Browsing by Author "Susanto, Iwan"

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Effects of N/Ga flux ratio on GaN films grown on 4H-SiC substrate with 4 degrees miscutting orientation by plasma-assisted molecular beam epitaxy
(2017-07-05)
Susanto, Iwan
;
Tsou, Tsung-Han
;
Yang, Zu-Po
;
Lee, Chao-Yu
;
Li, Hui
High-quality GaN films grown on 4H-SiC (0001) substrate with 4 of miscutting orientation have been done by plasma-assisted molecular beam epitaxy with different N/Ga flux ratio. The effect of N/Ga flux ratio on the surface morphology, chemical composition, structural and optical properties was systematically investigated. The observations of in-situ reflective high-energy electron diffraction demonstrated the special surface of SiC substrate and GaN growth transition from two-to three-dimension depending on N/Ga flux ratio. In the Ga-rich condition for epitaxy, Ga droplets formed and the root mean square value of surface roughness increased by the characterizations of scanning electron microscopy and atomic force microscopy which also related to the formation of the pits on the surface due to the accumulation of excess Ga on the surface. The better growth parameter of GaN films in the work is N/Ga flux ratio of 28 at substrate temperature 700 degrees C. Its surface oxide and charge-compensated surface state associated with defects are minimized from the surface composition analysis of X-ray photoelectron spectroscopy. In the structural characterization of high-resolution X-ray diffraction, the value of full width at half maximum and density of threading dislocation are lower to prove the high-quality structure of GaN film grown at N/Ga flux ratio of 28. Finally, the photoluminescence analysis performed the narrow near-band-edge peak and yellow band, corresponding to the better quality of GaN films. In this report, high-quality GaN films on 4H-SiC (0001) with 4 of miscutting orientation have been demonstrated by the reduction of defect states via the different N/Ga flux ratio. N/Ga flux ratio not only influences the growth mechanism and surface morphology, but also the surface chemical composition, crystal quality and optical properties of GaN compound semiconductors. (C) 2017 Elsevier B.V. All rights reserved.
The influence of 2D MoS2 layers on the growth of GaN films by plasma-assisted molecular beam epitaxy
(2019-12-01)
Susanto, Iwan
;
Tsai, Chi-Yu
;
Fachruddin
;
Rahmiati, Tia
;
Ho, Yen-Ten
In the report, the growth of GaN films on the two-dimension molybdenum disulfide (2D MoS2) and c-sapphire via plasma-assisted molecular beam epitaxy (MBE) was investigated. Two kinds of MoS2 layers were prepared by pulsed laser deposition (PLD) and chemical vapor deposition (CVD) techniques. Three different surface conditions were designed for the growth of GaN films. GaN thin films in the form of polycrystalline were successfully grown on the surface of MoS2 layers. From the surface analysis, CVD technique provided an amorphous and rougher MoS2 surface for the MBE growth. On the contrary, PLD supplied a better in-plane and smoother surface for GaN growth which included more stability of surface chemical composition, higher crystallinity and better near-band-edge emission property. To compare with the growth on c-Sapphire, however, the van der Waals expitaxial growth of single-crystalline GaN films on sp(2) bonded 2D MoS2 is still a challenge. The growth of GaN films on sp(3) bonded c-sapphire still performed the best results in the report. In summary, we demonstrate better growth of GaN thin films on 2D MoS2 surface provided by PLD. The hetetrostructure of 3D GaN on 2D MoS2 semiconductors could be useful in the future applications of electronic and optoelectronic devices.