• Korean Journal of Materials Research
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• v.22 no.10
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• pp.539-544
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• 2012

We have grown AlN nanorods and AlN films using plasma-assisted molecular beam epitaxy by changing the Al source flux. Plasma-assisted molecular beam epitaxy of AlN was performed on c-plane $Al_2O_3$ substrates with different levels of aluminum (Al) flux but with the same nitrogen flux. Growth behavior of AlN was strongly affected by Al flux, as determined by in-situ reflection high energy electron diffraction. Prior to the growth, nitridation of the $Al_2O_3$ substrate was performed and a two-dimensionally grown AlN layer was formed by the nitridation process, in which the epitaxial relationship was determined to be [11-20]AlN//[10-10]$Al_2O_3$, and [10-10]AlN//[11-20]$Al_2O_3$. In the growth of AlN films after nitridation, vertically aligned nanorod-structured AlN was grown with a growth rate of $1.6{\mu}m/h$, in which the growth direction was <0001>, for low Al flux. However, with high Al flux, Al droplets with diameters of about $8{\mu}m$ were found, which implies an Al-rich growth environment. With moderate Al flux conditions, epitaxial AlN films were grown. Growth was maintained in two-dimensional or three-dimensional growth mode depending on the Al flux during the growth; however, final growth occurred in three-dimensional growth mode. A lowest root mean square roughness of 0.6 nm (for $2{\mu}m{\times}2{\mu}m$ area) was obtained, which indicates a very flat surface.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.4
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• pp.143-148
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• 2019

We have successfully fabricated high aspect-ratio GaN-based nanowires on Si substrates using molecular beam epitaxy (MBE) system for high-efficiency hydrogen generation of photoelectrochemical water splitting. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) demonstrated that p-GaN:Mg and p-InGaN nanowires were grown vertically on the substrate with high density. Furthermore, it was also confirmed that the emission wavelength of p-InGaN nanowire can be adjusted from 552 nm to 590 nm. Such high-aspect ratio p-InGaN nanowire structure will be a solid foundation for the realization of ultrahigh-efficiency photoelectrochemical water splitting through sunlight.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.310-310
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• 2012

ZnO thin films were grown on porous silicon (PS) by plasma-assisted molecular beam epitaxy (PA-MBE). The optical properties of the ZnO thin films grown on PS were studied using room-temperature, low-temperature, and temperature-dependent photoluminescence (PL). The full width at half maximum (FWHM) of the near-band-edge emission (NBE) from the ZnO thin films was 98 meV, which was much smaller than that of ZnO thin films grown on a Si substrate. This value was even smaller than that of ZnO thin films grown on a sapphire substrate. The Huang-Rhys factor S associated with the free exciton (FX) emission from the ZnO thin films was found to be 0.124. The Eg(0) value obtained from the fitting was 3.37 eV, with ${\alpha}=3.3{\times}10^{-2}eV/K$ and ${\beta}=8.6{\times}10^3K$. The low- and high-temperature activation energies were 9 and 28 meV, respectively. The exciton radiative lifetime of the ZnO thin films showed a non-linear behavior, which was established using a quadratic equation.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.11
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• pp.1005-1009
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• 2006

High quality three-dimensional (3D) heterostructures were constructed by selective area (SA) molecular beam epitaxy (MBE) using a specially patterned GaAs (001) substrate to improve the efficiency of tarrier transport. MBE growth parameters such as substrate temperature, V/III ratio, growth ratio, group V sources (As2, As4) were varied to calibrate the selective area growth conditions and the 3D GaAs-AlGaAs heterostructures were fabricated into the ridge type and the V-groove type. Scanning micro-photoluminescence $({\mu}-PL)$ measurements and the following analysis revealed that the gradually (adiabatically) coupled 1D-2DEG (electron gas) field effect transistor (FET) system was successfully realized. These 3D-heterostructures are expected to be useful for the realization of high-performance mesoscopic electronic devices and circuits since it makes it possible to form direct ohmic contact onto the (quasi) 1D electron channel.

