Furthermore, reverse-bias implies the evidence that the electroluminescence is not simply induced by the direct recombination of electrons and holes in the forward-biased p-n junctions. 6 Although the interest in optical emission from the integrated silicon devices is growing with the main emphasis on infrared emission for forward-biased LED, we will focus here on the visible light emission from the reverse-biased junctions. 5 For silicon PN junctions, when the reverse-bias of the PN junction reaches avalanching condition, visible electroluminance emitting phenomenon is observed. The PN junction LED could be traced back to 1955 when Newman first reported the light-emitting phenomenon of breakdown radiation from “red spots,” or micro plasmas, in silicon p-n junctions. In contrast to them, silicon diodes designed utilizing conventional very large-scale integration (VLSI) design rules can be fabricated in present technology, using the same masks, which include the other Si-CMOS components. 3 Because of quantum confinement, the band gap of the silicon nanoparticles can become as large as 2 to 3 eV, thus essentially enhancing the radiative recombination. Light-emitting silicon-based materials have been made using band-structure engineering of SiGe and SiC alloy and Si/Ge superlattices, 2 and by exploiting quantum-confinement effects in nanoscale particles and crystallites. The ideas for direct generation (i.e., electron-hole recombination) of light in silicon by the use of photonic-crystal structure remain in the domain of ongoing research, since the spatial confinement of electron-hole pair on silicon nanocrystal separated by a high-barrier oxide is able to reduce the nonradiative recombination probability and increase the luminescence. 1ĭespite the indirect bandgap, one of the most promising candidate light sources is now thought to be silicon itself because LEDs made of silicon-based materials can be integrated into the existing microelectronic and optoelectronic technologies in a highly economic way. A hybrid-integration process known as flip-chip bonding can integrate thousands of optoelectronic devices on a single silicon chip with lateral alignment better than 1 micron. This approach is based on bonding separately fabricated optoelectronic and electronic chips. One practical approach to addressing the mismatch between the compound-semiconductor optoelectronic technology which is used to fabricate optical sources, and the CMOS silicon technology which is the basis of modern electronics, is the hybrid integration. Efficient light-emitting materials, such as AlGaAs / GaAs, grown on silicon substrates by heteroepitaxy are not sufficiently reliable because of the lattice-parameter and thermal-expansion mismatch between the two materials. The main difficulty lies in transmitters since light sources cannot be efficiently made with silicon because it is an indirect-bandgap material. Silicon photo-receiver circuits can be readily embedded in silicon chips, and silicon-on-insulator (SOI) optical waveguides (i.e., SiO 2 layer) may be used as optical connections. Ideally, all three components (i.e., light source, waveguide, and photo-receiver) of the optical link should be monolithically integrated with the silicon substrate chip and be compatible with complementary metal-oxide semiconductor (CMOS) technology. The energy released by the electron may take the form of an emitted photon, in which case the process is called radiative-recombination. ![]() This process, called electron-hole recombination, occurs when an electron decays from the conduction band to fill a hole in the valence band. Traditionally, a light-emitting device (LED) is a forward-biased p-n junction fabricated from a direct-bandgap semiconductor material that emits light via injection electroluminescence. Electroluminescence, first observed in 1907, is a phenomenon in which light is emitted by a material that is subjected to an electric field.
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