**1. Introduction**

Biosensors and lab-on-chip (LOC) devices have become a subject of growing professional interest world-wide. This is evident in the growing number of scientific publications, and the astronomical growth in the world market for biosensors and lab-on-chip devices over the past ten years. This has been possible, on a large part, due to rapid improvements in sensing techniques, innovation and growth in the development of new biomaterials such as conducting polymers, copolymers and sol-gels, multiplexing capabilities that promote versatility in new generation sensor devices, the possibility of integration on standard silicon integrated circuit chip,

and miniaturization possibilities down to micro- and nano-dimensions. Recently, researchers have been successful in developing light emitting devices that can be realized in standard silicon integrated circuitry, and have also proposed diverse applications for these in the future [1–5]. The main advantage of these devices may be the ease of integration into mainstream silicon manufacturing technology such as complementary metal oxide silicon (CMOS) and radio frequency (RF) bipolar technologies. Through recent research, light emission from silicon devices has been achieved in various reverse-biased p-n avalanche structures. This development has now been nomenclated as "silicon light-emitting diodes that operate in the reverse avalanche mode" (Si AMLEDs) [6–10]. If the detailed dispersion characteristics observed per solid angle for a particular device is known, it can enable the design of novel and futuristic on-chip electro-optic applications. Examples of such applications could include wavelength multiplexers for on-chip communication, diverse futuristic on-chip micro- and nano-dimensioned gas sensors and even on-chip biosensors [11–14]. In this chapter, a two-junction micro-dimension p + −np + Silicon Avalanche-based Light Emitting Device (Av Si LED) has been analyzed in terms of radiation geometrical dispersion characteristics, and with particular interest in the different wavelengths of light (colors) being emitted at different emission angles from the surface of the device. It is worthy of note that the detailed dispersion characteristics will be a function of the device structure, the number of transparent over layers with each having different optical refractive index, and even the final topography or curvature of the various surface layers.
