Browsing by Author "Gao, R. C."

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InGaN/GaN nanostripe grown on pattern sapphire by metal organic chemical vapor deposition
(2007-01-01)
Ko, T. S.
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Wang, T. C.
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Gao, R. C.
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Lee, Y. J.
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Lu, T. C.
The authors have used metal organic chemical vapor deposition to grow InGaN/GaN multiple quantum well (MQW) nanostripes on trapezoidally patterned c-plane sapphire substrates. Transmission electron microscopy (TEM) images clearly revealed that the MQWs grew not only on the top faces of the trapezoids but also on both lateral side facets along the [0001] direction defined by the selected area electron diffraction pattern. Meanwhile, dislocations that stretched from the interfaces between the GaN and the substrates did not pass through the MQWs in the TEM observation. Microphotoluminescence measurements verified that the luminescence efficiency from a single nanostripe was enhanced by up to fivefold relative to those of regular thin film MQW structures. Observation of the cathodoluminescence identified the areas of light emission and confirmed that enhanced emission occurred from the nanostripes. (c) 2007 American Institute of Physics.
Observations on surface morphologies and dislocations of a-plane GaN grown by metal organic chemical vapor deposition
(2007)
Ko, T. S.
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Wang, T. C.
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Chen, H. G.
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Gao, R. C.
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Huang, G. S.
In this study, we grew non-polar a-plane GaN thin films on r-plane sapphire using a series of growth conditions by metal-organic chemical vapor deposition. The results showed that high temperature and low-pressure conditions benefited two-dimension growth could lead to a fully coalesced a-plane GaN layer with a very smooth surface. The best surface morphology with an excellent mean roughness of 10.5 angstrom was obtained. The different thickness AlN as a nucleation layer and the different delta/beta ratio were also considered. The results revealed that the surface morphology would get worse when the thickness of nucleation layer and delta/beta ratio were away from the values of optimal condition. The observation of transmission electronic microscopy shown the lowest density of threading dislocations was 1.85x10(10) /cm(2). (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Optical characteristics of a-plane InGaN/GaN multiple quantum wells with different well widths
(2007-04-30)
Ko, T. S.
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Lu, T. C.
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Wang, T. C.
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Lo, M. H.
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Chen, J. R.
a-plane InGaN/GaN multiple quantum wells of different widths ranging from 3 to 12 nm were grown on r-plane sapphire by metal organic chemical vapor deposition for investigation. The peak emission intensity of the photoluminescence (PL) reveals a decreasing trend as the well width increases from 3 to 12 nm. Low temperature (9 K) time-resolved PL study shows that the sample with 3-nm-thick wells has a better optical property with a fast exciton decay time of 0.57 ns. The results of cathodoluminescence and micro-PL scanning images for samples of different well widths further verify the more uniform and stronger luminescence intensity distribution observed for the samples of thinner quantum wells, indicating that the important growth parameters for a-plane InGaN/GaN multiple quantum wells could be dominated by the In fluctuation and crystal quality during the epitaxial growth. (c) 2007 American Institute of Physics.
Optical study of a-plane InGaN/GaN multiple quantum wells with different well widths grown by metal-organic chemical vapor deposition
(2008-11-01)
Ko, T. S.
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Lu, T. C.
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Wang, T. C.
;
Chen, J. R.
;
Gao, R. C.
a-plane InGaN/GaN multiple quantum wells of different widths ranging from 3 to 12 nm grown on r-plane sapphire by metal-organic chemical vapor deposition were investigated. The peak emission intensity of the photoluminescence (PL) reveals a decreasing trend as the well width increases from 3 to 12 nm. Low temperature (9 K) time-resolved PL (TRPL) study shows that the sample with 3-nm-thick wells has the best optical property with a fastest exciton decay time of 0.57 ns. The results of cathodoluminescence and micro-PL scanning images for samples of different well widths further verify that the more uniform and stronger luminescence intensity distribution are observed for the samples of thinner quantum wells. In addition, more effective capturing of excitons due to larger localization energy E(loc) and shorter radiative lifetime of localized excitons are observed in thinner well width samples in the temperature dependent TRPL. (c) 2008 American Institute of Physics. [DOI: 10.1063/1.3013435]
Study on optimal growth conditions of a-plane GaN grown on r-plane sapphire by metal-organic chemical vapor deposition
(2007-03-15)
Ko, T. S.
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Wang, T. C.
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Gao, R. C.
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Chen, H. G.
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Huang, G. S.
Non-polar a-plane (1 1 (2) over bar 0) GaN thin films were grown on r-plane (1 (1) over bar 0 2) sapphire substrates by metal-organic chemical vapor deposition. In order to obtain a-plane GaN films with better crystal quality and surface morphology, detailed comparisons between different growth conditions were investigated. The results showed that high-temperature and low-pressure conditions facilitating two-dimensional growth could lead to a fully coalesced a-plane GaN layer with a very smooth surface. The best mean roughness of the surface morphology was 10.5 angstrom. Various thickness values of AlN nucleation layers and the V/III ratios for growth of the a-plane GaN bulk were also studied to determine the best condition for obtaining a smooth surface morphology of the a-plane GaN layer. (c) 2007 Elsevier B.V. All rights reserved.