Characterization of semiconductor-based guided wave structures using field theoretical analysis techniques
Date
2018-07-13
Authors
Chen, Shuoqi
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Abstract
In this dissertation, a variety of semiconductor based transmission lines are investigated. Among them are metal-insulator-semiconductor (MIS) coplanar waveguide (CPW) slow-wave structures and laser diodes. Although laser diodes are electro-optic devices, their microwave parameters are of great importance for broadband matching to their driver networks. It will be shown that, besides their optical characteristics, laser diodes can be regarded as bias-dependent lossy and dispersive slow-wave transmission lines for the driving RF/microwave signal.
The analysis of this kind of transmission lines is very difficult or even impossible through a single numerical approach. Therefore, in this thesis a combination of two methods is applied, namely, the complex finite difference method (CFDM) and the frequency-domain transmission line matrix (FDTLM) method. The CFDM provides a self-consistent solution to the semiconductor equations, which determines the conductivity distribution in the semiconductor layer as a function of the bias current. The FDTLM method utilizes this information to calculate the microwave characteristics of such a multilayered, lossy transmission line.
The development of the CFDM, based on information available from the literature, is described in detail. For the FDTLM method, an investigation is presented analyzing the errors of the various node representations. On the basis of this investigation, a new node, the hybrid node with shunt decomposition, is developed. This node shows better accuracy than other nodes and is particularly well suited for the analysis of lossy, semiconductor-based structures. Furthermore, by using finite differencing and averaging, the theoretical foundation of the FDTLM method is expanded and, for the first time, a direct relationship between the electromagnetic field and the voltages and currents in the hybrid node with shunt decomposition is established.
On the basis of the numerical techniques developed in the first part of the thesis, mode propagation and scattering of electromagnetic field in a variety of semiconductor-based structures are investigated. Besides the microwave effects in semiconductor lasers and the slow-wave characteristics in MIS CPW structures, the second part of this thesis concentrates on the scattering of fields at discontinuities between transmission lines. This includes wire bond and flip-chip transitions between transmission lines and laser diodes as well as direct transitions, for example, between slow-wave CPW structures on doped silicon and CPW on the same but an undoped substrate.
Whenever possible, these results are compared with those from other methods and measurements. However, since most of the structures and transitions considered in this thesis are investigated for the first time, the data available in the open literature is limited. From the comparison of obtained results with the available data and measurements one can safely conclude that the numerical analysis presented for all structures is a true picture of the physical reality.
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Keywords
Semiconductors, Electric lines, Wave guides