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Localized Deformation and Fracture Behaviors in InP Single Crystals by Indentation
(2018-12-01)
Chiu, Yi-Jui
;
Jian, Sheng-Rui
;
Liu, Ti-Ju
;
Phuoc Huu Le
;
Juang, Jenh-Yih
The indentation-induced deformation mechanisms in InP(100) single crystals were investigated by using nanoindentation and cross-sectional transmission electron microscopy (XTEM) techniques. The results indicated that there were multiple pop-in events randomly distributed in the loading curves, which were conceived to arise primarily from the dislocation nucleation and propagation activities. An energetic estimation on the number of nanoindentation-induced dislocations associated with pop-in effects is discussed. Furthermore, the fracture patterns were performed by Vickers indentation. The fracture toughness and the fracture energy of InP(100) single crystals were calculated to be around 1.2 MPam(1/2) and 14.1 J/m(2), respectively.
Enhancing the Emission Efficiency of In0.2Ga0.8N/GaN MQW Blue LED by Using Appropriately Misoriented Sapphire Substrates
(2009-01-01)
Li, Zhen-Yu
;
Uen, Wu-Yih
;
Lo, Ming-Hua
;
Chiu, Ching-Hua
;
Lin, Po-Chun
In this paper, we report the fabrication of an In0.2Ga0.8N/GaN multiple-quantum-well (MQW) structure on vicinal sapphire substrates with a very small offset angle of 0-1 degrees by low-pressure metallorganic chemical vapor deposition. Our study demonstrates that the quality of the In0.2Ga0.8N/GaN MQW structure is very sensitive to the offset angle of the vicinal substrate. High-resolution X-ray diffraction analyses demonstrated high-order satellite peaks and clear fringes between them for all MQW structures fabricated, from which the interface roughness (IRN) was estimated. The IRN of the In0.2Ga0.8N/GaN MQW structure fabricated on 0.2 degrees off sapphire substrate was determined as 1.36% of the quantum well layer period. Besides, reciprocal lattice mapping was employed to examine the strain status of the MQW. The lattice relaxation of the same specimen mentioned above was estimated to be 7.4x10(-5). It is therefore manifested that an In0.2Ga0.8N/GaN MQW structure with abrupt interfaces and good layer periodicity was grown. From it, a shortest radiative lifetime of 14.2 ns and a lowest fluctuation of 5.6 meV in the emission energy of micro-photoluminescence mapping were achieved. In addition, superior material qualities of the whole film fabricated on 0.2 degrees off substrate were recognized by cross-sectional transmission electron microscopy. Based on the results mentioned above, a high-quality In0.2Ga0.8N/GaN MQW blue light, emitting diode (LED) has been fabricated on 0.2 degrees off substrate, which demonstrated a strong room-temperature electroluminescence emission at the wavelength of 465 nm and with the full width at half maximum of only 19 nm. The same device also showed an output power of 13.4 mW and an external quantum efficiency of 19.2%. Both these characteristics are improved drastically compared with the devices fabricated on the substrates with other offset angles. Conclusively, the use of an appropriately misoriented sapphire substrate is suggested to be effective for elevating the emission efficiency of In0.2Ga0.8N/GaN MQW blue LED fabricated thereon.
Phase transition behaviors of Mo- and nitrogen-doped Ge2Sb2Te5 thin films investigated by in situ electrical measurements
(2009-08-01)
Huang, Yu-Jen
;
Chen, Yen-Chou
;
Hsieh, Tsung-Eong
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Phase-change behaviors of Ge2Sb2Te5 (GST) thin films doped with molybdenum (Mo) or nitrogen (N) were investigated by utilizing in situ electrical property measurement, x-ray diffraction (XRD), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy. It was found that the Mo doping mainly reduces the resistivity level of amorphous GST while the N-doping raises both the resistivity levels of amorphous and crystalline GSTs. XRD and TEM analyses revealed that the element doping stabilizes the amorphous state of GST and suppresses the grain growth in GST films. This resulted in the increase in recrystallization temperature (T-m) and activation energy (E-a) of amorphous-to-crystalline phase transition in GST layers, as revealed by the calculation in terms of Kissinger's theory. The results of data fitting into various percolation models and Johnson-Mehl-Avrami analysis indicated the heterogeneous feature of phase transition process in GST layers that the nucleation first occurs at the atmosphere/sample interface and the recrystallization front advances into the interior of sample in a layer-by-layer manner along the direction of surface normal.
