|dc.description||Cataloged from PDF version of article.||en_US
|dc.description.abstract||GaN-based bipolar transistors are good candidates for applications in RF power
amplifiers. In contrast to more common AlGaN/GaN high electron mobility transistors
(HEMTs), GaN based bipolar transistors have not drawn much attention
because of the difficulties in good p-type material and ohmic contact. Most of
the problems associated with p-type quality and contact come from growth and
etch damage during fabrication.
In this work, a low damage etching technique with an undercut profile was
developed to solve the problems associated with p-type ohmic contact quality
and to realize the self-aligned GaN bipolar transistor fabrication. The etching
process consists of bias-assisted photoenhanced electrochemical oxidation of GaN
in deionized water (BPECO/DI) and its subsequent etching in diluted acid solution.
By this technique, we demonstrated good Schottky contacts on samples
etched more than 100 nm and p/n doping selective etching was shown. Furthermore
the most critical point for self-aligned fabrication is undercut profile and it was also obtained by BPECO/DI etching. Hence this technique is ideal for
fabrication of self-aligned bipolar transistors.
There are some problems during fabrication of self-aligned bipolar transistor.
First, due to the impossibility of activation annealing after emitter etch,
activation annealing had to be done at the beginning where emitter layer is on
the base and this was a problem for Mg activation. More importantly, there
were still uncertainties with BPECO/DI etching like roughening up the etched
surface, low etch rate for npn structures and disturbing the material uniformity
near the surface.
In this work, it was shown that BPECO/DI etching is a very efficient tool
that provided low damage etching of GaN and enabled the self aligned RF bipolar
transistor structures. It was found that self aligned base-emitter junctions were
successfully formed and the BPECO/DI etching was almost stopped at top of the
base layer. Self-aligned bipolar transistors were fabricated and their base-emitter
and base-collector junctions were measured. The results obtained in this work
demonstrated that BPECO/DI etching can bring solutions to the lack of low
damage etching and the impossibility of self-aligned base contact in fabrication
of today’s GaN based bipolar transistors.||en_US
|dc.format.extent||xi, 55 leaves, illustrations, graphics||en_US
|dc.subject||Photo-enhanced electrochemical etching||en_US
|dc.subject||Low damage etching||en_US
|dc.subject.lcc||TK7871.15.G33 A58 2006||en_US
|dc.title||Investigation of Bias-assisted photoenhanced electrochemical etching for fabrication of self-alihned gallium nitride based bipolar transistors||en_US
|dc.department||Department of Electrical and Electronics Engineering||en_US