Current high speed photon communication system has a big demand for high performance optical detector, especially the high speed silicon-based detector. In this paper, a SiGe heterojunction phototransistor with different Ge-profile in the SiGe base is designed for high optical characteristic frequency. Influences of three types of Ge-distributions (box, triangular, and trapezoidal distribution) and different Ge-content which is in the range of 15%~35% on the frequency performance of SiGe heterojunction phototransistors (HPTs) are analyzed in this paper. A characteristic frequency of 10.52GHz for an 850 nm incident light is achieved by using triangular distribution with 20% Ge-content in the SiGe base.
The emerging hot industries such as 5G communications require a higher demand for Si-based photo detectors, especially the SiGe heterojunction phototransistor with internal gain. But there is a big contradiction between the responsivity optimization and working speed promotion. These cause the difficulty of optimizing the common vertical-illustrated SiGe phototransistor. This paper proposed a novel SiGe ridge waveguide phototransistor and analyzed the influence of the waveguide structure, including base thickness, ridge waveguide width and length, on its optical characteristic frequency and optical gain. The ridge waveguide structure is optimized and obtained finally. When the thickness of the base region is 40nm, the doping concentration is 1.0×1019cm-3, the waveguide length is 50μm, and the ridge width is 1μm, the designed SiGe ridge waveguide phototransistor obtained the optical gain of 6.24 and the maximum characteristic frequency of 12.8GHz under incident light of 850nm.
High speed and high efficiency photodetectors are the key components in optical transmission, optical sensing and optical
processing systems. Except performance requirements, cost control is also an aspect that must be considered in the current
technological development. Therefore, silicon-based high-speed and high-efficiency chip level photodetectors that can be
monolithic integrated with very large-scale CMOS integrated circuits have become the focus of research. SOI structure
provides performance improvement for silicon-based HPT. We demonstrate a SOI-based SiGe Heterojunction
Phototransistor which has greater light absorption compared with Si-based HPT. The influence of SOI structure on
absorption and collector current of SiGe heterojunction phototransistor (HPT) are simulated and analyzed in this paper.
When the optical power is 10mw, the collector current in SOI-based HPT reported in this paper can reach 4.6mA with
5.83% of light absorption calculated, while the collector current in Si-based HPT is 3.35mA with 4.48% of light absorption
calculated under 940nm wavelength. The peak responsivity with SOI structure exhibits 2.82A/W which is enhanced by
12.8% than that of Si-based HPT.
In vivo optogenetics provide special and powerful capabilities in regulation of neurons, research of neural circuits and even in treatment of brain diseases. However, conventional hardware for such studies tethers the experimental animals to remote light sources, power sources, or other functional modules, which imposes considerable physical constrains on natural behaviors and limits the range of the experiment. To enable flexible and convenient optogenetic manipulation of neural circuit with finite disruption of animal behavior, a wirelessly powered optoelectronic device, composing mainly of a radio frequency (RF) energy harvester and a high-performance GaN-based light-emitting diode (LED), is demonstrated and can be used to construct an implantable optrode for optogenetics. The wireless RF power signal is collected through an antenna and a two-stage voltage doubling rectifier circuit, and finally converted into high-amplitude DC voltage. Provided with 25-dBm RF power with a distance of 0.2 m, the RF energy harvesting and processing circuit can output a stable 2.81 V DC voltage and drive the designed GaN-based LED to work normally. After being successfully lit, the emission peak wavelength of the LED locates 455 nm and the output optical power density reaches 214.9 mW / mm2, which is fully capable of activating light-sensitive ion channel channelrhodopsin-2. The total area of the device is 3 mm × 3.2 mm, which is suitable for subdermal implantation.
Large scale optoelectronic monolithic integration for optical fiber communication makes more and more optoelectronic
active devices and passive components integrate into a single chip. It is necessary to provide enough wide gain spectrum
to satisfy the requirement from each device. In this paper, based the analysis on the gain spectrum of InGaAsP/InP
quantum well, the dependence of its gain spectrum bandwidth on the well width and doping concentration was derived.
An asymmetric quantum well with the same doping concentration and different well width was design to realize the
destination. The simulation results prove that the asymmetric quantum well indeed make the gain spectrum wider. Then
the asymmetric quantum wells were grown successfully by low pressure MOCVD at 665°C. The full width at half
maximum (FWHM) of 115nm was observed in its amplified spontaneous emission (ASE) spectrum, which was flatter
and wider than that of the symmetric quantum wells.
For device analysis and optimization, a model based on Transfer Matrices Method was built to simulation the
performance of a new integrated device. This novel DFB laser was composed of two serial sections to provide selectable
wavelengths. The periods of two Bragg gratings were different and were chosen to achieve a spacing of 20nm between
the two corresponding Bragg wavelengths. The model is more simple and convenient to simulate optical integrated
device than other direct simulation methods used before. The simulation results prove that this novel waveguide structure
of the serial DFB lasers is feasible. The integrated optical device was fabricated and two wavelengths of 1.51um and
1.53um were realized under different work conditions.
Width varied quantum wells show a more flat and wide gain spectrum (about 115nm) than that of identical miltiple quantum well. A new fabricating method was demonstrated in this paper to realize two different Bragg grating in an identical chip using traditional holographic exposure. A wavelength selectable DFB laser based on this material grown by MOVPE was presented. Two stable distinct single longitudinal mode of 1510nm and 1530nm with SMSR of 45 dB were realized.
Optoelectronic packaging has become a most important factor that influences the final performance and cost of the module. In this paper, low microwave loss coplanar waveguide(CPW) on high resistivity silicon(HRS) and precise V groove in silicon substrate were successfully fabricated. The microwave attenuation of the CPW made on HRS with the simple process is lower than 2 dB/cm in the frequency range of 0~26GHz, and V groove has the accuracy in micro level and smooth surface.These two techniques built a good foundation for high frequency packaging and passive coupling of the optoelectronic devices. Based on these two techniques, a simple high resistivity silicon substrate that integrated V groove and CPW for flip-chip packaging of lasers was completed. It set a good example for more complicate optoelectronic packaging.
In this paper, a quasi-three-dimension theoretical model for the Vertical-Cavity Surface-Emitting Laser with oxide-confined layers is showed. The distributions of the equal-potential line, injected current density, carrier concentration and the optical field distribution in the cavity are calculated self-consistently by the finite difference method. The influences of the light output window's radius and oxide-confined layers window's radius are studied. At the same time, we study the influence of the N-type DBR on some characteristics of the VCSEL. The results show that there would be a large difference with practical VCSEL ifthe N-type DBR layers were neglected.
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