Structural and Stress Properties of A1GaN Epilayers Grown on A1N-Nanopatterned Sapphire Templates by Hydride Vapor Phase Epitaxy
(2018-09-01)
Tasi, Chi-Tsung
;
Wang, Wei-Kai
;
Ou, Sin-Liang
;
Huang, Shih-Yung
;
Horng, Ray-Hua
In this paper, we report the epitaxial growth and material characteristics of AlGaN (Al mole fraction of 10%) on an AlN/nanopatterned sapphire substrate (NPSS) template by hydride vapor phase epitaxy (HYPE). The crystalline quality, surface morphology, microstructure, and stress state of the AlGaN/AlN/NPSS epilayers were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The results indicate that the crystal quality of the A1GaN film could be improved when grown on the A1N/NPSS template. The screw threading dislocation (TD) density was reduced to 1.4 x 10(9) cm(-2) for the AlGaN epilayer grown on the A1N/NPSS template, which was lower than that of the sample grown on a flat c-plane sapphire substrate (6.3 x 10(9) cm(-2)). As examined by XRD measurements, the biaxial tensile stress of the AlGaN film was significantly reduced from 1,187 MPa (on A1N/NPSS) to 38.41 MPa (on flat c-plane sapphire). In particular, an increase of the Al content in the overgrown AlGaN layer was confirmed by the TEM observation. This could be due to the relaxation of the in-plane stress through the AlGaN and AlN/NPSS template interface.
Luminescence mechanisms of silicon-rich nitride films fabricated by atmospheric pressure chemical vapor deposition in N-2 and H-2 atmospheres
(2009-03-01)
Lin, Chia-Hung
;
Uen, Wu-Yih
;
Lan, Shan-Ming
;
Huang, Yen-Chin
;
Liao, Sen-Mao
This work examines possible luminescence mechanisms of silicon-rich nitride (SRN) films that were fabricated by atmospheric pressure chemical vapor deposition (APCVD). Under an ambient gas of either H-2 or N-2, two SRN films were deposited using the same precursors of Si and N. While photoluminescence (PL) measurements of both as-deposited specimens revealed an intense luminescence band (1.8-3.8 eV), which was observable by the naked eye, a detailed examination of the high energy band of the PL spectra over 2.8 eV yielded different results for those samples that were fabricated in different ambiences. To determine the reason for these differences, Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy were conducted, suggesting unique chemical bonds and elemental ratio of nitrogen to silicon in SRN films. Further analysis involving plan-view high-resolution transmission electron microscopic observations of SRN films demonstrated the embedding of Si quantum dots (Si QDs), but with some differences depending on the deposition environment. Analyses of the results obtained suggest that the emission from SRN films that were deposited by APCVD is not only dominated by the quantum confinement effect of Si QDs, but also subordinately affected by the surface states around these Si QDs.
The microstructure of As precipitates in Si delta-doped GaAs grown by low-temperature molecular beam epitaxy
(1997-11-01)
Hsieh, LZ
;
Huang, JH
;
Su, ZA
;
Guo, XJ
;
Shih, HC
The structure relationship of the As precipitates found in post-annealed Si delta-doped GaAs layers grown by low-temperature molecular beam epitaxy is elucidated by transmission electron microscopy (TEM). There are six extra spots around the diffraction pattern of GaAs for a sample annealed at 700 degrees C. The As precipitates and GaAs matrix are found to be semicoherent with the hexagonal [-1-21](As) parallel to the cubic [110](GaAs). Because of the different lattice constants and Bravias lattices between GaAs and As precipitates, these extra spots are formed by double-diffraction effects. The high-resolution TEM images show two types of Moire fringes. One is the parallel Moire pattern and the other is the rotation Moire pattern. The relative positions of the extra spots in the diffraction pattern correspond to the orientation and spacing of Moire fringes.
