Browsing by Author "Yao, H. H."

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Effect of growth conditions on the Al composition and quality of AlGaN film
(2007-01-15)
Huang, G. S.
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Yao, H. H.
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Kuo, H. C.
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Wang, S. C.
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光電工程學系
Effects of growth conditions on Al composition and quality of AlxGa1-xN epilayer grown by low-pressure matelorganic vapor phase epitaxy (MOVPE) have been investigated. The dependences of Al composition, growth rate and quality on the NH3 flow rate, TMAl flow rate and growth temperature were studied. The Al composition and quality of AlxGa1-xN film depend not only on the TMAl flow rate, but also on the NH3 flow rate and on the growth temperature. The Al composition of AlxGa1-xN film becomes saturated when the gas-phase composition TMAl/(TMAl + TMGa) increases to 0.4, while quality of AlxGa1-xN film becomes much worse. The Al composition of AlxGa1-xN film increases with increase in the NH3 flow rate. The quality of AlxGa1-xN epilayer is improved when the growth temperature increases. Possible Al incorporation mechanism is discussed. (c) 2006 Elsevier B.V. All rights reserved.
Effects of growth interruption time on InGaN/GaN quantum dots grown by metal organic chemical vapor deposition - art. no. 612102
(2006)
Yao, H. H.
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Huang, G. S.
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Lu, T. C.
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Chen, C. Y.
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Liang, W. D.
Wide-bandgap gallium nitride (GaN) quantum dot (QD) structure is attractive because it is a zero-dimensional (0-D) confinement structure and has many unique physical characteristics. We have successfully grown self-assembled InGaN QDs structure by metal organic chemical vapor deposition. A high quality GaN/sapphire template with a flat surface and the suitable growth condition including low growth temperature and low V/III ratio were used to grow InGaN QDs structure. The density of InGaN QDs is about 4.5 x 10(10) cm(-2) with an average lateral size of 11.5 nm and an average height of 1.6 nm. The effect of the interruption growth for InGaN QDs structure was systematic studied with the growth temperature of 660 degrees C. The surface morphology and optical property was measured by atomic forced microscopy and various temperature PL, respectively. The results indicated that as increasing interruption time from 30s to 120s, QDs area occupied on the surface above the wetting layer increases from 5.2% to 7.2%, and the In composition decreases from 25% to 21%. The results were discussed by considering the influences of ad-atom desorption and diffusion effect between wetting layer and InGaN QDs structure. Our results suggest that the interruption growth during an optimum time can modify the size of InGaN QDs and extend the emission wavelength to short wavelength, and at the same time improve the QD optical quality. Using this technique was feasible for formation of multi layer InGaN QDs structures and applicable for the fabrication of GaN-based light emitting devices.
GaN/AlGaN active regions for terahertz quantum cascade lasers grown by low-pressure metal organic vapor deposition
(2007-01-01)
Huang, G. S.
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Lu, T. C.
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Yao, H. H.
;
Kuo, H. C.
;
Wang, S. C.
The GaN/AlGaN active regions for terahertz (THz) quantum cascade lasers were grown by metal organic chemical vapor deposition (MOCVD). The surface of the sample was characterized by atomic force microscopy (AFM). The structure of this sample was evaluated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD pattern and cross-sectional TEM images showed that a well-controlled quantum cascade GaN/AlGaN layers could be prepared. Optical properties of the active region of a terahertz GaN/AlGaN have been investigated by Fourier transform infrared (FTIR) spectrometer. It was found that the frequency of E-1(LO) phonon decreased in quantum cascade GaN/AlGaN structures. The phonon frequency shift could be attributed to the effect of phonon zone folding. (c) 2006 Elsevier B.V. All rights reserved.