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|Title: ||Synthesis, doping and device applications of II-VI semiconductor nanowires|
|Other Titles: ||II-VI zu ban dao ti na mi xian de he cheng, chan za yi ji qi jian yan jiu|
II-VI 族半導體納米線的合成, 摻雜以及器件研究
|Authors: ||Cao, Yulin ( 曹喻霖)|
|Department: ||Department of Physics and Materials Science|
|Degree: ||Doctor of Philosophy|
|Issue Date: ||2011|
|Publisher: ||City University of Hong Kong|
|Notes: ||CityU Call Number: QC611 .C36 2011|
xvi, 109 leaves : ill. (some col.) 30 cm.
Thesis (Ph.D.)--City University of Hong Kong, 2011.
Includes bibliographical references.
|Abstract: ||ZnTe is an important group II-VI direct band gap semiconductor material with
attractive electronic and optoelectronic properties. Although ZnTe nanowires are very
promising building blocks for nanoscaled optoelectronic devices, several issues have
to be addressed to enable their practical applications. First, how to synthesize ZnTe
nanowires with controlled morphologies at low cost and large scale is an important
challenge to be overcome. Second, controllable and uniform doping in ZnTe
nanowires is a critical prerequisite for semiconducting applications. Last but not least,
how to improve the ZnTe nanowire-based nanodevice performance is predominant in
In the present study, coaxial nanocables with single crystalline ZnTe nanowire
cores and amorphous SiOx shells were synthesized via a simple one-step CVD
approach. Transport characteristics of field-effect transistors (FETs) fabricated from
indvidual ZnTe nanowire cores show typical p-type semiconducting behavior. It was
also revealed that the SiOx shell on the nanocables can act as an effective insulating
layer. Improved electrical properties of p-type ZnTe nanowire FET using HfO2 as the
dielectric layer were also demonstrated.
Moreover, doping of ZnTe nanowires via two approaches, ie., i) ex-situ Ag
doping, ii) in-situ P doping, were successfully demonstrated. For ex-situ Ag doped
ZnTe nanowires, XPS confirmed the existence of Ag in the doped ZnTe nanowires.
The Ag-doped ZnTe nanowires exhibited p-type conductivity about three orders of magnitude higher than that of the undoped ZnTe nanowires. Enhanced p-type
conduction in Ag-doped ZnTe nanowires was attributed to the ion exchange process
on the surface of ZnTe nanowires and diffusion of Ag into ZnTe nanowires.
On the other hand, controlled in-situ P-doping in ZnTe nanowires has been
achieved and shown to enhanced p-type conduction with a resistivity of 2.5 × 103
Ω·cm, a carrier concentration of 5.46 × 1017 cm-3, and a mobility of 4.47 × 10-3 cm-2
V-1 S-1. The enhanced conductivity can be ascribed to the doped P atoms substituting
the Te atoms. The Te P will generate holes at the top of the valence band and thus
enhance the p-type conductivity.
Lastly, ZnTe nanowire photodetectors with good photoconductive sensitivity in
the visible range has been demonstrated. The nanowire photodetector showed the
highest photoconductive gain of 15396 among all reported visible-light
nanostructured photodetectors, including CdS, CdSe, ZnSe, etc. The ZnTe nanowire
photodetector also exhibited a fast response speed of 1.3 s. Finally, the mechanisms of
photoconduction of the photodetectors were discussed.|
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b4086226|
|Appears in Collections:||AP - Doctor of Philosophy |
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