Silicon-based optoelectronic devices

Shortly after the observation of visible PL from micro PS at room temperature [Cal], the first EL from a solid-state device was reported [Ri2]. This initiated vigorous research, because silicon-based optoelectronic devices seemed to be within reach. After several years of intense research the potential and the main problems involved with the EL from PS have been clarified. 

However, R-doped semiconductors have evolved into a whole new field due mainly to the hope of obtaining silicon-based optoelectronic devices (Polman et al. 1993), that is, even using an indirect-gap semiconductor with no active optical property of its own. This field has been recently reviewed by Pomrenke et al. (1993). 

In the last few years Schneider and co-workers have performed a number of experiments on various SiC polytypes which exhibit a characteristic infrared emission in the 1.3 to 1.5 pm spectral range [98]. They have assigned this emission band to vanadium impurities substituting the various silicon sites in the lattice. In their extensive work they found three charge states of vanadium which act as an electrically amphoteric deep level in SiC. They also suggest that vanadium may have an important role in the minority-carrier lifetime in SiC-based optoelectronic devices [98,99], Recently, trace amounts of vanadium impurities have been detected in 3C-SiC grown by the modified-Lely technique [100]. 

The future development of porous silicon (PS)-based optoelectronic devices depends on a proper understanding of electrical transport properties of the PS material. Electrical transport in PS is influenced not only by each step of processing and fabrication methods but also by the properties of the initial base substrate. This chapter endeavors to chronologically document how the knowledge base on the nature of carrier transport in PS and the factors governing the electrical properties has evolved over the past years. The topics covered include the proposed electrical transport models including those based on effective medium theories, studies on contacts, studies on physical factors influencing electrical transport, anisotropy in electrical transport, and attempts to classify the PS material. 

Visible photoluminescence (PL) from porous silicon (PS) observed at room temperature has inspired sustained research into its potential application in Si-based optoelectronic devices and its theoretical basis (Canham 1990). This property is reviewed in the handbook chapter Photoluminescence of Porous Silicon. Most PS layers are prepared by anodic etching on/>-type Si substrates, a technique in which metal is often deposited on the rear surface of the Si substrate in order for it to be used as an ohmic back contact (see handbook chapter Porous Silicon Formation by Anodisation ). However, the requirement for a back contact electrode is a limitation of this method for example, it is difficult to form a PS layer on a sihcon-on-insulator (SOI) structure or on Si integrated circuits. A photoetching method, on the other hand, requires no electrodes and allows the formation of a visible luminescence layer on not only single-crystaUine Si substrates but also SOI structures. 

It is highly likely that by the second decade of the new millennium silicon-based computing will have reached fundamental technological or physical limits. Computers will therefore be based on substrates that exhibit superior performance characteristics. One possibility is the photon. Optoelectronic devices, which use substrates such as gallium arsenide, permit the interconversion of electrons and photons. Hybrid computers, which may already be available commercially by 2010, would use silicon for computation and photons for data transfer. The coherent modulation of very-high-frequency light beams enables many high-capacity... 

This movement is a key challenge for the entire field of advanced materials, but it is a particularly exciting challenge for silicon-based polymers. From the point of view of materials, silicon-based polymers span the three traditional domains plastics, ceramics, and metals. Potential applications are equally diverse. Silicon-based polymers range from structural materials, to optoelectronic devices, and to speciality materials for biomedical applications. We are in a unique position to capture the benefits of this merger of materials and polymer science. 

Silicon is the most widely used material in the electronics industry. To develop silicon-based devices for optoelectronic applications, one would like to make silicon a photon-emitting material. Unfortunately, silicon is an indirect gap semiconductor and, thus, the efficiency of photon emission is extremely low since the radiative recombination of the electron-hole pair is not allowed without the assistance of a momentum-conserving phonon. Moreover, the existence of defects leads to an almost total quenching of this rather unlikely process. 

Growing high-quality ZnO on Si substrate has been pursued for its low cost and the advantages of Si-based integration of optoelectronic devices (Suhail et al. 2012). Porous silicon is used as an intermediate layer between silicon and ZnO films, and it provides a large area composed of an array of voids (Chuah et al. 2010). 

Partially functionalized cyclopolysilanes recently attracted attention as model substances for siloxene and luminescent silicon. The yellow luminescent silicon is formed by the anodic oxidation of elemental silicon in HF-containing solutions and may be used for the development of silicon-based materials for light-emitting structures which could be integrated into optoelectronic devices. Because the visible photo luminescence of... 

During the last decade GaAs-based micro- and optoelectronics has developed from a military niche to a global commercial player that does not replace but supplement silicon-based devices. This development has been due to some unique physical properties of compound semiconductors allowing for superior functionality of devices and the progress made in the production of single crystals and wafers/substrates, which has now reached maturity. 

Since 2004 [183], graphene research has evolved from a heavily theoretical and fundamental field into a variety of research areas [301]. Its electrical, magnetic, physical-mechanical, and chemical properties position it as the most promising material for molecular electronic and optoelectronic applications, possibly replacing the currently used silicon and metal oxide based devices. Nonetheless, further research is essential in order to control easily such properties and construct devices with specific and novel architectures to explore in depth all of these exciting properties, as well as to achieve the synthesis of large-scale, size- and layer-count controlled graphene. 

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