High-power/high-brightness diode-pumped 1.9-/spl mu/m thulium and resonantly pumped 2.1-/spl mu/m holmium lasers

We report high power (>36 W) with beam propagation factor M/sup 2//spl sim/2 in a diode end-pumped Tm:LiYF/sub 4/ (Tm:YLF) laser generating output near the 1.91-/spl mu/m region. Using the 1.91-/spl mu/m emission and high brightness achieved with the Tm:YLF laser we resonantly end-pump the Holmium /sup 5/I/sub 7/ manifold in Ho:YAG and demonstrate /spl sim/19 W of continuous-wave (CW) output. The diode-to-Holmium optical to-optical conversion efficiency achieved is /spl sim/18%. Using a CW pumped and repetitively Q-switched configuration, the Tm:YLF pumped Ho:YAG laser achieves >16 W of output power with an M/sup 2//spl sim/1.48 at 15 kHz. A Q-switched frequency range of 9 to >50 kHz is also achieved.     

Strain-compensated GaInNAs structures for 1.3-/spl mu/m lasers

GaAs-based dilute nitride lasers are potential light sources for future optical fiber communication systems at the wavelength of 1.3 /spl mu/m. In this paper we discuss the results of studies of optimization of the growth conditions and active regions of the GaAs-based lasers. To this end, a series of samples were grown using the molecular beam epitaxy technique. The active regions consisted of quantum wells, strain-compensating layers, and strain-mediating layers. They were characterized by photoluminescence and double crystal X-ray diffraction methods. The optical properties were very much affected by a choice of growth conditions, details of the quantum wells, and postgrowth thermal treatment. Preliminary results on diode-pumped vertical-cavity surface emitting lasers, which launch light power of 3.5 mW coupled into a single-mode fiber, are also presented.     

1.55-/spl mu/m bipolar cascade segmented ridge lasers

Scalable bipolar cascade lasers are achieved by electrically segmenting an InP ridge laser, and then series-connecting the segments. Lasers with up to 12 stages are demonstrated with record 390% continuous wave differential efficiency, and very low threshold currents. Three-stage lasers with 50-/spl Omega/ input impedance and over 100% differential efficiency are modulated with 2.5-GB/s digital data, and have 5-GHz analog modulation bandwidth. Noise and distortion properties are at least as good as single-stage control lasers.     

ESD-induced oxide breakdown on self-protecting GG-nMOSFET in 0.1-/spl mu/m CMOS technology

Historically, the failure mode of the nMOS/lateral n-p-n (L/sub npn/) bipolar junction transistor (BJT) due to electrostatic discharge (ESD) is source-to-drain filamentation, as the temperature exceeds the melting temperature of silicon. However, as the gate-oxide thickness shrinks, the ESD failure changes over to oxide breakdown. In this paper, transmission line pulse (TLP) testing is combined with measurements of various leakage currents and numerical simulations of the electric field to examine the failure mode of an advanced 0.1-/spl mu/m CMOS technology, which is shown to be through gate-oxide breakdown. It is also shown by I/sub D/-V/sub G/ and I/sub G/-V/sub G/ measurements that the application of nondestructive ESD pulses causes gradual degradation of the oxide well before failure is reached, under the (leakage current) failure criteria used. Finally, the latent effects of stress-induced oxide degradation on the failure current I/sub f/ of the nMOS/L/sub npn/ are studied, and it is shown that as the device ages from an oxide perspective, its ESD protection capabilities decrease.     

On the temperature sensitivity of 1.5-/spl mu/m GaInNAsSb lasers

We analyze the temperature sensitivity of 1.5-/spl mu/m GaInNAsSb lasers grown on GaAs. Building on the method of Tansu and coworkers, we find evidence that the characteristic temperatures for the threshold current T/sub 0/ and external efficiency T/sub 1/ are balanced by a combination of monomolecular recombination and temperature destabilizing mechanism(s) near room temperature. At elevated temperatures, the destabilizing process(es) dominate, due to increased threshold current density J/sub th/. While it is difficult to definitively identify carrier leakage, Auger recombination, or a combination of the two as the responsible mechanism(s), results indicate that carrier leakage certainly plays a role. Evidence of intervalence band absorption was also found; T/sub 1/ was reduced, but J/sub th/ and T/sub 0/ were not significantly degraded. Conclusions are corroborated by supporting measurements of the Z-parameter with bias, spontaneous emission spectrum, and band-offsets. Spontaneous emission measurements show evidence of weak Fermi-level pinning within the active region at threshold, indicating a form of carrier leakage. This is consistent with the characteristic temperature analysis and a leakage mechanism is proposed. This process is partially responsible for the greater temperature sensitivity of device parameters and the poor internal efficiency. Methods for reducing the effects of each parasitic mechanism are also described.     

