Abstract
This thesis focuses on the growth of high quality III-nitride materials by
MOCVD along both c-direction and non-polar a-direction. High temperature
AlN buffer layer is introduced, which can effectively reduce the dislocation
density of the overlying layer. Stimulated emission at 340nm has been obtained
by such AlN buffer techniques, which mechanism is understood by studying the
strain relaxation in the QW structure with RSM measurements. A non-polar
overgrowth approach has also been established for the growth of non-polar
GaN, leading to an impressive improvement in the crystalline quality.
Meanwhile, optical investigation on c-plane InGaN/GaN MQW nanorod
structures has been performed, demonstrating an significantly enhanced
photoluminescence emission. It has been concluded that the enhancement is
due to the reduction on quantum confined Stark effect caused by strain
relaxation in the MQW structure.
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Publication list
01. Journal articles
1.
Q. Wang, Y. Gong, J. F. Zhang, J. Bai, F. Ranalli, and T. Wang, “Stimulated
emission at 340 nm from AlGaN multiple quantum well grown using high
temperature AlN buffer technologies on sapphire”, Appl. Phys. Lett., 95, 161904
(2009)
2.
Y. Gong, K. Xing, and T. Wang “Influence of high temperature AlN buffer on
optical gain in AlGaN/AlGaN multiple quantum well structure”, Appl. Phys. Lett., 99,
171912 (2011).
3.
K. Xing, Y. Gong, J. Bai, and T. Wang, “InGaN/GaN quantum well structures
with greatly enhanced performance on a-plane GaN grown using self-organized
nano-masks”, Appl. Phys. Lett., 99, 181907 (2011).
4.
Q. Wang, J. Bai, Y. Gong and T. Wang, “Influence of strain relaxation on the
optical properties of InGaN/GaN multiple quantum well nanorods”, J. Phys. D: Appl.
Phys., 44, 395102 (2011).
5.
Y. Gong, K. Xing, and T. Wang, “Optical gain in AlGaN/AlGaN multiple
quantum wells grown on high temperature AlN multiple buffers”, Phys. Status Solidi,
8(7-8): 2056-2058 (2011).
6.
Y. Gong, K. Xing, J. Bai and T. Wang, “Greatly improved crystal quality of
non-polar GaN grown on a-plane GaN nano-rod template obtained using
self-organised nano-masks”, Phys. Status Solidi, 9(3-4):564-567 (2012).
7.
Q. Wang, J. Bai, Y. Gong and T. Wang, “Investigation of the optical properties
of InGaN/GaN nanorods with different indium composition”, Phys. Status Solidi,
9(3-4):620-623 (2012).
8.
J. Bai, Y. Gong, K. Xing, X. Yu and T. Wang, “Efficient reduction of defects in
(11-20) non-polar and (11-22) semi-polar GaN grown on nanorod templates”, Appl.
Phys. Lett., 102, 101906 (2013).
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9.
B. Liu, R. Smith, J. Bai, Y. Gong and T. Wang, “Great emission enhancement
and excitonic recombination dynamics of InGaN/GaN nanorod structures”, Appl.
Phys. Lett., 103, 101108 (2013).
10.
K. Xing, Y. Gong, X. Yu, J, Bai, and T. Wang, “Improved Crystal Quality of
(11-22) Semi-Polar GaN Grown on A Nanorod”, Jpn. Jour. Appl. Phys. 52, 08 (2013)
02. Conference Contributions:
1. Y. P. Gong, J. F. Zhang, Q. Wang, F. Ranalli and T. Wang, “Optical properties of
AlGaN-based materials grown on a new AlN buffer”, UK Nitrides Consortium (UKNC)
Summer Conference, University of Sheffield, UK (2009)
2. Y. P. Gong, J. F. Zhang, Q. Wang, F. Ranalli and T. Wang, “Optical properties of
AlGaN-based materials grown on a new AlN buffer”, International Conference on
Nitride Semiconductors, Jeju, South Korea (2009)
3. Y. P. Gong, J. Zhang, P. Renwick and T. Wang “Growth and characterisation of AlN
with improved crystal quality by using multiple porous AlN buffers on sapphire” UK
Nitride Consortium (UKNC) Winter Conference, Tyndall Institute, Cork, Ireland
(2010)
4. J. Zhang, Y. P. Gong, Q. Wang, P. Renwick and T. Wang “Quantum well thickness
dependent optical anisotropy of spontaneous emission from AlGaN multiple
quantum well structures” UK Nitride Consortium (UKNC) Winter Conference,
Tyndall Institute, Cork, Ireland (2010)
5. Y. P. Gong, K. Xing and T. Wang “Optical gain of strained AlGaN multiple quantum
wells grown on AlN buffers” UK Nitride Consortium (UKNC) Winter Conference,
Manchester, UK (2011)
6. Y. P. Gong, K. Xing, J. Bai and T. Wang “Greatly improved crystal quality of
non-polar GaN grown on a-plane GaN nano-rod template obtained using a
self-organized nano-mask” International Conference on Nitride Semiconductors,
Glasgow, UK (2011)
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7. Y. P. Gong, K. Xing, X. Yu, J. Bai and T. Wang “Improved crystal quality of (11-22)
semi-polar GaN grown on semi-polar nano-rod template” UK Nitride Consortium
(UKNC) Summer Conference, University of Sheffield, UK (2012)
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