Thermal quenching behavior of Er-doped silicon-rich SiO2 prepared by ion implantation
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Erbium and silicon were dual implanted into thermally grown SiO2 film on Si (110) substrates, followed by thermal treatment at 700–1200 °C for 30 min. The microstructure was studied by transmission electron microscope and x-ray diffraction. When the implanted films were annealed at T > 900 °C, the silicon nanocrystals (nc-Si) enwrapped by amorphous silicon (a-Si) could be observed. The thermal quenching behavior at ⳱ 1.535 m and its relation with the annealling temperature were also investigated. With increasing annealing temperature, the portion of a-Si and the thermal quenching both decreased. Efficient luminescence from Er ions and weak intensity thermal quenching were obtained from the sample annealed at 1100 °C. The role of a-Si in non-radiative processes at T > 100 K is discussed.
I. INTRODUCTION
Integrated optical devices have several attractive characteristics such as a very high rate of data transmission in optical wave-guides and low sensitivity to electromagnetic radiation. Many applications, such as optical interconnections at the chip-to-chip level, require the optimization of active and passive optical functions (e.g., light sources, wave guides, modulators and detectors), and their integration together with electronic functions on the same chip.1,2 It is well known that Si, a semiconductor with the most mature technology, would be the interesting material of choice for a monolithic integration of optical and electrical functions. However, due to its indirect band-gap and the absence of linear electro-optic effect, Si has been considered for a long time unsuitable for optoelectronic applications. It has been proposed a solution to the problem of light emission from Si through the incorporation of Erbium, a rare-earth ion, in the silicon lattice.3 Er ions are characterized by an unfilled 4f shell, which is surrounded by an external close shell. A sharp, atomic-like radiative transition within the 4f shell of these ions can be excitated both optically4 and electrically.5 One of the principal problems in the development of Er-doped Si has been identified to be the strong quenching behavior of both the photo- and electroluminescence from 77 K to room temperature. 5,6 The main limiting steps have been recognized in the
non-radiative decay channels, Auger (with the energy released to free carriers)7 and back-transfer (with the energy transferred back from excited Er to electron-hole couples).8 Wide band-gap forms of silicon hosts, such as porous, amorphous, and nanocrystalline silicon can reduce the quenching of Er luminescence.9,10 Roomtemperature light emission in Er-doped nc-Si has been widely reported. 9–11 The thermal quenching of Er emission is greatly reduced, due to the large mismatch between the nanocrystal band-gap energy and the Er transition energy. However, this ideal strong coupling can only be obtained when Er ions directly couple with nc-Si, corresponding to most of the excessive Si transforms to crystal state by optimal thermal treatment. For this paper, evolutions of the microstructure
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