Enhancement effect of photoluminescence in Si nanocrystals by phosphorus implantation
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Enhancement effect of photoluminescence in Si nanocrystals by phosphorus implantation Joonkon Kim, H.J. Woo, H.W. Choi, G.D. Kim and W. Hong Korean Institute of Geoscience and Mineral Resources, 30 Gajung-dong, Yusung-gu, Daejon, 305-350 South Korea ABSTRACT Different from bulk silicon crystal, nano-sized Si crystalline embedded in dielectric medium is known as an efficient light emitting center. In nano-crystalline Si, excitonic electron-hole pairs are considered to be attributed to radiative recombination. But the defects surrounding crystalline nc-Si suppress light emitting, which works as a non-radiative decay path. Hydrogen is usually utilized in order to encapsulate the dangling bonds in the Si:SiO2 interface, dramatically enhancing luminescence yield from nc-Si embedded in dielectric medium. Unfortunately because hydrogen has higher mobility in the matrix, subsequent thermal processes may reduce the enhancement effect. Thus instead of easily reversible hydrogen, phosphorus was introduced by implantation, and was to have the same effect and to be resistive to thermal treatments. Samples were prepared by 400 keV Si implantation with dose of 1 x 1017 Si /cm2 and by multienergy P implantation to make relatively uniform P concentration in the region where implanted Si ions are distributed. Precipitation of crystalline silicon was obtained by annealing at 1100oC for 2 hour in pure Ar environment. Experimental data such as enhancement effect of PL yield, decay time, peak shift for the phosphorus implanted nano-crystalline Si are shown, and the possible mechanisms are discussed. INTRODUCTION Nano crystalline silicon has been paid attention as a Si-based light emitting material [1]. As the size of crystalline Si is small comparable to the Bohr radius, indirect band gap of bulk Si shows quasi-direct property with larger gap energy. Though the luminescence efficiency of nc-Si is higher than bulk c-Si, it is poor compared with usual opto-electronic materials like GaAs etc. While the luminescence mechanism from nc-Si is still under debate, intensity enhancement has been partially successful through the defect passivation by hydrogen. But, since hydrogen is thermally unstable in the substrate, enhancement effect of PL is reversible even with relatively low temperature treatment, e.g., 400oC [2]. Phosphorus addition in the dielectric medium with nc-Si definitely has a PL enhancement effect, but simultaneously quenches PL yield as well. Thus in this study, we will show both the intensity enhancement and quenching effect as a
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function of phosphorus concentration and explain these phenomena as a defect passivation and Auger recombination induced by phosphorus. EXPERIMENTAL Samples were fabricated by ion implantation using the 1.7 MV tandem Pelletron at the Korea Institute of Geoscience and Mineral Resources (KIGAM). Since beam transport efficiency is poor at the low terminal voltage, we compromised implanted Si energy as low as 400 keV in order to have available beam current. The range of Si ion in silica (
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