Browsing by Author "Lee, W. C."

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Correlation between crystal structure and photoluminescence for epitaxial ZnO on Si(111) using a gamma-Al(2)O(3) buffer layer
(2008-03-21)
Liu, W-R
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Li, Y-H
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Hsieh, W. F.
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Hsu, C-H
;
Lee, W. C.
High-quality ZnO epitaxial films were grown by pulsed-laser deposition on Si (1 1 1) substrates with a thin. gamma-Al(2)O(3) buffer layer. The epitaxial. gamma-Al(2)O(3) buffer layer consists of two (1 1 1) oriented domains rotated 60. from each other against the surface normal, which yields the in-plane epitaxial relationship (1 0 0)ZnO
Domain Matching Epitaxial Growth of High-Quality ZnO Film Using a Y(2)O(3) Buffer Layer on Si (111)
(2009-01-01)
Liu, W. -R.
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Li, Y. -H.
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Hsieh, W. F.
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Hsu, C. -H.
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Lee, W. C.
High-quality ZnO epitaxial films have been grown by pulsed-laser deposition on Si (111) substrates using a nanothick high-k oxide Y(2)O(3) buffer layer. Determined by X-ray diffraction and transmission electron microscopy, the epitaxial relationship between ZnO and Y(2)O(3) follows (0001)< 2 (1) over bar(1) over bar0 >(ZnO)parallel to(111)< 10 (1) over bar > Y(2)O(3). ZnO lattice aligns with the hexagonal O sublattice in Y(2)O(3) and the interfacial structure can be well described by domain matching epitaxy with 7 or 8 ZnO {11 (2) over bar0} planes matching 6 or 7 {4 (4) over bar0} planes Of Y(2)O(3) and lead to a significant reduction of residual strain. Superior optical properties were obtained even for ZnO films as thin as 0.21 mu m from photoluminescence results.
Domain Matching Epitaxial Growth of High-Quality ZnO Film Using a Y2O3 Buffer Layer on Si (111)
(2009-01-01)
Liu, W. -R.
;
Li, Y. -H.
;
Hsieh, W. F.
;
Hsu, C. -H.
;
Lee, W. C.
High-quality ZnO epitaxial films have been grown by pulsed-laser deposition on Si (111) substrates using a nanothick high-k oxide Y2O3 buffer layer. Determined by X-ray diffraction and transmission electron microscopy, the epitaxial relationship between ZnO and Y2O3 follows (0001)< 2 (1) over bar(1) over bar0 >(ZnO)parallel to(111)< 10 (1) over bar > Y2O3. ZnO lattice aligns with the hexagonal O sublattice in Y2O3 and the interfacial structure can be well described by domain matching epitaxy with 7 or 8 ZnO {11 (2) over bar0} planes matching 6 or 7 {4 (4) over bar0} planes Of Y2O3 and lead to a significant reduction of residual strain. Superior optical properties were obtained even for ZnO films as thin as 0.21 mu m from photoluminescence results.
Epitaxial stabilization of a monoclinic phase in Y(2)O(3) films on c-plane GaN
(2011-05-15)
Chang, W. H.
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Chang, P.
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Lee, W. C.
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Lai, T. Y.
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Kwo, J.
Nanometer-thick Y(2)O(3) films were grown epitaxially on GaN (0 0 0 1) using molecular beam epitaxy (MBE). The structures of the oxide films were studied in situ by reflection high energy electron diffraction (RHEED) during the growth and ex situ by high resolution X-ray diffraction using synchrotron radiation. At atmospheric pressure. Y(2)O(3) exists in either cubic or hexagonal structure. For the first time, the high-pressure monoclinic phase of Y(2)O(3), stabilized by epitaxy, was prepared and preserved under atmospheric pressure. The electrical characterization carried out on the Y(2)O(3)/GaN metal-oxide-semiconductor (MOS) capacitors showed a leakage current density of similar to 3.3 x 10(-6) A/cm(2) at 1.5 MV/cm, which remained almost the same after 800 degrees C annealing. A dielectric constant of similar to 20 and a hysteresis of similar to 250 mV were deduced from the capacitance-voltage (C-V) curves for the epitaxial monoclinic Y(2)O(3). (C) 2010 Elsevier B.V. All rights reserved.
