Browsing by Author "Chen, Chiang-Yao"

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Dislocation reduction in GaN film using Ga-lean GaN buffer layer and migration enhanced epitaxy
(2011-07-29)
Wong, Yuen-Yee
;
Chang, Edward Yi
;
Wu, Yue-Han
;
Hudait, Mantu K.
;
Yang, Tsung-Hsi
A GaN buffer layer grown under Ga-lean conditions by plasma-assisted molecular beam epitaxy (PAMBE) was used to reduce the dislocation density in a GaN film grown on a sapphire substrate. The Ga-lean buffer, with inclined trench walls on its surface, provided an effective way to bend the propagation direction of dislocations, and it reduced the dislocation density through recombination and annihilation processes. As a result, the edge dislocation density in the GaN film was reduced by approximately two orders of magnitude to 2 x 10(8) cm(-2). The rough surface of the Ga-lean buffer was recovered using migration enhanced epitaxy (MEE), a process of alternating deposition cycle of Ga atoms and N(2) radicals, during the PAMBE growth. By combining these two methods, a GaN film with high-crystalline-quality and atomically-flat surface can be achieved by PAMBE on a lattice mismatch substrate. (C) 2011 Elsevier B.V. All rights reserved.
Epitaxial Overgrowth of Gallium Nitride Nano-Rods on Silicon (111) Substrates by RF-Plasma-Assisted Molecular Beam Epitaxy
(2010)
Ku, Jui-Tai
;
Yang, Tsung-Hsi
;
Chang, Jet-Rung
;
Wong, Yuen-Yee
;
Chou, Wu-Ching
Strain-free gallium nitride (GaN) overgrowth on GaN nano-rods is realized by RF-plasma assisted molecular beam epitaxy (RF-MBE) on silicon (Si) substrate. The strain-free condition was identified by the strong free A exciton (FX(A)) photoluminescence (PL) peak at 3.478 eV and the E(2) high phonon Raman shift of 567 cm(-1). It is clearly demonstrated that the critical diameter of GaN nano-rods is around 80nm for the overgrowth of strain-free GaN. The blue-shift of PL peak energy and phonon Raman energy with decreasing the diameter of nano-rod result from the strain relaxation of overgrowth GaN. (C) 2010 The Japan Society of Applied Physics
Highly Efficient and Bright LEDs Overgrown on GaN Nanopillar Substrates
(2011-07-01)
Chiu, Ching-Hsueh
;
Tu, Po-Min
;
Lin, Chien-Chung
;
Lin, Da-Wei
;
Li, Zhen-Yu
We presented a study of high-performance GaN-based light emitting diodes (LEDs) using a GaN nanopillars (NPs) structure grown on sapphire substrate by integrating RF-plasma molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). Nanoscale air voids were clearly observed at the interface between GaN NPs and the overgrown GaN layer by cross-sectional scanning electron microscopy. It can increase the light-extraction efficiency due to additional light scattering. The transmission electron microscopy images suggest the air voids between GaN NPs introduced during nanoscale epitaxial lateral overgrowth of GaN can suppress the threading dislocation density. Moreover, Raman spectrum demonstrated that the strain of the GaN layer grown on GaN NPs was effectively eliminated, resulting in the reduction of quantum-confined Stark effect in InGaN/GaN quantum wells. Consequently, the LEDs fabricated on the GaN NPs template exhibit smaller electroluminescent peak wavelength blue shift and great enhancement of the light output (70% at 20 mA) compared with the conventional LEDs.