High-speed silicon electrooptic Modulator design

An electrically driven Mach-Zehnder waveguide modulator based on high-index contrast silicon split-ridge waveguide technology and electronic carrier injection is proposed. The excellent optical and carrier confinement possible in high-index contrast waveguide devices, together with good thermal heat sinking and forward biased operation, enables high-speed modulation with small signal modulation bandwidths beyond 20 GHz, a V/sub /spl pi// times length figure of merit of V/sub /spl pi//L=0.5 V/spl middot/cm and an insertion loss of about 4 dB. The modulator can be fabricated in a complementary metal-oxide-semiconductor compatible way.     

Electroabsorption modulation at 1.3 /spl mu/m on GaAs substrates using a step-graded low temperature grown InAlAs buffer

We have achieved quantum confined Stark effects (QCSE) on In/sub 0.38/Ga/sub 0.62/As-In/sub 0.38/Al/sub 0.62/As multiple-quantum-well (MQW) structures, operating at 1.3 /spl mu/m grown on GaAs substrates. A quantum confined Stark shift of the exciton absorption peak of 47 meV was obtained with an applied electric field of 190 KV/cm, measured on surface normal PIN diodes. The structure is grown by MBE on a novel three-stage, compositionally step graded, In/sub x/Al/sub 1-x/As buffer, doped with Si to 5/spl middot/10/sup 17//cm/sup 3/, on an n-type GaAs substrate. The total thickness of the buffer is 0.3-0.6 mm, which is considerably smaller than that of linearly graded buffer layers. This structure can be used in both waveguide modulators and surface normal F-P type modulators on GaAs substrates.     

Tunable infrared modulator and switch using Stark shift in stepquantum wells

A tunable infrared modulator and/or switch using intersubband Stark shift in a step quantum well is discussed. The device utilizes the intersubband absorption and the large change of separation between energy levels in the step quantum well under an applied electric field. The incident infrared beam on the device is either absorbed or transmitted depending on the energy separation of the levels, and thus the modulation can be achieved by adjusting the energy levels with an applied electric field. The extremely short lifetime of the intersubband transition makes this modulator suitable for application in high-speed long-wavelength optical communications     

High-frequency modulation characteristics of 1.3-/spl mu/m InGaAs quantum dot lasers

In this letter, we report results of small-signal modulation characteristics of self-assembled 1.3-/spl mu/m InGaAs-GaAs quantum dot (QD) lasers at room temperature. The narrow ridge-waveguide lasers were fabricated with multistack InGaAs self-assembled QDs in active region. A high characteristic temperature of T/sub o/=210 K with threshold current density of 200A/cm/sup 2/ was obtained. Small-signal modulation bandwidth of f/sub -3 dB/=12 GHz was measured at 300 K with differential gain of dg/dn/spl cong/2.4/spl times/10/sup -14/ cm/sup 2/ from detailed characteristics. We observed that a limitation of modulation bandwidth in high current injection appeared with gain saturation. This property can direct future high-speed QD laser design.     

Low-cost, high-efficiency, and high-speed SiGe phototransistors in commercial BiCMOS

We present a new approach to obtain low-cost and high-performance SiGe phototransistors in a commercial BiCMOS process. Photoresponsivity of 2.7 A/W was obtained for 850-nm detection due to the transistor gain, corresponding to 393% quantum efficiency. Responsivities of 0.13 A/W and 0.07mA/W were achieved for 1060 and 1310 nm with SiGe absorption. With V/sub ce/=2 V, we measure a -3-dB bandwidth of up to 5.3 GHz for phototransistors with a 4-/spl mu/m/sup 2/ active area and 2.0 GHz for phototransistors with 60-/spl mu/m/sup 2/ active area and finger contacts. This high-efficiency and high-speed phototransistor is an enabling device for monolithic receiver integration.     

Monolithically integrated InGaAs-AlGaInAs Mach-Zehnder Interferometer optical switch using quantum-well intermixing

A highly efficient monolithically integrated Mach-Zehnder interferometer (MZI) optical switch based on a 1.5-/spl mu/m InGaAs-AlGaInAs multiple-quantum-well structure is reported. The device was fabricated by integrating phase shifter sections with bandgap-shifted low-loss waveguides obtained by a single step sputtered SiO/sub 2/-annealing quantum-well intermixing technique. Evaluation of the refractive index change induced by current injection (plasma, band-filling, band-shrinkage effects) and applied electric field (quantum confined Stark effect) based on the MZI was investigated. A device with an active length of 400 /spl mu/m in one of the MZI arms had an extinction ratio /spl ges/20 dB with a half-wavelength current (I/sub /spl pi//) and half-wavelength voltage V/sub /spl pi// as low as 3.2 mA and 3.5 V (1.9 V in push-pull configuration), respectively.     

