Study of III-nitrides heterostructures grown by plasma-assisted molecular beam epitaxy (PAMBE)
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Date
2009
Authors
Chin, Che Woei
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Abstract
In this thesis, the focus is on the studies of the growth of III-nitride
heterostructures for the purpose of developing the new PAMBE system. The studies
include the growth of AlN buffer layer on the substrates for the preparation to grow
III-nitrides epitaxial layers. For exploratory works, the growths were carried out on
Si (111) and sapphire (Al2O3) instead of 6H-SiC which is expensive and commonly
used. To achieve good quality GaN film on Al2O3, nitridation and AlN buffer layer
were applied to overcome the issue of lattice mismatch. An in situ Ga cleaning was
done on Si for removing the SiO2 by formation of Ga2O3 before deposition of the
AlN buffer layer. The thin film surface morphology during the growth was
investigated systematically using reflection high-energy electron diffraction (RHEED)
technique.
In this work, the doping process during epitaxial growth of III-nitrides
heterostructures was investigated. N-type GaN and p-type GaN were successfully
grown on Si (111) and sapphire with carrier concentration as high as 2.31×1018 cm-3
to 4.35×1020 cm-3. III-nitride ternary alloy, InGaN was also successfully grown on Si
(111) in this study. The use of quantum dots (QDs) is more effective in nitride
semiconductors since the zero-dimensional electronic states in the QDs play an
essential role for increasing threshold current in wide bandgap semiconductors.
Therefore, the growth of InGaN quantum dots was also studied in this work. The
InGaN quantum dots with a size around 20-30nm were successfully grown on
sapphire at reduced temperature and without any growth interruption. The electrical,
structural and optical properties of the samples were investigated by using Hall effect
measurements, scanning electron microscopy (SEM), X-ray diffraction (XRD),
photoluminescence (PL) and Raman spectroscopy.
N-type GaN grown on sapphire was selected for the purpose of fabricating
hydrogen gas sensor. The hydrogen detection sensitivity of the device under 0.5%
hydrogen concentration was measured. The sensitivity of the sensor obtained is 4.67
which is higher than that obtained for sensor fabricated with commercial sample.
The results show that the GaN materials system appears to be very promising for use
in hydrogen gas detection.
Description
Master
Keywords
Science Physic , III-nitrides heterostructures , Plasma-assisted molecular beam epitaxy (PAMBE)