High Density Ni Nanocrystals Formed by Coevaporating Ni and SiO2 Pellets for the Nonvolatile Memory Device Application
(2010-01-01)
Hu, Chih-Wei
;
Chang, Ting-Chang
;
Tu, Chun-Hao
;
Huang, Yu-Hao
;
Lin, Chao-Cheng
We propose a method to fabricate a Ni nanocrystal structure by simultaneously coevaporating Ni and SiO2 pellets. An 800 degrees C rapid thermal annealing was used to enhance the Ni nanocrystals to aggregate. Transmission electron microscopy indicates that the formed Ni nanocrystals show a high density distribution of about 4.5x10(12) cm(-2). Then, the memory device using the Ni nanocrystals as charge-trapping centers was fabricated. The Ni nanocrystal memory device has an obvious memory window under capacitance-voltage measurement. X-ray photoelectron spectroscopy confirms the memory effect results from the Ni nanocrystals embedded in the SiO2 dielectric layer. Moreover, related reliability characteristics have been extracted.
High extraction efficiency GaN-based light-emitting diodes on embedded SiO2 nanorod array and nanoscale patterned sapphire substrate
(2010-06-28)
Huang, Hung-Wen
;
Huang, Jhi-Kai
;
Kuo, Shou-Yi
;
Lee, Kang-Yuan
;
Kuo, Hao-Chung
In this paper, GaN-based LEDs with a nanoscale patterned sapphire substrate (NPSS) and a SiO2 photonic quasicrystal (PQC) structure on an n-GaN layer using nanoimprint lithography are fabricated and investigated. The light output power of LED with a NPSS and a SiO2 PQC structure on an n-GaN layer was 48% greater than that of conventional LED. Strong enhancement in output power is attributed to better epitaxial quality and higher reflectance resulted from NPSS and PQC structures. Transmission electron microscopy images reveal that threading dislocations are blocked or bended in the vicinities of NPSS layer. These results provide promising potential to increase output power for commercial light emitting devices. (C) 2010 American Institute of Physics. [doi:10.1063/1.3456385]
Epitaxial single-crystal of GaSe epilayers grown on a c-sapphire substrate by molecular beam epitaxy
(2015-10-01)
Wu, Chia-Hsin
;
Yang, Chu-Shou
;
Wang, Yen-Chi
;
Huang, Hsi-Jung
;
Ho, Yen-Teng
In this study, hetero-epitaxy of GaSe epilayers on a c-sapphire substrate achieved using molecular beam epitaxy was demonstrated. The GaSe epitaxial growth was monitored using in situ reflection high-energy electron diffraction (RHEED). Streak RHEED patterns showed a flat and highly crystalline situation. Furthermore, two RHEED patterns were observed after 15min of growth, and they were correlated with the m-axis and a-axis of hexagonal GaSe. The single crystal of GaSe was verified using X-ray diffraction and high-resolution cross-section transmission electron microscopy. The full width at half-maximum of (0002) in the XRD rocking-curve spectrum of GaSe epilayer is obtain around 207arcsec, which is the smallest value observed to date. The epitaxial growth of GaSe demonstrated the feasibility of growing large-area epilayers.
Formation of omega and Ti2Ni phases in a residual Ti-Ni-Ti multilayer between stainless steel and zirconia after bonding at 1173K
(2014-10-03)
Wei, Shen-Hung
;
Lin, Chien-Cheng
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Stainless steel (316L) and 8mol pct Y2O3-stabilized zirconia (8Y-ZrO2) were bonded using a Ti-Ni-Ti multilayer at 1173K (900 degrees C) for 1h. Cross-sectional transmission electron microscopy specimens were prepared by an innovative focused ion beam plus lift-out technique. In addition to acicular alpha-Ti, the dissolution of Fe, Cr, and Ni diffusing outwards from 316L into beta-Ti led to the precipitation of the omega (omega) phase with different variants in the residual Ti foil between 316L and Ni. The omega-phase was not found in the residual Ti foil between Ni and 8Y-ZrO2, while Ti2Ni precipitates were precipitated in some alpha-Ti grains owing to the exclusion of Ni from the beta-Ti.

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