Theoretical and experimental analysis of 1.3-/spl mu/m InGaAsN/GaAs lasers

We present a comprehensive theoretical and experimental analysis of 1.3-/spl mu/m InGaAsN/GaAs lasers. After introducing the 10-band k /spl middot/ p Hamiltonian which predicts transition energies observed experimentally, we employ it to investigate laser properties of ideal and real InGaAsN/GaAs laser devices. Our calculations show that the addition of N reduces the peak gain and differential gain at fixed carrier density, although the gain saturation value and the peak gain as a function of radiative current density are largely unchanged due to the incorporation of N. The gain characteristics are optimized by including the minimum amount of nitrogen necessary to prevent strain relaxation at the given well thickness. The measured spontaneous emission and gain characteristics of real devices are well described by the theoretical model. Our analysis shows that the threshold current is dominated by nonradiative, defect-related recombination. Elimination of these losses would enable laser characteristics comparable with the best InGaAsP/InP-based lasers with the added advantages provided by the GaAs system that are important for vertical integration.     

High-pressure studies of recombination mechanisms in 1.3-/spl mu/m GaInNAs quantum-well lasers

The pressure dependence of the components of the recombination current at threshold in 1.3-/spl mu/m GaInNAs single quantum-well lasers is presented using for the first time high-pressure spontaneous emission measurements up to 13 kbar. It is shown that, above 6 kbar, the rapid increase of the threshold current with increasing pressure is associated with the unusual increase of the Auger-related nonradiative recombination current, while the defect-related monomolecular nonradiative recombination current is almost constant. Theoretical calculations show that the increase of the Auger current can be attributed to a large increase in the threshold carrier density with pressure, which is mainly due to the increase in the electron effective mass arising from the enhanced level-anticrossing between the GaInNAs conduction band and the nitrogen level.     

Recombination and loss mechanisms in low-threshold InAs-GaAs 1.3-/spl mu/m quantum-dot lasers

We show that even in quantum-dot (QD) lasers with very low threshold current densities (J/sub th/=40--50 A/cm/sup 2/ at 300 K), the temperature sensitivity of the threshold current arises from nonradiative recombination that comprises /spl sim/60% to 70% of J/sub th/ at 300 K, whereas the radiative part of J/sub th/ is almost temperature insensitive. The influence of the nonradiative recombination mechanism decreases with increasing hydrostatic pressure and increasing band gap, which leads to a decrease of the threshold current. We also studied, for the first time, the band gap dependence of the radiative part of J/sub th/, which in contrast increases strongly with increasing band gap. These results suggest that Auger recombination is an important intrinsic recombination mechanism for 1.3-/spl mu/m lasers, even in a very low threshold QD device, and that it is responsible for the temperature sensitivity of the threshold current.     

1.5-/spl mu/m wavelength narrow stripe distributed reflector lasers for high-performance operation

1.5 /spl mu/m-wavelength narrow stripe distributed reflector (DR) lasers consisting of first-order vertical grating (VG) and distributed Bragg reflector (DBR) mirrors were realized by deeply etching the as-grown wafer and passivating the etched surface by SiO/sub 2/. Design consideration, fabrication, and lasing performances were studied. A low threshold current of 2.8 mA and a differential quantum efficiency of 28% from the front facet were achieved for a 1.3 /spl mu/m stripe width and a 150 /spl mu/m cavity length under room temperature (RT) continuous wave (CW) operation. Details of threshold behavior of these lasers are presented. Lasing performances of FP and DBR lasers are also described for comparison.     

0.5-/spl mu/m CMOS orthogonal encoding readout cell for active imaging systems

We propose a novel continuous-time simultaneous-readout scheme for active imaging systems based on orthogonal modulation of photodetector signals. The superimposed-continuous-time approach presented here differs from the conventional scheduled-discrete-time scheme in that the photodetector signals are summed in a common bus and read concurrently. We show how that our proposed architecture may be advantageous, particularly in applications where bandwidth requirements for a time-multiplexed scheme are highly demanding. The active readout cell presented here is the kernel of the proposed orthogonal encoding architecture. We describe the cell operation principle, its properties and major design challenges. A 0.5-/spl mu/m CMOS test chip has been fabricated to demonstrate functionality of the readout architecture. Test results show it to be a viable option for highly-integrated active imaging systems.     