High-speed mid-IR modulator using Stark shift in step quantum wells

We show in calculations that there is a capability for high speeds with a low applied voltage in modulators based on intersubband transitions in step quantum wells (QWs). A waveguide based on surface plasmons is assumed to achieve the necessary tight confinement of the optical field. In a structure with 8 GaInAs-AlGaInAs-AlInAs step QWs, we obtain a device capacitance of 14 fF corresponding to a RC limitation of electrical f_{3 dB}=190 GHz. The extinction ratio of 6.6-μm light is 10 dB at an applied voltage of 0.9 V and T=300 K. By simple reasoning, we find that the device capacitance is approximately proportional to the absorption linewidth cubed when the linewidth is considered in the device design. Thus, the linewidth is very decisive for the modulation speed. We propose to place the dopants asymmetrically in the barriers in order to reduce broadening caused by doping induced potential fluctuations. In addition, the doping levels in the outermost barriers of the multi-QW structure are proposed to be reduced and asymmetrical, in order to achieve a uniform electric field over the step QWs, which is shown to increase the achievable f_{3 dB} very markedly     

Damping-limited modulation bandwidths up to 40 GHz in undoped short-cavity In/sub 0.35/Ga/sub 0.65/As-GaAs multiple-quantum-well lasers

We demonstrate record direct modulation bandwidths from MBE-grown In/sub 0.35/Ga/sub 0.65/As-GaAs multiple-quantum-well lasers with undoped active regions and with the upper and lower cladding layers grown at different growth temperatures. Short-cavity ridge waveguide lasers achieve CW direct modulation bandwidths up to 40 GHz for 6/spl times/130 /spl mu/m/sup 2/ devices at a bias current of 155 mA, which is the damping limit for this structure. We further demonstrate large-signal digital modulation up to 20 Gb/s (limited by the measurement setup) and linewidth enhancement factors of 1.4 at the lasing wavelength at threshold of /spl sim/1.1 /spl mu/m for these devices.     

InGaAs-InP mesa DHBTs with simultaneously high f/sub /spl tau// and f/sub max/ and low C/sub cb//I/sub c/ ratio

We report an InP-InGaAs-InP double heterojunction bipolar transistor (DHBT), fabricated using a conventional triple mesa structure, exhibiting a 370-GHz f/sub /spl tau// and 459-GHz f/sub max/, which is to our knowledge the highest f/sub /spl tau// reported for a mesa InP DHBT-as well as the highest simultaneous f/sub /spl tau// and f/sub max/ for any mesa HBT. The collector semiconductor was undercut to reduce the base-collector capacitance, producing a C/sub cb//I/sub c/ ratio of 0.28 ps/V at V/sub cb/=0.5 V. The V/sub BR,CEO/ is 5.6 V and the devices fail thermally only at >18 mW//spl mu/m/sup 2/, allowing dc bias from J/sub e/=4.8 mA//spl mu/m/sup 2/ at V/sub ce/=3.9 V to J/sub e/=12.5 mA//spl mu/m/sup 2/ at V/sub ce/=1.5 V. The device employs a 30 nm carbon-doped InGaAs base with graded base doping, and an InGaAs-InAlAs superlattice grade in the base-collector junction that contributes to a total depleted collector thickness of 150 nm.     

Quantum interference, Stark, and carrier density infraredelectrooptical modulation based on intersubband transitions inasymmetrical quantum wells

A new approach toward studying electrooptic modulation utilizing intersubband transitions in quantum wells is presented. Using first-order perturbation theory for analyzing the effect of a dc electric field on the linear susceptibility, an understanding of the mechanisms which give rise to intersubband electrooptic susceptibility is presented. This includes modulation due to the dc Stark effect, modulation due to coherent interference of the envelope states, and modulation of the carrier densities in populated subbands. We study several structures that maximize the electrooptic susceptibility of a particular origin and discuss the suitability of the various schemes for practical realizations. Finally, we derive a figure of merit for each type of modulator, taking into account the linear intersubband absorption, and show that highly efficient near-infrared modulators that operate at a wavelength of 1.5 μm can be realized     

High-responsivity high-gain In/sub 0.53/Ga/sub 0.47/As-InP quantum-well infrared photodetectors grown using metal-organic vapor phase epitaxy

