**2. Light emitting characteristics from silicon AMLEDs**

Light emitting devices (LEDs) have become a subject of growing research interest in recent times. A series of LEDs have been realized in standard Complementary Metal Oxide Silicon (CMOS) technology by Kramer et al., [15] and Snyman et al. in [15–19]. These structures emit light through phonon-assisted intra-band and inter-band recombination phenomena [20–22]. Subsequent devices were developed by Du Plessis et al., which showed increased light emission when additional carriers are injected into avalanching Si n + p light emitting junctions [23, 24]. Further work by Xu et al. led to the realization of a series of CMOS integrated LED devices with third terminal gated control [8]. Subsequently, the temperature, carrier density, and electric field encountered in Silicon Avalanche Mode Light Emitting Devices (Si AMLEDs) were analyzed by Duttal and Steeneken et al. They also suggested operation of gated Si LED operating in the forward-biased mode and emitting in the 1100 nm region [12]. A major advantage with these devices is the realization of high modulation speeds ranging into the GHz due to the reverse bias configuration of Si AMLEDs [25, 26]. Potential applications of these devices can be found in hybrid optical RF systems, on-chip micro-photonic systems, and CMOS-based optical interconnect. In a recent work by Xu and Snyman, they demonstrated enhanced emission intensities of 0.1 to about 200 nW/μm2 from Si AMLEDs in the 650–750 nm emission regime by using enhanced impurity scattering and extended E-field profiling in the device [27, 28].

We present in this chapter a specific p + np + graded junction type Si AMLED device (**Figure 1(a)**) that was realized in a 0.35 micron Si bipolar process with a high frequency RF application capability. This process enabled an "elongated pillar" structure to be etched out on a broad silicon semi-insulating p-substrate. These structures could hence effectively confine the lateral carrier diffusion and

*Nanomaterial-Enhanced Receptor Technology for Silicon On-Chip Biosensing Application DOI: http://dx.doi.org/10.5772/intechopen.94249*

#### **Figure 1.**

*Device design (schematic), considerations of a p + nn + Si avalanche mode LED in RF bipolar integrated circuitry [27] (a) lateral cross-section of the device. (b) Device optical performance characteristics as compared with other previous devices [27]. (c) Spectral characteristics of the emitted optical radiation (for below 570 nm consult Ref. [17]). Inserts show optical emission micrographs of the LEDs taken at normal angles to the surface of the device.*

maximize the diffusing carrier density in the device. The device used n + and p + regions in the substrate region of the silicon, and positioned a distance 1 micron apart from each other. Subsequently, up to 1 micron graded doping profiles were formed at the edges of these regions, while overlapping of dopants occurred in the center region of the device [27]. For illustrative purposes, device design and performance characteristics relative to previous designs are again presented in **Figure 1(b)**. The optical emissions from the device were measured with an Anritso MS9710B Spectrum Analyzer with a lensed-probe optical fiber. The device and the lensed probe were electronically micro manipulated to within 0.1 mm of the light-emitting device. The total emission intensities with cross-sectional conduction areas of about 1 micron square as indicated at the surface of the device was measured to be in the order of 200 nW per μm<sup>2</sup> . **Figure 1(c)** depicts the main spectral components as observed for these types of devices. Clear peaks and prominent peaks of 2.8 eV, 2.3 eV, 1.8 eV, and 1.5 eV were observed in the spectrographic measurements for the devices and are shown in the spectrum when converting the nm emissions to corresponding eV emissions [19, 27]. Overall, the spectrum represent a broad spectrum from 450 nm to about 850 nm with main characteristic peaks at 450 nm (2.8 eV) (blueish), 550 nm (2.0 eV) (greenish), 600 nm (2.3 eV) (reddish), and at 750 to 850 nm (1.5 and 1.8 eV) (infrared). To form the on-chip biosensor, a bio-interaction layer etched from the Si AMLED chip interacts with the evanescent field of a micro dimensioned waveguide. An array of detectors below the receptor cavity selectively monitor reflected light in the UV, visible, infrared and far-infrared wavelength regions.

AgNPs used as immobilization layer in the receptor layer enhances sensitivity and selective absorption of antigens and biomarkers, like the prostate specific antigen (a biomarker for prostate cancer), causing a change in detection signal as a function of propagation wavelength as light is dispersed.
