A 440-ps 64-bit adder in 1.5-V/0.18-μm partially depleted SOItechnology

A 64-bit adder in 1.5-V/0.18-μm partially depleted SOI technology, CMOS8S, and techniques to maintain performance are described. CMOS7S SOI, a 1.8-V/0.22-μm partially depleted SOI technology, achieves a 28% speed increase over bulk CMOS7S, and CMOS8S SOI delivers an additional 21%. In a 660-MHz CMOS8S SOI processor, the adder compensates for floating body effects in SOI devices which cause history effects, bipolar currents, and lower noise margins on dynamic circuits     

Threshold currents of 1.3-μm bulk, 1.55-μm bulk, and1.55-μm MQW DFB P-substrate partially inverted buried heterostructurelaser diodes

We investigate the threshold currents of 1.3-μm bulk, 1.55-μm bulk, and 1.55-μm multi-quantum-well (MQW) distributed feedback (DFB) P-substrate partially inverted buried heterostructure (BH) laser diodes experimentally and theoretically. In spite of the larger internal loss of the 1.55-μm bulk laser diodes, the threshold current of the 1.55-μm bulk DFB P-substrate partially inverted BH laser diode is almost the same as that of the 1.3-μm bulk DFB P-substrate partially inverted BH laser diode. The experimentally obtained average threshold current of the 1.3-μm bulk DFB P-substrate partially inverted BH laser diodes is 17 mA and that of the 1.55 μm bulk DFB P-substrate partially inverted BH laser diodes is 16 mA. The calculated threshold current of the 1.3-μm bulk DFB laser diode is 15.3 mA and that of the 1.55-μm bulk DFB laser diode is 18.3 mA, which nearly agree with the calculated values, respectively. We have fabricated two types of five-well 1.55-μm InGaAs-InGaAsP MQW DFB P-substrate partially inverted BH laser diodes. One has barriers whose bandgap energy corresponds to 1.3 μm, and the other has barriers of which bandgap energy corresponds to 1.15 μm. The calculated threshold current of the MQW DFB laser diode with the barriers (λ_g =1.3 μm) is 8.5 mA, which nearly agrees with the experimentally obtained value of 10 mA. However, the calculated threshold current of the MQW DFB laser diode with the barriers (λ_g=1.15 μm) is 7.9 mA which greatly disagrees with the experimentally obtained value of 19 mA, which suggests that the valence band discontinuity between the well and the barrier severely prevents the uniform distribution of the injected holes among five wells     

Small-signal analysis of 1.3-μm microcavity light-emittingdiodes

The modulation speed of 1.3-μm microcavity light-emitting diodes (MCLEDs) has been measured using a small-signal modulation analysis. A speed of 260 MHz using a 25-μm diameter sample at current density of 10 kA/cm² has been achieved. The carrier confinement has been calculated for several carrier densities in order to investigate the origin of the speed limitation. By comparing the performance of the 1.3-μm MCLEDs with that of the 990-nm devices we conclude that the limiting factor on the speed seems to be a lack of carrier confinement in the quantum wells and not a cavity effect     

High-coupling-efficient 1.3-μm laser diodes with goodtemperature characteristics

We have proposed uniformly beam-expanded structures based on the advanced concept for realizing high coupling efficiency and good temperature characteristics. Beam expansion (optical confinement reduction) by narrowing the core layer width as well as a carrier confinement are strongly enhanced by adopting a larger bandgap InGaAsP for MQW barriers and separate confinement heterostructure layers. These laser diodes (LD's) were fabricated by the conventional buried heterostructure laser process, which is very important in reducing the cost. Our results have proven the effectiveness of our proposition. The LD's with high coupling efficiency (-3.2 dB) and good temperature characteristics have been achieved even using the simple approach of reducing optical confinement. The threshold currents at 25 and 85°C are 9.3 and 39.4 mA, respectively. The slope efficiency at 25°C is 0.39 W/A and still high (0.26 W/A) even at 85°C     