We report the growth and fabrication of bound-to-bound In/sub 0.53/Ga/sub 0.47/As-InP quantum-well infrared photodetectors using metal-organic vapor phase epitaxy. These detectors have a peak detection wavelength of 8.5 /spl mu/m. The peak responsivities are extremely large with R/sub pk/=6.9 A/W at bias voltage V/sub b/=3.4 V and temperature T=10 K. These large responsivities arise from large detector gain that was found to be g/sub n/=82 at V/sub b/=3.8 V from dark current noise measurements at T=77 K and g/sub p/=18.4 at V/sub b/=3.4 V from photoresponse data at T=10 K. The background-limited temperature with F/1.2 optics is T/sub BLIP/=65 K for 0相似文献   

Thermo-optical modulation at /spl lambda/=1.5 /spl mu/m in an /spl alpha/-SiC-/spl alpha/-Si-/spl alpha/-SiC planar guided-wave structure

A planar waveguide based on an amorphous silicon-amorphous silicon carbide heterostructure is proposed for the realization of passive and active optical components at the wavelengths /spl lambda/=1.3-1.5 /spl mu/m. The waveguide has been realized by low temperature plasma enhanced chemical vapor deposition and is compatible with the standard microelectronic technologies. Thermo-optical induced modulation at /spl lambda/=1.5 /spl mu/m is demonstrated in this waveguide. Numerical simulations predict that operation frequencies of about 3 MHz are possible. The measurements have also allowed the determination of the previously unknown thermo-optical coefficient of undoped amorphous silicon at this wavelength.     

A fully integratable 1.55-/spl mu/m wavelength continuously tunable asymmetric twin-waveguide distributed Bragg reflector laser

We demonstrate a single-frequency continuously tunable three-section distributed Bragg reflector laser operating at a center wavelength of /spl lambda//sub 0/=1.548 /spl mu/m using a fully integratable asymmetric twin-waveguide structure. A low-loss tapered mode transformer couples the light between the active waveguide, or gain region, and the passive ridge waveguide where the phase and grating tuning sections are located. The device has a threshold current of 50 mA and output power of nearly 13 mW, with a slope efficiency of 0.12 W/A and a tuning range of 4.8 nm under pulsed operation. An independent phase section is used to continuously tune the wavelength, thus avoiding mode hops. Using a delayed self-heterodyne technique, we determine the linewidth to be (146/spl plusmn/2) kHz.     

Maximum Efficiency of a Two Arm Waveguide Junction (Correspondence)

It is well-known that the efficiency of a two-arm waveguide junction (2-port) depends upon the reflection coefficient /spl Gamma//sub L/ of the load with which one of the arms is terminated. The efficiency is known to vary between the limits 0 and /spl eta//sub m/ (maximum efficiency) as /spl Gamma//sub L/ assumes all possible values within the unit circle. However, there seems to be no published analysis from which one can determine the particular /spl Gamma//sub L/ giving maximum efficiency if the characteristics of the waveguide junction are known.     

Optical and electrical properties of nanostructured metal-silicon-metal photodetectors

We report an experimental evaluation of the performance of silicon (Si) photodetectors incorporating one-dimensional (1-D) arrays of rectangular and triangular-shaped nanoscale structures within their active regions. A significant (/spl sim/2/spl times/) enhancement in photoresponse is achieved in these devices across the 400- to 900-nm spectral region due to the modification of optical absorption properties that results from structuring the Si surface on physical optics scales smaller than the wavelength, which both reduces the reflectivity and concentrates the optical field closer to the surface. Both patterned (triangular and rectangular lineshape) and planar Ni-Si back-to-back Schottky barrier metal-semiconductor-metal photodetectors on n-type (/spl sim/5/spl times/10/sup 14/ cm/sup -3/) bulk Si were studied. 1-D /spl sim/50-250-nm linewidth, /spl sim/1000-nm depth, grating structures were fabricated by a combination of interferometric lithography and dry etching. The nanoscale grating structures significantly modify the absorption, reflectance, and transmission characteristics of the semiconductor: air interface. These changes result in improved electrical response leading to increased external quantum efficiency (from /spl sim/44% for planar to /spl sim/81% for structured devices at /spl lambda/=700 nm). In addition, a faster time constant (/spl sim/1700 ps for planar to /spl sim/600 ps for structured at /spl lambda/=900 nm) is achieved by increasing the absorption near the surface where the carriers can be rapidly collected. Experimental quantum efficiency and photocurrents results are compared with a theoretical photocurrent model based on rigorous coupled-wave analysis of nanostructured gratings.     