Differential gain and linewidth-enhancement factor in dilute-nitride GaAs-based 1.3-/spl mu/m diode lasers

The effect of the quantum-well nitride content on the differential gain and linewidth enhancement factor of dilute-nitride GaAs-based near 1.3-/spl mu/m lasers was studied. Gain-guided and ridge waveguide lasers with 0%, 0.5%, and 0.8% nitrogen content InGaAsN quantum wells were characterized. Experiment shows that the linewidth enhancement factor is independent on the nitride content, and is in the range 1.7-2.5 for /spl lambda/=1.22--1.34 /spl mu/m dilute-nitride GaAs-based lasers. Differential gain and index with respect to either current or carrier concentration are reduced in dilute-nitride devices.     

A 0.18 /spl mu/m CMOS pipelined encoder for a 5 GS/s 4-bit flash analogue-to-digital converter

A high-speed CMOS encoder intended for a 5 gigasample/second (GS/s) 4-bit flash analogue-to-digital converter (ADC) is presented. To meet the speed and power targets of the ADC, low-swing signalling is used in all the internal sub-blocks of the ADC, including the encoder, which is implemented in current-mode logic (CML). To further enhance the encoders speed, two-stage pipelining is used. Details of the architecture are described. The proposed two-stage pipelined encoder as well as an encoder with no pipelining are designed and simulated in a 0.18 μm CMOS technology, and their performances are compared. Simulation results predict a 40% speed improvement for the pipelined encoder. The encoder circuit consumes 4 mW from a 1.8 V supply while operating at 5 GHz.     

Design consideration and performance of high-power and high-brightness InGaAs-InGaAsP-AlGaAs quantum-well diode lasers (/spl lambda/=0.98 /spl mu/m)

We conduct a theoretical analysis of the design, fabrication, and performance measurement of high-power and high-brightness strained quantum-well lasers emitting at 0.98 /spl mu/m. The material system of interest consists of an Al-free InGaAs-InGaAsP active region and AlGaAs cladding layers. Some key parameters of the laser structure are theoretically analyzed, and their effects on the laser performance are discussed. The laser material is grown by metal-organic chemical vapor deposition and demonstrates high quality with low-threshold current density, high internal quantum efficiency, and extremely low internal loss. High-performance broad-area multimode and ridge-waveguide single-mode laser devices are fabricated. For 100-/spl mu/m-wide stripe lasers having a cavity length of 800 /spl mu/m, a high slope efficiency of 1.08 W-A, a low vertical beam divergence of 34/spl deg/, a high output power of over 4.45 W, and a very high characteristic temperature coefficient of 250 K were achieved. Lifetime tests performed at 1.2-1.3 W (12-13 mW//spl mu/m) demonstrates reliable performance. For 4-/spl mu/m-wide ridge waveguide single-mode laser devices, a maximum output power of 394 mW and fundamental mode power up to 200 mW with slope efficiency of 0.91 mW//spl mu/m are obtained.     

1.30-/spl mu/m GaInNAs laser diode with lifetime over 1000 hours grown by MOCVD

We performed epitaxial growth of GaInNAs laser diodes under various growth rates by metal-organic chemical vapor deposition. A strong correlation was found between the growth rate and the photoluminescence (PL) characteristics. At the optimum growth rate, PL peak intensity and full-width at half-maximum of the PL peak were at a maximum and minimum, respectively. As a result of processing on a GaInNAs narrow-ridge waveguide laser device, a strong correlation was found between the growth rate and the device characteristics. At the optimum growth rate, which was the same optimum growth rate for the PL characteristics, the threshold current and characteristic temperature were also at their optimum values. It is clear that the growth rate is an important parameter for crystal quality and device characteristics. As a result of the optimization of the growth rate and the other growth conditions, a high characteristic temperature of 180 K and a long device lifetime over 1000 h were obtained.     

ESD failure mechanisms of analog I/O cells in 0.18-/spl mu/m CMOS technology

Different electrostatic discharge (ESD) protection schemes have been investigated to find the optimal ESD protection design for an analog input/output (I/O) buffer in 0.18-/spl mu/m 1.8- and 3.3-V CMOS technology. Three power-rail ESD clamp devices were used in power-rail ESD clamp circuits to compare the protection efficiency in analog I/O applications, namely: 1) gate-driven NMOS; 2) substrate-triggered field-oxide device, and 3) substrate-triggered NMOS with dummy gate. From the experimental results, the pure-diode ESD protection devices and the power-rail ESD clamp circuit with gate-driven NMOS are the suitable designs for the analog I/O buffer in the 0.18-/spl mu/m CMOS process. Each ESD failure mechanism was inspected by scanning electron microscopy photograph in all the analog I/O pins. An unexpected failure mechanism was found in the analog I/O pins with pure-diode ESD protection design under ND-mode ESD stress. The parasitic n-p-n bipolar transistor between the ESD clamp device and the guard ring structure was triggered to discharge the ESD current and cause damage under ND-mode ESD stress.     