Low-threshold oxide-confined 1.3-μm quantum-dot laser

Data are presented on low threshold, 1.3-μm oxide-confined InGaAs-GaAs quantum dot lasers. A very low continuous-wave threshold current of 1.2 mA with a threshold current density of 28 A/cm² is achieved with p-up mounting at room temperature. For slightly larger devices the continuous-wave threshold current density is as low as 19 A/cm²     

Slab-coupled 1.3-μm semiconductor laser with single-spatiallarge-diameter mode

A high brightness semiconductor diode laser structure, which utilizes a slab-coupled optical waveguide region to achieve several potentially important advances in performance, is proposed and experimentally demonstrated using a simple rib waveguide in an InGaAsP-InP quantum-well structure operating at 1.3-μm wavelength. These lasers operate in a large low-aspect-ratio lowest-order spatial mode, which can be butt coupled to a single-mode fiber with high coupling efficiency     

1.3-μm AlGaInAs-InP buried-heterostructure lasers with modeprofile converter

AlGaInAs buried-heterostructure (BH) lasers with a mode profile converter (MPC) have been successfully fabricated for the first time. The thickness of the multiple-quantum-well (MQW) waveguide was vertically tapered by selective area growth (SAG). The threshold current I_th was 14.6 mA with a 600-μm-long cavity and a high-reflective-coated rear facet. The full-width at half-maximum of the far-field pattern in the perpendicular and horizontal directions were 9.2° and 12.6°, respectively. The optical coupling loss between lasers with MPC and a single-mode fiber was 3.0 dB when the distance between the laser and fiber was 20 μm     

Crosstalk characteristics of a 1.3-μm/1.5-μm wavelengthdemultiplexing photodetector using laser-assisted MOMBE growth

This paper demonstrates a monolithic 1.3-μm/1.5-μm wavelength demultiplexing photodetector fabricated using Ar ion laser-assisted metal organic molecular beam epitaxy (MOMBE) growth. Reduction of crosstalk to -24 dB is accomplished in both 1.3-μm and 1.5-μm wavelength regions. The dependence of the crosstalk on the coupling efficiency between the fiber and device and the polarization dependence of the responsivity is also discussed     

High-temperature characteristics of 1.3-μm InAsP-InAlGaAs ridgewaveguide lasers

High-temperature characteristics of InAsP-InAlGaAs strained multiquantum-well (MQW) lasers with a large conduction band discontinuity (ΔE_c) are demonstrated. The InAsP-InAlGaAs MQW ridge waveguide lasers with narrow stripes exhibited a characteristic temperature as high as 143 K in the range from 25°C to 85°C. This material system is promising for developing a cooling-system-free 1.3-μm laser     

1.3-μm Pr-doped In-Ga-based fluoride fiber amplifiers pumped bygrating-fiber-pigtailed 0.98-μm-band laser diodes with a detunedwavelength of 1 μm

At most efficient pump wavelength, a praseodymium-doped In-Ga-based fluoride fiber is directly pumped by four 0.98-μm-band laser diodes. These lasing wavelengths are detuned from 0.98 to 1 μm by external selective optical feedback from fiber grating reflectors. Maximum signal output power of +13.5 dBm is obtained at 1.296 μm. Four-wavelength multiplexed signals at 1.296-1.311 μm are amplified with a deviation of gain less than 1.9 dB. By using the amplifier as a power booster, data of 2.5 Gb/s is successfully transmitted more than 100 km     

Sub-1/4-μm dual-gate CMOS technology using in-situ dopedpolysilicon for nMOS and pMOS gates

A new dual poly-Si gate CMOS fabrication process is proposed. The incorporated technology features a boron-penetration-resistant MBN gate structure for pMOSFET's, and a dual poly-Si gate CMOS process involving separate depositions of in-situ doped n⁺ and p⁺ poly-Si for the nMOS and pMOS gates, 0.2-μm CMOS devices with 3.5-nm gate oxide have been successfully fabricated. The advantages of the new process are demonstrated on these test devices. A CMOS 1/16 dynamic frequency divider fabricated by the new process functions properly up to 5.78 GHz at a 2-V supply voltage     

