Kingsley A. Ogudo

Higher Intensity SiAvLEDs in an RF Bipolar Process Through Carrier Energy and Carrier Momentum Engineering

Carrier energy and momentum engineering design concepts have been utilized to realize higher intensity, up to 200 nW.μm -2 in p+nn+ silicon avalanche-based LEDs in a silicon 0.35-μm RF bipolar process. The spectral range is from 600- to 850-nm wavelength region. Best performance are up to 600-nW vertical emission in a 3-μm square active area at 10 V and 1 mA (200 nW.um-2). The achieved emitted optical intensity is about 100 fold better as compared with other published work for nearest related devices. In particular, evidence has been obtained that light emission in silicon are strongly related to scattering mechanisms in a high density n+ dopant matrix of phosphorous atoms in silicon that has been exposed to successive thermal cycles, as well on the optimization of the carrier energy and momentum distributions during such interactions.

Optical propagation and refraction in silicon complementary metal–oxide–semiconductor structures at 750 nm: toward on-chip optical links and microphotonic systems

Abstract. This paper analyzes the optical propagation and refraction phenomena in various complementary metal–oxide–semiconductor (CMOS) structures at 750 nm wavelength. Operation at these wavelengths offers the potential realizations of small microphotonic systems and micro-opto-electro-mechanical systems (MOEMS) in CMOS integrated circuitry, since Si-based optical sources, waveguides, and silicon (Si) detectors can all be integrated on a single chip. It could also increase the optical coupling efficiencies to external optical fibers. With the help of Monte Carlo and RSoft BeamPROP simulations, we demonstrate achievements with regard to optimizing vertical emission, focusing, refraction, splitting and wave guiding in 0.35 to 1.2 μm CMOS technology at 750 nm wavelength. The material properties, refractive indices, and thicknesses of various CMOS over-layers were incorporated in the simulations and analyses. The analyses show that both Si nitride and Si oxi-nitride offer good viability for developing such waveguides. Effective single-mode wave-guiding with calculated loss characteristics of 0.65u2009u2009dB·cm−1, with modal dispersion characteristics of less than 0.2u2009u2009ps·cm−1 and with a bandwidth-length product of higher than 100 GHz-cm seems possible. A first iteration realization of an optical link is demonstrated, utilizing specially designed avalanche-based Si-LEDs and a specially designed first iteration CMOS waveguide. Potential applications of avalanche-based Si LEDs into microphotonic systems and MOEMS are furthermore proposed and highlighted.

Application of Si LEDs (450nm-750nm) in CMOS integrated circuitry-based MOEMS: simulation and analysis

This paper discusses the simulation, development and potential application of Si LEDs in pre-specified complementary metal oxide semiconductors (CMOS) integrated circuit structures in the wavelength range of 450nm - 750nm. A MONTE CARLO simulation technique was developed in which the optical wave propagation phenomena as relevant in CMOS structures were continuously updated as the optical ray progresses through the structure. Refractive index of the material, layers thickness and structure curvatures were all incorporated as ray propagation parameters. By using a multi-ray simulation approach, the overall propagation phenomena wrt refraction, reflection, scattering, and intensities could be evaluated in globular context in any complex CMOS integrated circuit structure in a progressive way. MATLAB software was used as a mathematical capable and programmable language to develop the dedicated software evaluation tool. Subsequently, some first iteration, conceptual, applications of MOEMS structures are demonstrated as implemented in Si CMOS integrated circuitry, utilizing Si InAva LEDs and silicon detectors.

Light Emitting Devices in Si CMOS and RF Bipolar Integrated Circuits

ABSTRACT In this article, we discuss the emission of visible light (400–900 nm) by a monolithically integrated silicon p-n junction under reverse bias. Silicon light emitting devices (Si-LEDs) could be designed and realized utilizing the standard complementary metal oxide semiconductor (CMOS) technology. Increased electroluminescence from the three-terminal MOS-like structure is observed, with the approach of carrier energy and momentum engineering design. Because Si-LEDs, waveguides, and photodetectors (Si) can be integrated on a single chip, a small microphotonic system could be realized in the CMOS integrated circuitry standard platform. The results can be substantially utilized for realizing a complete on-chip optical link.

Light emission in silicon: from device physics to applications

Silicon Photonics is an emerging field of research and technology, where nano-silicon can play a fundamental role. Visible light emitted from reverse-biased p-n junctions at highly localized regions, where avalanche breakdown occurs, can be used to realize a visible electro-optical sources in silicon by means of light-emitting diodes (Si-LEDs) is reviewed by characterizing the spectral distribution. Regarding applications, a monolithic optoelectronic integrated circuit (OEIC) for on-chip optical interconnection based on standard CMOS technology is discussed. Although there are some of the present challenges with regard to the realization of suitable electro-optical elements for diverse integrated circuit applications, the type of silicon light source can be further developed into be a Si-based optical short-distance on-chip optical interconnect applications.