Epitaxial stabilization of a monoclinic phase in Y2O3 films on c-plane GaN
(2011-05-15)
Chang, W. H.
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Chang, P.
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Lee, W. C.
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Lai, T. Y.
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Kwo, J.
Nanometer-thick Y2O3 films were grown epitaxially on GaN (0 0 0 1) using molecular beam epitaxy (MBE). The structures of the oxide films were studied in situ by reflection high energy electron diffraction (RHEED) during the growth and ex situ by high resolution X-ray diffraction using synchrotron radiation. At atmospheric pressure. Y2O3 exists in either cubic or hexagonal structure. For the first time, the high-pressure monoclinic phase of Y2O3, stabilized by epitaxy, was prepared and preserved under atmospheric pressure. The electrical characterization carried out on the Y2O3/GaN metal-oxide-semiconductor (MOS) capacitors showed a leakage current density of similar to 3.3 x 10(-6) A/cm(2) at 1.5 MV/cm, which remained almost the same after 800 degrees C annealing. A dielectric constant of similar to 20 and a hysteresis of similar to 250 mV were deduced from the capacitance-voltage (C-V) curves for the epitaxial monoclinic Y2O3. (C) 2010 Elsevier B.V. All rights reserved.
Growth and structural characteristics of GaN/AlN/nanothick gamma-Al(2)O(3)/Si (111)
(2008-05-01)
Lee, W. C.
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Lee, Y. J.
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Tung, L. T.
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Wu, S. Y.
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Lee, C. H.
The authors report on the growth of GaN by nitrogen plasma-assisted molecular beam epitaxy (MBE) on a 2 in. Si (111) substrates with a nanothick (similar to 4.8 nm thick) gamma-Al(2)O(3) as a template/buffer. A thin layer of MBE-AlN similar to 40 nm thick was inserted prior to the growth of GaN. High-resolution transmission electron microscopy (HR-TEM) and high-resolution x-ray diffraction studies indicated that both of the nanothick gamma-Al(2)O(3) and AlN are a single crystal. Reflection high-energy electron diffraction, high-resolution x-ray scattering using synchrotron radiation, and cross-sectional HR-TEM measurements indicated an orientation relationship of GaN(0002)parallel to AlN(0002)parallel to gamma-Al(2)O(3)(111)parallel to Si(111) and GaN[10-10]parallel to AlN[10-10]parallel to gamma-Al(2)O(3)[2-1-1]parallel to Si[2-1-1]. A dislocation density of 5x(10(8)-10(9))/cm(2) in the GaN similar to 0.5 mu m thick was determined using cross-sectional TEM images under weak-beam dark-field conditions. (C) 2008 American Vacuum Society.
High-quality nanothick single-crystal Y(2)O(3) films epitaxially grown on Si (111): Growth and structural characteristics
(2008-05-01)
Lee, Y. J.
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Lee, W. C.
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Nieh, C. W.
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Yang, Z. K.
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Kortan, A. R.
High-quality single-crystal nanothick Y(2)O(3) films have been grown epitaxially on Si (111) despite a lattice mismatch of 2.4%. The films were electron beam evaporated from pure compacted powder Y(2)O(3) target in ultrahigh vacuum. Y(2)O(3) 3 nm thick exhibited a bright, sharp, streaky reconstructed (4x4) reflection high energy electron diffraction pattern. Structural studies carried out by x-ray diffraction with synchrotron radiation and high-resolution transmission electron microscopy show that the films have the cubic bixbyite phase with a remarkably uniform thickness and high structural perfection. Two Y(2)O(3) domains of B-type Y(2)O(3) [2 (1) over bar(1) over bar]parallel to Si[11 (2) over bar] and A-type Y(2)O(3) [2 (1) over bar(1) over bar]parallel to Si[2 (1) over bar(1) over bar] coexist in the initial film growth with B type predominating over A type in thicker films as studied using x-ray diffraction. The narrow full width at half maximum of 0.014 degrees in the omega-rocking curve is the characteristic of excellent crystalline films. High-resolution transmission electron microscopy and fast Fourier transform analysis show atomically sharp interface and strain relaxation in thicker films. (C) 2008 American Vacuum Society.