High-frequency performances of a partially depleted 0.18-μmSOI/CMOS technology at low supply voltage-influence of parasiticelements

This paper shows for the first time the high-performances of a partially depleted 0.18-μ_m technology at low supply voltage. The SOI technology uses a standard digital process with a TiSi ₂ salicided polysilicon gate and a low dose SIMOX substrate. The process does not include any specific feature like T-gate, or high-resistivity SOI substrate. At 1 V, and 2 GHz the current gain and the unilateral power gain are higher than 15 dB for both 0.18 μm gate length NMOS and PMOS transistors. At 1.5 V, the 0.18-μm NMOS and PMOS show a transition frequency of, respectively, 51 GHz and 23 GHz and a maximum oscillation frequency of 28 GHz and 13 GHz. These results have been obtained with an optimized transistor geometry to reduce the influence of the access resistances. The high-frequency potential of this 0.18-μm SOI technology demonstrates the possible integration of microwave functions with digital circuits on a single chip for low-power, low-voltage applications like wireless telecommunication     

1.3-μm continuous-wave lasing operation in GaInNAs quantum-welllasers

A 1.3-μm continuous wave lasing operation is demonstrated, for the first time, in a GaInNAs quantum-well laser at room temperature. This lasing performance is achieved by increasing the nitrogen content (up to 1%) in GaInNAs quantum layer. It is thus confirmed that this type of laser is suitable for use as a light source for optical fiber communications     

High-reliability 1.3-μm InP-based uncooled lasers in nonhermeticpackages

We report the first uncooled nonhermetic 1.3-μm InP-based communication lasers that have reliability comparable to their hermetically packaged counterparts for possible applications in fiber in the loop and cable TV. The development of reliable nonhermetic semiconductor lasers would not only lead to the elimination of the costs specifically associated with hermetic packaging but also lead the way for possible revolutionary low-cost optoelectronic packaging technologies. We have used Fabry-Perot capped mesa buried-heterostructure (CMBH) uncooled lasers with both bulk and MQW active regions grown on n-type InP substrates by VPE and MOCVD. We find that the proper dielectric facet passivation is the key to obtain high reliability in a nonhermetic environment. The passivation protects the laser from the ambient and maintains the proper facet reflectivity to achieve desired laser characteristics. The SiO facet passivation formed by molecular beam deposition (MBD) has resulted in lasers with lifetimes well in excess of the reliability goal of 3,000 hours of operation at 85°C/90% RH/30 mA aging condition. Based on extrapolations derived experimentally, we calculate a 15-year-average device hazard rate of <300 FITs (as against the desired 1,500 FITs) for the combination of thermal-and humidity-induced degradation at an ambient condition of 45°C/50% RH. For comparison, the average hazard rate at 45°C and 15 years of service is approximately 250 FITs for hermetic lasers of similar construction. A comparison of the thermal-only degradation (hermetic) to the thermal plus humidity-induced degradation (nonhermetic) indicates that the reliability of these nonhermetic lasers is controlled by thermal degradation only and not by moisture-induced degradation. In addition to device passivation for a nonhermetic environment, MBD-SiO maintains the optical, electrical, and mechanical properties needed for high-performance laser systems     

Monolithic integration of 1.3-μm Stark-ladder electroabsorptionwaveguide modulators with multimode-interference splitters

In this letter, we describe a novel fabrication process for the monolithic integration of a waveguide power splitter based on the multimode-interference effect with multiple-quantum well (MQW) electroabsorption modulators based on the Stark-ladder effect. The integrated device is fabricated by a one-step epitaxy process using molecular-beam-epitaxy growth and three lithographic steps that eliminates the need for aligned regrowth of the MQW modulator. Experimental results of the modulation depth and wavelength dependence are also reported     

