RF-MBE Growth Of III-Nitrides Heterostructures For Light Detecting Applications
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Date
2016-03
Authors
Mohd Yusoff, Mohd Zaki
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
In this research work, GaN p-n homostructures, AlN/GaN heterostructures,
and AlxGa1-xN/Ga heterostructures were successfully grown on silicon (Si) (111)
substrates by plasma-assisted molecular beam epitaxy (MBE) for photodetector
applications. High purity gallium (7N) and aluminum (6N5) were used in the
Knudsen cells and high purity nitrogen (7N) was supplied to 13.56 MHz radio
frequency (RF) source to generate reactive nitrogen species. The nitrogen pressure
and discharge power values were kept constant at 1.5x10-5 Torr and 300 W during
this project, respectively. The surface morphology, structural and optical properties
of all the samples were investigated by using reflection high energy electron
diffraction (RHEED), scanning electron microscopy (SEM), field emission scanning
electron microscopy (FESEM), transmission electron microscopy, atomic force
microscopy (AFM), high-resolution X-ray diffraction (HR-XRD),
photoluminescence (PL), and Raman spectroscopy, respectively. For the growth of
GaN p-n homostructures, Si and magnesium (Mg) were used as n- and p-dopants,
respectively. The RHEED images indicated a good surface morphology of GaN p-n
homostructure layers. According to XRD symmetric rocking curve ω/2ϴ scans of
(0002) plane at room temperature, the full width at half-maximum (FWHM) of GaN
p-n homostructures sample was calculated as 0.34o, indicating a good quality layer of
GaN layer. The effect of the aluminum (Al) flux on the crystal quality of AlN/GaN
heterostructures on Si (111) substrates was investigated. The thickness of 69.94 nm
(AlN top layer) was obtained for good growth conditions giving the comparable FWHM of the XRD rocking curve of 0.46o (27.6 arcmin) when compared with other
samples and previous works. It was found that the AlN/GaN heterostructures grown
under low Al-flux has produced a good structural quality and low compressive strain
value compared to the samples grown under high Al-fluxes. Two samples of low Alcontent
Al0.11Ga0.89N/GaN and Al0.29Ga0.71N/GaN heterostructures were grown on Si
substrates with FWHM of the XRD rocking curve of 0.62o and 0.52o, respectively.
Using the conventional method, the strain values for samplesAl0.11Ga0.89N/GaN and
Al0.29Ga0.71N/GaN heterostructures were calculated as (+) 0.248 % and (-) 0.121 %,
respectively. These values are in good agreement with the studies by other
researchers. The investigation of annealed Pt contact on AlN/GaN heterostructures at
various annealing temperature for 10 min in nitrogen ambient was conducted in this
project. It was found that the Schottky barrier heights (SBHs) and surface of contact
changed with different annealing temperatures. Good results for SBH have been
achieved for sample annealed at 800oC. Meanwhile, the characteristics of annealed
Ni/Ag contact on Al0.11Ga0.89N/GaN heterostructures at various annealing
temperatures for 10 min in oxygen ambient were also studied in this project. The
results revealed that the best SBH value was obtained for the 700oC annealed Ni/Ag
contact on sample. GaN p-n homostructures photodetector and metal-semiconductormetal
(MSM) UV photodetectors of AlN/GaN and AlxGa1-xN/GaN heterostructures
samples have been presented. The fabricated AlN/GaN heterostructures and AlxGa1-
xN/GaN heterostructures based MSM for the UV photodetectors show good
photoconductivity characteristics, suggesting that the samples have good carrier
transport and crystalline properties.
Description
Keywords
AlN/GaN heterostructures