IR, Visible, and UV Photoluminescence Dependence on the Composition of Quantum Nanocrystals
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ABSTRACT The recent demonstration of PL (Photoluminesc•nce) and EL (Electroluminescence) in porous silicon has been a tremendous advance toward the integration of optoelectronics and Si digital electronics. It has come to be understood that the primary source of luminescence is quantized structures of Si or quantum nanocrvstals (QNCs). We have demonstrated KR,visible and UV photoluminescence from QNCs formed of Si and of Ge in a homogeneous SiO 2 matrix. The nanocrystal dimensions and resulting PL indicate that the active mechanism is 3-dimensional confinement of carriers in the QNCs within the wider bandgap SiO 2 . Raman analysis confirms the presence of QNCs in the -20 to 100 A range. SIMS analysis was used to gauge compositional effects on luminescence wavelength. The QNC matrix concept is immediately extendable to several additional material systems. The stable nature of QNCs embedded within a matrix offer further advances toward the integration of optoelectronics with Si devices.
I. INTRODUCTION Since the recent demonstration by Canham of visible photoluminescence (PL) in porous silicon [1] and numerous other reports describing PL and electroluminescence (EL) in porous silicon [2-6] and in related materials [7-9], a new hope has been generated for development of a fully integrated silicon based opto-electronic material system. Even though the origin of the highly efficient visible PL has not yet been clarified, however, recent studies indicate that the quantum size effect is likely to be the origin of PL from porous silicon. Other, chemical effects, may also stay an active role in some instances. A proper understanding of the origin is very important not only for the physics of the light emission mechanism but also for the
implementaion of the material to commercial opto-electronic devices. We have previously reported that visible PL from the Quantum Nano-Crystals (QNCs) of Si embedded in a Sic 2 591 Mat. Res. Soc. Symp. Proc. Vol. 326. ©1994 Materials Research Society
matrix system. [10] The QNC-matrix system is superior to porous silicon in terms of its mechnical ruggedness, chemical inertness, stability, and life time. Further QNCs are isolated 3 dimensional quantum confinement structures because the QNCs are surrounded by the larger band gap Sic 2 matrix in contrast to porous silicon. The quantum confinement results in efficient radiative recombination, which can lead to efficient luminescent devices. Thus, we believe that the QNC-matrix system will be idel for opto-electronic device integration. The QNC-matrix system has previously been shown to generate EL. [11 ] In this paper, we attempt to tailor the spectrum of the PL emission based on the hypothesis of quantum size effect. One can simplifythe energy band relation of QNCs to a particle in an infinite box potential model. The energy levels for a particle of effective mass m confined to an infinite potential well of dimension txaxt is: Enl,n 2 ,n3 = (n12 + n2 2 + n3 2 )h2 /8mt2 The size (txt) and effective mass are the factors controlling the energy
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