• Korean Journal of Materials Research
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• v.12 no.3
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• pp.195-199
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• 2002

Planar Hall effect of ferromagnetic GaMnAs thin films was investigated for the first time. The films were grown in an optimized growth condition via molecular beam epitaxy at low temperatures. For the optimization of the growth conditions, we used reflection high-energy electron diffraction, electrical conductivity, double crystal x-ray diffraction, and superconducting quantum interference device measurements techniques. We observed that the difference between the longitudinal resistance and the transverse resistance matches the planar Hall resistance. The ratio of the planar Hall resistance at saturation magnetic field to that at zero reached above 500%.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.10
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• pp.828-833
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• 2000

Growth characteristics and microstructure of AIN thin films grown by plasma assisted molecular beam epitaxy on Si substrates have been investigated. Growing temperature and substrate orientation were chosen as major variables of the experiment. Reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy/diffraction (TEM/TED) techniques were employed to characterize the micorstructure of the films. On Si(100) substrates, AlN thin films were grown along the hexagonal c-axis preferred orientation at temperature range 850-90$0^{\circ}C$. However on Si(111), the AlN films were epitaxially grown with directional coherency in AlN(0001)/Si(111), AlN(1100)/Si(110), and AlN(1120)/Si(112) at 85$0^{\circ}C$ and the epitaxial coherencry seemed to be slightly distorted with increasing temperature. The microstructure of AlN thin films on Si(111) substrates showed that the films include a lot of crystal defects and there exist micro-gaps among the columns.

• Korean Journal of Materials Research
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• v.12 no.5
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• pp.387-390
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• 2002

A new approach of using double buffer layers of AlN and GaN for growth of GaN films on Si has been undertaken via molecular beam epitaxy using ammonia. The first buffers layer of AlN was grown using $N_2$plasma and the second of GaN was grown using ammonia. The surface roughness of the grown films was investigated by atomic force microscope and was compared with the normally grown films on sapphire. Double crystal x-ray rocking curve and low temperature photoluminescence techniques were employed for structural and optical properties examination. Donor bound exciton peak at 3.481 eV with full width half maximum of 41 meV was observed at 13K.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.111-114
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• 2000

Growth characteristics and microstructure of AlN thin films grown by plasma assisted molecular beam epitaxy on Si substrates have been investigated. Growing temperature and substrate orientation were chosen as major variables of the experiment. Reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy/diffraction (TEM/TED) techniques were employed to characterize the microstructure of the films. On Si(100) substrates, AlN thin films were grown along the hexagonal c-axis preferred orientation at temperature range 850-90$0^{\circ}C$. However on Si(111), the AlN films were epitaxially grown with directional coherency in AlN(0001)/Si(111), AlN(1100)/Si(110), and AlN(1120)/Si(112) at 85$0^{\circ}C$ and the epitaxial coherencry seemed to be slightly distorted with increasing temperature. The microstructure of AlN thin films on Si(111) substrates showed that the films include a lot of crystal defects and there exist micro-gaps among the columns.

• Journal of the Korean Vacuum Society
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• v.12 no.4
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• pp.251-256
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• 2003

Indium aluminum arsenide(InAlAs) was grown by molecular beam epitaxy on (001) indium phosphide (InP) substrate and the effects of growth temperature on the properties of epitaxial layers were studied. In the temperature range of 370-$400 ^{\circ}C$, we observed that the surface morphology, optical quality and structural quality of InAlAs epilayers were improved as growth temperature increased. However, the InAlAs epilavers grown at $430 ^{\circ}C$ have the bad surface morphology and show the same trends as structural and epical quality. As a result of these measurements, it is suggested that the InAlAs epilayers of very good properties can be grown at $400 ^{\circ}C$.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.202.1-202.1
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• 2013

ZnO nanostructure was fabricated on a Si substrate using two-step growth. The seed layer was grown on the Si substrate by a sol-gel spin-coating. In the first step, ZnO nanorods were grown by a hydrothermal method at $140^{\circ}C$ for 5 min. In the second step, a ZnO thin film was grown on the ZnO nanorods by spin-coating. After growth, these films were annealed at $800^{\circ}C$ for 10 min. Electrical and optical properties of ZnO nanostructures have modified by plasma-assisted molecular beam epitaxy (PA-MBE) regrowth. The carrier concentration and resistivity increased by PA-MBE regrowth. In the photoluminescence, the full width at half maximum and intensity were decreased and increased, respectively, by PA-MBE regrowth.