the transit time that occurs when the pulse energy changes. Our calculations show that the AM-to-PM noise conversion coefficient can be reduced 90% by completely removing the heterojunction between InGaAs and InP. While that is not possible to do in practice, this result demonstrates that it should be reduced as far as possible. In the course of our studies, we have created a computational model for high-current photodetectors. Using this model, we have carried out a detailed study of the field and current evolution in these devices. In addition to its use to analyze the characteristics of existing photodetectors, this model can be used to design new device structures.