Browsing by Author "Hsiao, Y. L."

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Nonpolar a-plane GaN grown on r-plane sapphire using multilayer AlN buffer by metalorganic chemical vapor deposition
(2011-01-15)
Chiang, C. H.
;
Chen, K. M.
;
Wu, Y. H.
;
Yeh, Y. S.
;
Lee, W. I.
Mirror-like and pit-free non-polar a-plane (11-20) GaN films are grown on r-plane (1-102) sapphire substrates using metalorganic chemical vapor deposition (MOCVD) with multilayer high-low-high temperature AlN buffer layers. The buffer layer structure and film quality are essential to the growth of a flat, crack-free and pit-free a-plane GaN film. The multilayer AlN buffer structure includes a thin low-temperature- deposited AlN (LT-AlN) layer inserted into the high-temperature-deposited AlN (HT-AlN) layer. The results demonstrate that the multilayer AlN buffer structure can improve the surface morphology of the upper a-plane GaN film. The grown multilayer AlN buffer structure reduced the tensile stress on the AlN buffer layers and increased the compressive stress on the a-plane GaN film. The multilayer AlN buffer structure markedly improves the surface morphology of the a-plane GaN film, as revealed by scanning electron microscopy. The effects of various growth V/III ratios was investigated to obtain a-plane GaN films with better surface morphology. The mean roughness of the surface was 1.02 nm, as revealed by atomic force microscopy. Accordingly, the multilayer AlN buffer structure improves the surface morphology and facilitates the complete coalescence of the a-plane GaN layer. (C) 2010 Elsevier B.V. All rights reserved.
Photoluminescence and Raman studies of GaN films grown by MOCVD
(2009)
Luong Tien Tung
;
Lin, K. L.
;
Chang, E. Y.
;
Huang, W. C.
;
Hsiao, Y. L.
The photoluminescence (PL) of high quality GaN epitaxial layer grown by MOCVD was investigated for various excitation power and temperatures from 8.3 to 300K. The PL at 8.3 K and with relatively low excitation power of GaN film grown on c-plane sapphire by using MOCVD shows clearly free-exciton A, B and exciton A bound to neutral donors (D degrees X) at 3.502 eV, 3.509 eV, and 3.496 eV, respectively. The full width at half maximum (FWHM) and binding energy of exciton A of the high quality GaN film were evaluated as small as 3.7 meV and 27.9 +/- 0.5 meV, respectively. In addition, PL and Raman scattering of GaN films grown on r-plane sapphire and (111) Si substrates by using MOCVD were examined. The residual stress effect was detected in all films.