Theoretical aspects of polysilicon emitter biopolar transistors
Theoretical aspects of polysilicon emitter biopolar transistors
This thesis is devoted to a theoretical study of polysilicon emitter bipolar transistors, and in particular to such transistors which do not have a single crystal region as part of the emitter. A related topic concerning the modelling of surface recombination is also discussed. A model for a polysilicon emitter bipolar transistor, whose emitter drive-in has been low enough so that there is no single crystal part to the emitter, is presented in chapter 3. Both direct, and trap-assisted, tunnelling mechanisms are considered in detail, so that the model is versatile enough to handle a variety of configurations for the potential barrier presented by the interfacial layer. The results predicted by this model are compared with experimental results for such a device, in chapter 4. A good fit to the experimental results is obtained, and a full study of the effect of varying the physical parameters of the model is made. It is found that the poorer current gain displayed by this kind of device (as compared to an equivalent transistor with a single crystal region as part of the emitter), is due to increased recombination at the interface. However, a very large gain (in excess of 10,000) is predicted, for this type of device, if the interface state density is lowered sufficiently (to a value of 109 cm-2, or below). The cause of a pronounced kink in the base current characteristic, which is observed experimentally, is fully explained and furthermore it is shown that this can lead to a negative differential resistance regime for certain parameter values. The validity of replacing a (more physically realistic) spectrum of interface states, by a single trapping level, as regards the recombination rate, is investigated in chapter 5. This is done for both a uniform, as well as an energy-dependent spectrum, and for both energy-dependent and energy-independent capture coefficients. It is found that considerable errors may be incurred if such an approximation is adopted.
University of Southampton
1988
Browne, David Charles
(1988)
Theoretical aspects of polysilicon emitter biopolar transistors.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
This thesis is devoted to a theoretical study of polysilicon emitter bipolar transistors, and in particular to such transistors which do not have a single crystal region as part of the emitter. A related topic concerning the modelling of surface recombination is also discussed. A model for a polysilicon emitter bipolar transistor, whose emitter drive-in has been low enough so that there is no single crystal part to the emitter, is presented in chapter 3. Both direct, and trap-assisted, tunnelling mechanisms are considered in detail, so that the model is versatile enough to handle a variety of configurations for the potential barrier presented by the interfacial layer. The results predicted by this model are compared with experimental results for such a device, in chapter 4. A good fit to the experimental results is obtained, and a full study of the effect of varying the physical parameters of the model is made. It is found that the poorer current gain displayed by this kind of device (as compared to an equivalent transistor with a single crystal region as part of the emitter), is due to increased recombination at the interface. However, a very large gain (in excess of 10,000) is predicted, for this type of device, if the interface state density is lowered sufficiently (to a value of 109 cm-2, or below). The cause of a pronounced kink in the base current characteristic, which is observed experimentally, is fully explained and furthermore it is shown that this can lead to a negative differential resistance regime for certain parameter values. The validity of replacing a (more physically realistic) spectrum of interface states, by a single trapping level, as regards the recombination rate, is investigated in chapter 5. This is done for both a uniform, as well as an energy-dependent spectrum, and for both energy-dependent and energy-independent capture coefficients. It is found that considerable errors may be incurred if such an approximation is adopted.
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Published date: 1988
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Local EPrints ID: 461072
URI: http://eprints.soton.ac.uk/id/eprint/461072
PURE UUID: 4e17f2a3-4c83-40a2-9772-ef8acc52981b
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Date deposited: 04 Jul 2022 18:34
Last modified: 04 Jul 2022 18:34
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Author:
David Charles Browne
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