Silicon-Based Optoelectronics
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semiconductor photodiodes. In addition, we watch various display units, we use electrooptic
and acoustooptic modulators, parametric amplifiers and all the devices of nonlinear optics, where optical ferroelectrics or complex polymers are the materials of choice. Looking at the "zoo" of materials that are in use for photonics and comparing them to the relatively homogeneous silicon world of electronics, it makes sense to ask whether silicon technology and photonics may be brought together more closely. Today industry's solution is to use discrete components or "MCMs", i. e. multi-chip-moduls, which combine optoelectronic and microelectronic IC's within one package. Are there different answers? We believe that there are many different routes to be explored, leaving the famous silicon roadmap and giving research the opportunity to explore new silicon-based optoelectronic concepts and devices. Some optoelectronic demands can be well satisfied by silicon, even though it has an indirect bandgap and therefore a fairly bad coupling of electron-hole-pairs to photons. For instance, silicon solar cells are very common by now. They convert sunlight photons to electrical power. Silicon is not even the best material for this purpose, but the very mature Si technology and its reasonable efficiency make Si solar cells the most economical choice. Of course, they are slow and bit rates are not a factor for solar cells. But amazingly, even ultra-fast photonic detectors can be realized by silicon technology, as we will show below. 3 Mat. Res. Soc. Symp. Proc. Vol. 486 ©1998 Materials Research Society
And there are more photonic functions, which can be well fulfilled by silicon devices. These proceedings give an informative cross-section through many aspects and we expect to see interesting new ideas and data, new device concepts or prototypes. Nobody should expect a high power solid state laser, based on Si, or an intense coherent blue light source from Si nanoparticles. But if the research efforts lead to a few optoelectronic functions, which can be realized cost effectively by silicon-based devices, this is a very worthy goal already. Because we have seen many new developments inthe last years, we also expect new opportunities in the future. At present, the field is moving rapidly [1, 2]. Table 1 gives a guideline for some silicon-based optoelectronic functions. Although incomplete, it helps to make two points:
a) One has to distinguish between devices operating at photon energies lower than the Si bandgap (IR) and those operating at higher energies (in the visible).
b) Some optoelectronic functions are fulfilled by silicon itself: doped pn-junctions, nanoparticles, porous Si, Si-waveguides in the IR, and Si-detectors. Other devices are based on very different materials, deposited or grown on silicon wafers: modulators, amplifiers and many forms of waveguides. This so-called "Silicon-breadboard-technology" uses the performance of non-silicon materials and has to meet the challenge of compatibility with standard Si technology. At
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