Towards 10 - 40 GHz on- chip micro-optical links with all integrated Si Av LED optical sources, Si N based waveguides and Si-Ge detector technology

Micron dimensioned on-chip optical links of 50 micron length, utilizing 650 – 850 nm propagation wavelength, have been realized in a Si Ge bipolar process. Key design strategies is the utilization of high speed avalanche based Si light emitting devices (Si Av LEds) in combination with silicon nitride based wave guides and high speeds Si Ge based optical detectors. The optical source, waveguide and detector were all integrated on the same chip. TEOS densification strategies and state of the art Si-Ge bipolar technology were further used as key design strategies. Best performances show up to 25 GHz RF carrier modulation and - 40dBm total optical link budget loss with a power consumption of only 0.1 mW per GHz bandwidth. Improvement possibilities still exist. The process used is in regular production. The technology is particularly suitable for application as optical interconnects utilizing low loss, side surface, waveguide to optical fibre coupling.

Silicon Avalanche Based Light Emitting Diodes and Their Potential Integration into CMOS and RF Integrated Circuit Technology

As a rapid growing field in worldwide science and technology, silicon nano-photonics has become one of the most promising photonics integration platforms in the last decade. This is mainly due to the combination of a very high index contrast and the availability of silicon complementary metal-oxide-semiconductor (CMOS) fabrication technology, which allows the use of electronics fabrication facilities to make photonic circuitry. Unfortunately, the indirect band-gap of silicon leads to low efficiency and slow efficiency that is unexpected. The rate of electron-hole recombination in silicon material is too low to produce emitted photons in forward biased silicon p-n junctions, but light emission observed from reverse-biased silicon p-n junctions under high electric field was already reported in 1955 by Newman [1]. The radiative transition between hot carriers emits photons larger than the energy gap. Hence the luminescence during avalanche breakdown is characterized by a broad emission spectrum. An example of the high-energy edges of avalanche-breakdown luminescence is shown in Fig. 1. The low-energy edge of the emission spectrum, on the other hand, extends to energies lower than the gap energy, due to the tunneling-assisted photon emission [2].

High-intensity 100-nW 5GHz silicon avalanche LED utilizing carrier energy and momentum engineering

Graded junction, carrier energy and momentum engineering concepts have been utilized to realize a high intensity 100 nW 5GHz Silicon Avalanche based LED (Si Av LED). A silicon 0.35 micron RF bi-polar process was used as design and processing technology. Particularly, the carrier momentum and energy distributions were modeled in graded junction Silicon p+-i-n structures, and utilized to increase optical yield. Best performance are up to 750nW emission in a 7 micron square active area at 10 V and 1mA. The device show up to 5 GHz modulation bandwidth. The spectral range is from 450 nm to 850 nm with an emphasized components in the white spectral region. The process is greatly CMOS compatible. The technology is particularly suitable for application in futuristic on- chip micro-photonic systems, lab-on chip systems, silicon- based micro display systems, on chip optical links, and optical inter-connects systems.

Development of a 0.75 micron wavelength, all-silicon, CMOS-based optical communication system

The utilization of Organic Light Emitting Diodes (OLEDs) and Si Avalanche LEDs emitting at 0.45 - 0.75 micron enable the development of high speed all -Silicon CMOS based optical communication systems without the incorporation of materials such as Ge or III-V components. The development of low loss and high curvature optical waveguides in CMOS technology at these wavelengths, however, offers major challenges. Advanced optical simulation software was hence used in order to develop effective CMOS based waveguides, using CMOS materials characteristics, processing parameters, and the spectral characteristics of CMOS Av LEDs. The analyses show that both silicon nitride and Si oxi-nitride offer good viability for developing such waveguides, utilizing 0.2 to 1.5 micron wide CMOS over-layer as well as trench-based technology. Particularly, trench based technology are very attractive, since the optical sources can then be integrated with silicon avalanche based LEDs with trench-based waveguides on the same plane with standard CMOS processing procedures. Effective single mode wave-guiding with calculated loss characteristics of 0.65 dB.cm-1 and modal dispersion characteristics of 0.2 ps.cm-1 and with a bandwidth-length product of higher than 100 GHz-cm are predicted.

Realization of 10 GHz minus 30dB on-chip micro-optical links with Si-Ge RF bi-polar technology

Si Avalanche based LEDs technology has been developed in the 650 -850nm wavelength regime [1, 2]. Correspondingly, small micro-dimensioned detectors with pW/μm2 sensitivity have been developed for the same wavelength range utilizing Si-Ge detector technology with detection efficiencies of up to 0.85, and with a transition frequencies of up to 80 GHz [3] A series of on-chip optical links of 50 micron length, utilizing 650 – 850 nm propagation wavelength have been designed and realized, utilizing a Si Ge radio frequency bipolar process. Micron dimensioned optical sources, waveguides and detectors were all integrated on the same chip to form a complete optical link on-chip. Avalanche based Si LEDs (Si Av LEDs), Schottky contacting, TEOS densification strategies, silicon nitride based waveguides, and state of the art Si-Ge bipolar detector technologies were used as key design strategies. Best performances show optical coupling from source to detector of up to 10GHz and - 40dBm total optical link budget loss with a potential transition frequency coupling of up to 40GHz utilizing Si Ge based LEDs. The technology is particularly suitable for application as on-chip optical links, optical MEMS and MOEMS, as well as for optical interconnects utilizing low loss, side surface, waveguide- to-optical fiber coupling. Most particularly is one of our designed waveguide which have a good core axis alignment with the optical source and yield 10GHz -30dB on-chip micro-optical links as shown in Fig 9 (c). The technology as developed has been appropriately IP protected.