Highly coherent electronically tunable waveguide extended cavity diode laser

A frequency agile extended cavity diode laser using an integrated Bragg reflector in a Ti : Fe : LiNbO/sub 3/ waveguide is developed and characterized. The laser emits up to 7 mW in the 1.5-/spl mu/m telecommunication window. The emission spectrum exhibits a 18-kHz linewidth, >40-dB sidemode suppression ratio, and a wavelength stability of /spl plusmn/1 pm over hours. Very fast mode hop-free frequency tuning is achieved through the electrooptic effect, with a tuning slope of 55.5 MHz/V.     

Wideband coplanar waveguide-to-rectangular waveguide transition using fin-line taper

This letter introduces a new wideband coplanar waveguide-to-rectangular waveguide transition. The transition uses a uniplanar circuit in line with the waveguide, which eases the design and fabrication. The design does not require airbridges. Simulations and measurements of X-band (8.2-12.4 GHz) transitions based on both a low- and high-permittivity material (/spl epsiv//sub r/= 2.33 and 10.8) show that the transition works fine over the full frequency band. For /spl epsiv//sub r/= 2.33 the measured return and insertion loss of a back-to-back transition are more than 16 dB and less than 0.4dB, respectively. The corresponding values for /spl epsiv//sub r/= 10.8 are more than 10 dB and less than 1.0 dB, respectively, over 90% of the frequency band. The measured insertion loss values indicate losses of less than 0.14 dB and 0.36 dB at the center frequency for a single transition on a substrate with /spl epsiv//sub r/= 2.33 and 10.8, respectively.     

InGaAs-AlAsSb quantum cascade structures emitting at 3.1 /spl mu/m

A report is made of the pulsed operation of In/sub 0.53/Ga/sub 0.47/As-AlAs/sub 0.56/Sb/sub 0.44/ quantum cascade structures on an InP substrate. The very large conduction band offset (/spl sim/1.6 eV) of this material system made it possible to observe electroluminescence at /spl lambda//spl sim/3.1 /spl mu/m, the shortest emission wavelength yet observed for any intersubband device.     

InGaAs/InP DHBTs with 120-nm collector having simultaneously high f/sub /spl tau//, f/sub max//spl ges/450 GHz

InP/In/sub 0.53/Ga/sub 0.47/As/InP double heterojunction bipolar transistors (DHBT) have been designed for increased bandwidth digital and analog circuits, and fabricated using a conventional mesa structure. These devices exhibit a maximum 450 GHz f/sub /spl tau// and 490 GHz f/sub max/, which is the highest simultaneous f/sub /spl tau// and f/sub max/ for any HBT. The devices have been scaled vertically for reduced electron collector transit time and aggressively scaled laterally to minimize the base-collector capacitance associated with thinner collectors. The dc current gain /spl beta/ is /spl ap/ 40 and V/sub BR,CEO/=3.9 V. The devices operate up to 25 mW//spl mu/m/sup 2/ dissipation (failing at J/sub e/=10 mA//spl mu/m/sup 2/, V/sub ce/=2.5 V, /spl Delta/T/sub failure/=301 K) and there is no evidence of current blocking up to J/sub e//spl ges/12 mA//spl mu/m/sup 2/ at V/sub ce/=2.0 V from the base-collector grade. The devices reported here employ a 30-nm highly doped InGaAs base, and a 120-nm collector containing an InGaAs/InAlAs superlattice grade at the base-collector junction.     

A high current gain 4H-SiC NPN power bipolar junction transistor

This work reports the development of high power 4H-SiC bipolar junction transistors (BJTs) by using reduced implantation dose for p+ base contact region and annealing in nitric oxide of base-to-emitter junction passivation oxide for 2 hours at 1150/spl deg/C. The transistor blocks larger than 480 V and conducts 2.1 A (J/sub c/=239 A/cm/sup 2/) at V/sub ce/=3.4 V, corresponding to a specific on-resistance (R/sub sp on/) of 14 m/spl Omega/cm/sup 2/, based on a drift layer design of 12 /spl mu/m doped to 6/spl times/10/sup 15/cm/sup -3/. Current gain /spl beta//spl ges/35 has been achieved for collector current densities ranging from J/sub c/=40 A/cm/sup 2/ to 239 A/cm/sup 2/ (I/sub c/=2.1 A) with a peak current gain of 38 at J/sub c/=114 A/cm/sup 2/.