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Title: Germanium bipolar transistor design and technology for high frequency applications
Author: Li, Kezheng
ISNI:       0000 0001 2445 9893
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2012
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Germanium is a promising material for future high-performance semiconductor devices due to its superior carrier mobility compared to silicon. Work has been carried out with the aim of investigating the germanium as a semiconductor material for advanced bipolar transistors. A germanium compatible bipolar process has been developed and successfully demonstrated on bulk germanium substrates with a basic bipolar structure. Transistors with good output characteristics were achieved with an Early voltage of 55 V and common emitter current gain of 30. Novel Germanium-on-Sapphire (GeOS) was studied for further development of high-frequency application. GeOS substrates with a high quality single crystal germanium layer of thickness 8 urn were manufactured by direct wafer bonding and subsequent grinding and polishing. The germanium bipolar technology is then migrated to GeOS substrates and transistor output characteristics are reported for the first time. Investigation of poly-Ge emitter technology has been undertaken. A non-selective poly-Ge process at 400 QC has been developed by employing a silicon seed layer. This technology has been characterised by manufacture of a novel diode test structure with an n+ doped poly- Ge contact. A very shallow junction of 62 nm junction was successfully fabricated. Then the production of bipolar transistors on bulk germanium substrates through a self-aligned poly- Ge emitter bipolar process was established. These are the first bipolar transistors of this type to be manufactured and initial tests showed working transistors with a current gain of 50. Silvaco process and device simulation tools have been successfully adapted to model the processing steps in the germanium bipolar process flow and also to predict device performance. The issues that are overcome in this work not only apply to the germanium bipolar device, but also provide very useful information and experimental findings for material scientists and germanium-based process engineering.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available