MBE-Enabling technology beyond Si CMOS
(2011-05-15)
Chang, P.
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Lee, W. C.
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Lin, T. D.
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Hsu, C. H.
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Kwo, J.
Achievement of low interfacial densities of states, small equivalent oxide thickness, high kappa values, and thermal stability at high temperatures in the high kappa dielectrics on high carrier mobility semiconductors, the leading candidates for technology beyond Si CMOS, has been made using MBE. This paper reviews our recent advances in meeting the unprecedented demands in materials and physics for the new technology. Moreover, self-aligned inversion-channel InGaAs and Ge MOSFETs using MBE-Ga(2)O(3)(Gd(2)O(3)) as the gate dielectric are compared favorably with those using the gate dielectrics made from other thin film techniques. (C) 2010 Elsevier B.V. All rights reserved.
Structure of HfO2 films epitaxially grown on GaAs(001)
(2006-09-18)
Hsu, C. -H.
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Chang, P.
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Lee, W. C.
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Yang, Z. K.
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Lee, Y. J.
High-quality HfO2 films of technologically important thickness ranging from 1.8 to 17 nm have been grown epitaxially on GaAs (001) by molecular beam epitaxy. Thorough structural and morphological investigations were carried out by x-ray scattering and high-resolution transmission electron microscopy. The films exhibit an atomically sharp interface with the substrate and are of a monoclinic phase with predominant (001)-plane epitaxy between the HfO2 films and GaAs, in spite of a large lattice mismatch of > 8.5%.
The Growth of an Epitaxial ZnO Film on Si(111) with a Gd(2)O(3)(Ga(2)O(3)) Buffer Layer
(2011-07-01)
Lin, B. H.
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Liu, W. R.
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Yang, S.
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Kuo, C. C.
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Hsu, C. -H.
High-quality (0001)-oriented ZnO epitaxial films have been grown by pulsed laser deposition on Si(111) buffered with a nanometer-thick Gd(2)O(3)(Ga(2)O(3)), GGO, layer. The structural characteristics of the ZnO epi-layers were studied by X-ray diffraction and transmission electron microscopy (TEM). The in-plane epitaxial relationship between the wurtzite ZnO, cubic GGO, and cubic Si follows {10 (1) over bar0}(ZNO)parallel to{4 (22) over bar}(Gd2O3)parallel to{(4) over bar 22}(Si) and the ZnO/GGO interface can be described by the domain matching epitaxy. TEM contrast analysis reveals that the major defect structures in the ZnO films are edge-type threading dislocations and intrinsic basal plane stacking faults. All the ZnO epi-films studied are under a tensile biaxial strain, but no cracks were found. Temperature-dependent photoluminescence results show the excellent optical properties of the obtained ZnO layers, and the origins of the spectral features are discussed.
The Growth of an Epitaxial ZnO Film on Si(111) with a Gd2O3(Ga2O3) Buffer Layer
(2011-07-01)
Lin, B. H.
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Liu, W. R.
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Yang, S.
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Kuo, C. C.
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Hsu, C. -H.