Characteristics of 1.3-μm InGaAsP lasers used as photodetectors

The photodetection capabilities of 1.3-μm channel substrate lasers are studied. The diodes can be used either as lasers or detectors in single-mode-fiber half-duplex communication links. As a detector, a responsivity of 0.26 A/W is obtained by efficiently coupling the input radiation into the facet using a lensed single-mode fiber. The spectral bandwidth extends from 1.1 to 1.37 μm. The dark current at room temperature is 200 nA at 1-V bias and due in part to current leakage through the Fe-doped InP blocking layer. As lasers, the diodes have a frequency response of 4 GHz, and as detectors, the 3-dB bandwidth is 600 MHz     

Design criteria of 1.3-μm multiple-quantum-well lasers forhigh-temperature operation

We present design criteria for high-temperature operation in 1.3-μm multiple-quantum-well (MQW) lasers from the viewpoint of the light output power penalty, i.e., the change in the light output power at a fixed drive current with increasing temperature. It is shown that not only the characteristic temperature (T₀) but also internal loss dependence on temperature (γ) and threshold current (I_th) are significant parameters for reducing the power penalty. We compare the high-temperature performance of InGaAsP-based and AlGaInAs-based MQW lasers and demonstrate that AlGaInAs-based lasers have more potential in terms of the power penalty. Furthermore, we also demonstrate that the power penalty can be reduced by introducing a buried-heterostructure (BH) structure into AlGaInAs-based lasers. From these results, we conclude that the AlGaInAs-based BH lasers are promising for high-temperature performance     

1.3-μm CW lasing characteristics of self-assembled InGaAs-GaAsquantum dots

This paper presents the lasing properties and their temperature dependence for 1.3-μm semiconductor lasers involving self-assembled InGaAs-GaAs quantum dots as the active region. High-density 1.3-μm emission dots were successfully grown by the combination of low-rate growth and InGaAs-layer overgrowth using molecular beam epitaxy. 1.3-μm ground-level CW lasing occurring at a low threshold current of 5.4 mA at 25°C with a realistic cavity length of 300 μm and high-reflectivity coatings on both facets. The internal loss of the lasers was evaluated to be about 1.2 cm^-1 from the inclination of the plots between the external quantum efficiency and the cavity length. The ground-level modal gain per dot layer was evaluated to be 1.0 cm^-1, which closely agreed with the calculation taking into account the dot density, inhomogeneous broadening, and homogeneous broadening. The characteristic temperature of threshold currents T₀ was found to depend on cavity length and the number of dot layers in the active region of the lasers. A T₀ of 82 K was obtained near room temperature, and spontaneous emission intensity as a function of injection current indicated that the nonradiative channel degraded the temperature characteristics. A low-temperature study suggested that an infinite T₀ with a low threshold current (~1 mA) is available if the nonradiative recombination process is eliminated. The investigation in this paper asserted that the improvement in surface density and radiative efficiency of quantum dots is a key to the evolution of 1.3-μm quantum-dot lasers     

1.3-μm AlGaInAs-AlGaInAs strained multiple-quantum-well laserswith a p-AlInAs electron stopper layer

1.3-μm AlGaInAs-AlGaInAs strained multiple-quantum-well (MQW) lasers with a p-AlInAs electron stopper layer have been fabricated. The electron stopper layer was inserted between the MQW and p-side separate confinement heterostructure (SCH) layers to suppress the electron overflow from the MQW to p-SCH. The characteristic temperatures of the threshold currents and slope efficiencies were improved in the lasers with the stopper layers, especially at higher temperatures. As a result, a maximum operating temperature of 155°C was achieved, which was 20°C higher than that without the stopper layer     

Asymmetric output characteristics in 1.3-μm spot-size convertedlaser diodes

A spot-size converted laser diode (SSC-LD) with a vertically tapered passive waveguide structure was fabricated by butt-joint-built-in (BJB) coupling and selective area metal organic chemical vapor deposition growth. A high coupling efficiency exceeding 50% and 1-dB alignment tolerance of ±2.5 μm were obtained at a distance of 20 μm between a flat-end single-mode fiber and the SSC-LD. Experimental results show that the asymmetric output property can be described by the radiation mode added to the guide mode and spatial hole-burning in the active region