Carlos Viana

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.

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.

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.

Full area emitter SiGe phototransistor for opto-microwave circuit applications

We present a study of full area emitter phototransistors with different optical window sizes implemented in a SiGe Bipolar technology. Extracted responsivity of 3.5 A/W and an opto-microwave cut-off frequency of 739 MHz were observed.

Modal Noise Mitigation in 850-nm VCSEL-Based Transmission Systems Over Single-Mode Fiber

Various short-range optical connections, transmitting either high-bit-rate digital signals or radio frequency analog signals, can exploit 850-nm vertical-cavity surface-emitting lasers as optical source together with the standard single-mode fiber (SSMF) as optical channel. This solution presents attractive features in terms of reduced cost and energy consumption. However, bandwidth reduction due to intermodal dispersion and undesired fluctuations of the received signal due to modal noise are present in this case. Such effects are studied theoretically and experimentally, and a cost-effective solution is proposed to reduce their impact. Hence, connections with SSMF length up to 300 m with 3-dB bandwidth of 2500 MHz are demonstrated, while the modal noise is reduced to a standard deviation of less than 2 dB.

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.

Study of Lateral Scaling Impact on the Frequency Performance of SiGe Heterojunction Bipolar Phototransistor

The influence of the lateral scaling such as emitter width and length on the frequency behavior of SiGe bipolar transistor is experimentally studied. Electrical transistors of different emitter sizes are designed and fabricated by using a commercial bipolar transistor technology. The effect of peripheral current and collector current spreading on electrical bipolar transistor performances are analyzed in regards to the state of the art. Furthermore, the lateral scaling effect on SiGe phototransistor electrical and opto-microwave frequency behavior is studied. The impact of the lateral flow of photo-generated carriers toward the optical opening in phototransistor structure is investigated. Moreover, the 2-D carrier flow effect on the opto-microwave frequency behavior of the phototransistor is characterized through opto-microwave scanning near-field optical microscopy measurements, in the course of which the intrinsic parameters, such as transit time and junction capacitances are extracted over the surface of the phototransistor. An intrinsic optical transition frequency of 6.5 GHz is measured for

An 850 nm SiGe/Si HPT with a 4.12 GHz maximum optical transition frequency and 0.805A/W responsivity

10\times 10\,\,\mu \text {m}^{2}

Substrate diode effect on the performance of Silicon Germanium phototransistors

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

A 10 × 10 μm2 SiGe heterojunction bipolar photo-transistor (HPT) is fabricated using a commercial technological process of 80 GHz SiGe bipolar transistors (HBT). Its technology and structure are first briefly described. Its optimal opto-microwave dynamic performance is then analyzed versus voltage biasing conditions for opto-microwave continuous wave measurements. The optimal biasing points are then chosen in order to maximize the optical transition frequency (fTopt) and the opto-microwave responsivity of the HPT. An opto-microwave scanning near-field optical microscopy (OM-SNOM) is performed using these optimum bias conditions to localize the region of the SiGe HPT with highest frequency response. The OM-SNOM results are key to extract the optical coupling of the probe to the HPT (of 32.3%) and thus the absolute responsivity of the HPT. The effect of the substrate is also observed as it limits the extraction of the intrinsic HPT performance. A maximum optical transition frequency of 4.12 GHz and an absolute low frequency opto-microwave responsivity of 0.805A/W are extracted at 850 nm.