High-quality (0001)-oriented ZnO epitaxial films have been grown by pulsed laser deposition on Si(111) buffered with a nanometer-thick Gd2O3(Ga2O3), GGO, layer. The structural characteristics of the ZnO epi-layers were studied by X-ray diffraction and transmission electron microscopy (TEM). The in-plane epitaxial relationship between the wurtzite ZnO, cubic GGO, and cubic Si follows {10 (1) over bar0}(ZNO)parallel to{4 (22) over bar}(Gd2O3)parallel to{(4) over bar 22}(Si) and the ZnO/GGO interface can be described by the domain matching epitaxy. TEM contrast analysis reveals that the major defect structures in the ZnO films are edge-type threading dislocations and intrinsic basal plane stacking faults. All the ZnO epi-films studied are under a tensile biaxial strain, but no cracks were found. Temperature-dependent photoluminescence results show the excellent optical properties of the obtained ZnO layers, and the origins of the spectral features are discussed.
The influence of dislocations on optical and electrical properties of epitaxial ZnO on Si (111) using a gamma-Al2O3 buffer layer
(2012)
Liu, W. -R.
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Lin, B. H.
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Yang, S.
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Kuo, C. C.
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Li, Y. -H.
The structural, optical and electrical properties of the c-plane ZnO epitaxial films grown by pulsed laser deposition on a Si(111) substrate buffered with a thin layer of gamma-Al2O3 were investigated by X-ray diffraction, transmission electron microscopy, photoluminescence (PL) and Hall measurements. Detailed structural investigation showed that the dominant structural defects in the ZnO films are threading dislocations (TDs). Experimental results manifest the edge-and screw-type of TDs influence the optical and electric properties differently; the intensity ratio between the PL yellow-green band to near band edge emission and the carrier concentration are affected mainly by the edge TD, and the FWHM of the near band edge emission is dominantly influenced by the screw TD.
Thickness-dependent lattice relaxation and the associated optical properties of ZnO epitaxial films grown on Si (111)
(2012)
Liu, W. -R.
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Lin, B. H.
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Kuo, C. C.
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Lee, W. C.
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Hong, M.
The evolution of the strain state as a function of layer thickness of (0001) oriented ZnO epitaxial films grown by pulsed-laser deposition on Si (111) substrates with a thin oxide Y2O3 buffer layer was investigated by high resolution X-ray diffraction (XRD). The ZnO layers experience a tensile strain, which gradually diminishes with increasing layer thickness. Regions with a nearly strain-free lattice develop as the layer thickness exceeds a critical value and are correlated with the emergence of the < 11 (2) over bar0 > oriented crack channels. The influence of the biaxial strain to the vibrational and optical properties of the ZnO layers were also studied by micro-Raman, optical reflectance, and photoluminescence. The deformation-potential parameters, a(lambda) and b(lambda), of the E-2(high) phonon mode are determined to be -740.8 +/- 8.4 and -818.5 +/- 14.8 cm(-1), respectively. The excitonic transitions associated with the FXA, FXB, and D degrees X-A emissions and the A-exciton binding energy all show linear dependence on the in-plane strain with a negative slope.
Vertical-cavity and randomly scattered lasing from different thicknesses of epitaxial ZnO films grown on Y2O3-buffered Si (111)
(2013-01-28)
Kuo, C. C.
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Liu, W. -R.
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Lin, B. H.
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Hsieh, W. F.
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Hsu, C. -H.
Two different types of lasing modes, vertical Fabry-Perot cavity and random lasing, were observed in ZnO epi-films of different thicknesses grown on Si (111) substrates. Under optical excitation at room temperature by a frequency tripled Nd:YVO4 laser with wavelength of 355 nm, the lasing thresholds are low due to high crystalline quality of the ZnO epitaxial films, which act as microresonators. For the thick ZnO layer (1,200 nm), its lasing action is originated from the random scattering due to the high density of crack networks developed in the thick ZnO film. However, the low crack density of the thin film (555 nm) fails to provide feedback loops essential for random scattering. Nevertheless, even the lower threshold lasing is achieved by the Fabry-Perot cavity formed by two interfaces of the thin ZnO film. The associated lasing modes of the thin ZnO film can be characterized as the transverse Gaussian modes attributed to the smooth curved surfaces. (C) 2013 Optical Society of America