Optical Photoluminescence due to the Recombination of Donor-Acceptor Pairs in Porous Silicon
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Optical Photoluminescence due to the Recombination of Donor-Acceptor Pairs in Porous Silicon J. P. Zheng1 and X. Wei2 1 Department of Electrical and Computer Engineering, Florida A&M University and Florida State University, Tallahassee, FL 32310, USA 2 The National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA ABSTRACT The temperature dependence of the intensity, peak-wavelength, and bandwidth of photoluminescence (PL) spectra was studied in the porous silicon (PS) sample. To explain the observed temperature dependence, we proposed a model for the origin of the PL in PS. At low temperatures, the photon emission was dominated by the recombination of donor-acceptor pairs with ionization energies of about 4 meV. The donor and the acceptor were spatially separated with a distance of about 3.8 nm, which was about the crystalline size of the PS. Whereas at high temperatures where thermal energy exceeded the ionization energy, the photon emission was mainly from the exciton recombination. INTRODUCTION Since Canham1 demonstrated efficient visible photoluminescence (PL) from porous silicon (PS) at room temperature, much progress has been made in understanding the basic mechanisms of light emission from silicon nanostructures and in producing optoelectronic devices2-8 based on this new material. Numerous models have been put forth to explain the origin of the PL from PS. In a recent review Cullis et al. 9 grouped various proposed models into six categories including crystalline silicon quantum confinement system, hydrogenated amorphous silicon, surface hydrides, various defects in PS, siloxene molecules, and localized electrons and holes at surface states. Among them, the quantum confinement model can account for the most wealth of results presently available. Mauckner et al. 10 proposed the model of quantum-confined exciton and surface state recombination after studying temperature-dependent lifetime and intensity of the PL. Kanemitsu ea al. 11,12 studied temperature-dependent lifetime in PS with different crystalline size and oxidized Si crystallites. They concluded that the hopping- limited recombination process between the crystalline Si and the surface layer of PS contributed to the PL. Koyama et al.13 studied the time- integrated PL spectra and PL decay profile at different emission wavelength. They proposed that the donor-acceptor- like-state recombination is the origin of the PL from PS. Suemoto et al.14 proposed a model that the tunneling and thermally activated escape are mechanisms of nonradiative decay process to explain the experimental results on the temperature dependence of the PL intensity, lifetime, and decay profile in PS. Similar to Suemoto’s model, John15 and Kapoor16 proposed a model involving the competition between activated radiative process and Berthelot-type nonradiative process in order to explain the temperature, pressure, and emission energy dependence of PL. In this paper, we will report our recent experimental results on temperature-dependent PL intensity,
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