Intense Photoluminescence and Photoluminescence Enhancement upon Ultraviolet Irradiation in HYydrogenated Nanocrystallin
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Intense Photoluminescence and Photoluminescence Enhancement upon Ultraviolet Irradiation in HYydrogenated Nanocrystalline Silicon Carbide M.B.Yu, Rusli and S.F.Yoon School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Republic of Singapore S.J. Xu Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, China K.Chew, J. Cui, J. Ahn and Q. Zhang School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Republic of Singapore ABSTRACT Hydrogenated nanocrystalline silicon carbide (nc-SiC:H) films were deposited in an electron cyclotron resonance chemical vapor deposition (ECR-CVD) system using silane (SiH4) and methane (CH4) as source gases. It was discovered that under the deposition conditions of strong hydrogen dilution and high microwave power, nanocrystalline grains embedded in an amorphous matrix can be obtained, as confirmed by TEM study. Steady state and time-resolved photoluminescence (PL) from these films were investigated. The films exhibit intense visible PL at room temperature under laser excitation. The PL emission peaks at 2.64 eV, which is higher in energy compared to the bandgap of cubic SiC. Temporal evolution of the emission peak exhibits a double-exponential decay. Two distinct decay times of 179 ps and 2.88 ns were identified, which are at least 2 orders of magnitude faster than that of bound excition transitions in bulk 3CSiC at low temperature. It was found that upon ultraviolet irradiation using an Ar+ laser (351nm) the PL intensity of the films was enhanced. After 20 minutes irradiation, the PL intensity increased by about three times. This result suggests that the UV light may lead to modification of nonradiative recombination centers in the films. These nc-SiC:H films are promising for application in large area flat panel displays and in optoelectronic storage technology. INTRODUCTION Nanocrystalline semiconductor materials have attracted much attention due to their potential application in novel optical and electro-optical devices1-2. In recent years, many techniques, such as sputtering, laser-chemical vapor deposition, ion implantation, and plasma enhanced CVD, have been adopted for the preparation of films consisting of nanocrystalline Si embedded in a matrix of silicon nitride or oxide. These films have been shown to exhibit visible photoluminescence (PL), attributed to quantum size effects in the Si nanocrystallites3-6. Apart from nanocrystalline Si, fabrication of other similar films consisting of nanocrystallites of C7, Ge8, GaAs9, GaN10 and diamond11 embedded in silicon oxide or other matrixes have also been reported. Crystalline SiC, being a wide band gap semiconductor, exhibits weak blue PL at low temperature, and blue light emitting diodes (LED) based on this material have been demonstrated12. However, due to its indirect band gap characteristic, the intensity of the LED is very low, with a quantum efficiency of only about 10-4 13. To improve
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