1.3-/spl mu/m AlGaInAs strain compensated MQW-buried-heterostructure lasers for uncooled 10-gb/s operation

We have successfully fabricated 1.3-/spl mu/m AlGaInAs strain-compensated multiple-quantum-well (MQW) buried-heterostructure (BH) lasers by narrow-stripe selective metalorganic vapor-phase epitaxy. Based on the optimization of AlGaInAs strain compensated MQW and the Al-oxidation-free BH process, we obtained a low-threshold current of 12.5 mA and a relaxation frequency of more than 10 GHz at 85/spl deg/C for Fabry-Perot lasers. For distributed feedback lasers, we demonstrated a 10-Gb/s operation and transmission of over 16 Km for a single mode fiber at 100/spl deg/C. Furthermore, a record-low 25.8-mA/sub p-p/ modulation current for a 10-Gb/s modulation at 100/spl deg/C was demonstrated with shorter cavity and high grating-coupling coefficient. A median life of more than 1/spl times/10/sup 5/ h at 85/spl deg/C was estimated after an aging test of over 5000 h for these lasers. These superior characteristics at high temperatures were achieved by the combination of the high differential gain of AlGaInAs strain compensated MQW and the BH structure.     

Single-mode 1.27-/spl mu/m InGaAs:Sb-GaAs-GaAsP quantum well vertical cavity surface emitting lasers

The 1.27-/spl mu/m InGaAs:Sb-GaAs-GaAsP vertical cavity surface emitting lasers (VCSELs) were grown by metalorganic chemical vapor deposition and exhibited excellent performance and temperature stability. The threshold current varies from 1.8 to 1.1 mA and the slope efficiency falls less than /spl sim/35% from 0.17 to 0.11 mW/mA as the temperature is raised from room temperature to 75/spl deg/C. The VCSELs continuously operate up to 105/spl deg/C with a slope efficiency of 0.023 mW/mA. With a bias current of only 5 mA, the 3-dB modulation frequency response was measured to be 8.36 GHz, which is appropriate for 10-Gb/s operation. The maximal bandwidth is estimated to be 10.7 GHz with modulation current efficiency factor of /spl sim/5.25GHz/(mA)/sup 1/2/. These VCSELs also demonstrate high-speed modulation up to 10 Gb/s from 25/spl deg/C to 70/spl deg/C. We also accumulated life test data up to 1000 h at 70/spl deg/C/10 mA.     

GaAs-based modulation-doped quantum-well infrared photodetectors for single- and two-color detection in 3-5 /spl mu/m

Double-barrier quantum-well infrared photodetectors are promising for operation in the midinfrared region. In this paper, we present a series of novel molecular beam epitaxy (MBE)-grown devices based on modulation-doped (MD) AlGaAs-AlAs-GaAs structures that exhibit a remarkable responsivity at zero bias (0.05 A/W) at 4.6 /spl mu/m. Since the photovoltaic properties are strongly dependent on the symmetry of the potential profile, we have systematically varied the position of the dopant in the barriers for a series of single-color detectors. Low-temperature photocurrent spectra and current-voltage (I-V) characteristics (in the dark and under illumination) show that the location of the dopant is a relevant design parameter, due to its role in the photovoltaic behavior (i.e., the presence or absence of zero bias signal). The performance of the MD devices is compared with that of a detector with doping in the center of the well and otherwise the same structure. In particular, the responsivity and detectivity seem to be higher for the MD detectors than for well-doped samples, especially when the dopant is located in the barrier closest to the substrate. Therefore, we have chosen that MD dopant profile when designing and growing, to our knowledge, the first 3-5 /spl mu/m two-color detector, with simultaneous detection at 3.8 and 4.4 /spl mu/m.     

Cavity enhancement of Auger-suppressed detectors: a way to background-limited room-temperature operation in 3-14-/spl mu/m range

We consider the combination of nonequilibrium Auger suppression with cavity enhancement, this being either resonant cavity enhancement (RCE) or photonic crystal enhancement (PCE) as a means to suppress generation-recombination processes in intrinsic semiconductor-based long wavelength infrared detectors. The aim is to approach the background-limited operation of narrow-bandgap compound semiconductor photodetectors in the 3-14 /spl mu/m infrared wavelength range without cooling or possibly with slight cooling. Auger generation-recombination processes are suppressed utilizing exclusion, extraction, magnetoconcentration, or some of their combinations. The residual radiative recombination is removed by enclosing the detector active area into a cavity with a radiative shield (resonant cavity or photonic crystal) and using the benefits of reabsorption (photon recycling) to effectively increase radiative lifetime.