alpha factor improvements in high-speed p doped In/sub 0.35/Ga /sub 0.65/As/GaAs MQW lasers

The authors investigate experimentally for the first time the improvements in the linewidth enhancement factor, alpha , resulting from simultaneous addition of strain and p-doping in high-speed GaAs-based multiquantum well lasers. The alpha factor is determined from measured changes in both gain and refractive index as a function of CW bias current, yielding alpha 3.1 and 1.4 at the threshold lasing wavelength for unstrained GaAs/Al/sub 0.25/Ga/sub 0.75/As and p-doped strained In/sub 0.35/Ga/sub 0.65/As/GaAs devices, respectively.<>     

Carrier dynamics in high-speed (f/sub -3 dB/>40 GHz) 0.98-/spl mu/m multiquantum-well tunneling injection lasers determined from electrical impedance measurements

Carrier capture times in InGaAs-AlAs-GaAs 0.98-/spl mu/m multiquantum-well tunneling injection lasers with f/sub -3 dB//spl sim/43-48 GHz have been determined from analysis of high frequency electrical impedance measurements. The capture times range from 14 ps, at biases around threshold, to about 1 ps, at 50-mA bias. The small capture times agree well with tunneling times obtained directly from pump-probe measurements. The impedance measurements also suggest that the carrier lifetime in the well is much less than the escape time from the well, consistent with the cold carrier distribution associated with a tunneling injection mechanism.     

Impedance characteristics of quantum-well lasers

We derive theoretical expressions for the impedance of quantum-well lasers below and above threshold based on a simple rate equation model. These electrical laser characteristics are shown to be dominated by purely electrical parameters related to carrier capture/transport and carrier re-emission. The results of on-wafer measurements of the impedance of high-speed In_0.35Ga_0.65 As/GaAs multiple-quantum-well lasers are shown to be in good agreement with this simple model, allowing us to extract the effective carrier escape time and the effective carrier lifetime, and to estimate the effective carrier capture/transport time     

Carrier dynamics and microwave characteristics of GaAs-basedquantum-well lasers

We investigate the effects of carrier capture and re-emission on the electrical impedance, equivalent circuit, and modulation response of quantum-well (QW) laser diodes. The electrical impedance is shown to be a sensitive function of the time constants associated with carrier capture/transport and carrier re-emission. We compare the theoretical results with measured values of the electrical impedance of high-speed InGaAs-GaAs multiple-quantum-well lasers fabricated using different epilayer structures with a common lateral structure. The experimental results agree well with the theoretical model, allowing us to extract the effective carrier escape time and the effective carrier lifetime in the QWs, and to estimate the effective carrier capture/transport time     

Carrier DC and AC capture and escape times in quantum-well lasers

A theoretical model is proposed to study the carrier DC and AC capture and escape times in the small signal modulation response of quantum-well lasers. We derive the DC and AC capture and escape times by calculating the carrier net capture current. Our numerical results indicate that the AC capture and escape times are smaller than the DC capture and escape times. In some cases, they may be even smaller by one order of magnitude. We also find that the AC capture/escape time ratio is larger than the DC capture/escape time ratio by a factor of two. Therefore, conventional theoretical models that do not distinguish the differences between the DC and AC capture and escape times may overestimate the resonant frequency and underestimate the damping rate in the modulation response of quantum-well lasers, i.e., the AC capture and escape times limit the modulation bandwidth of quantum-well lasers more severely than that predicted by the DC capture and escape times     

Impedance, modulation response, and equivalent circuit ofultra-high-speed In0.35Ga0.65As/GaAs MQW laserswith p-doping

On-wafer measurements of the frequency-dependent impedance, modulation response, and RIN power spectra of ultra-high-speed p-doped In_0.35Ga_0.65As/GaAs MQW lasers are presented and analyzed. The experimental results are shown to be accurately modeled by an equivalent circuit which accounts for both the carrier transport/capture dynamics and the junction space-charge capacitance. We find that the carrier escape time out of the QW's in our laser structure is much larger. Than the carrier capture time, and therefore the interplay between carrier capture and re-emission is not affecting the high-speed modulation dynamics. On the other hand, the absolute values of both the carrier capture time and the space-charge capacitance still limit the modulation bandwidth     

InGaAsP-InP nanoscale waveguide-coupled microring lasers with submilliampere threshold current using Cl/sub 2/--N/sub 2/-based high-density plasma etching

We demonstrate InGaAsP-InP nanoscale waveguide-coupled microring lasers fabricated with inductively coupled plasma (ICP) using Cl/sub 2/--N/sub 2/-based gas mixtures. To fabricate optical waveguides, the requirement of anisotropic profiles and sidewall smoothness is stringent. In particular, for strongly lateral confined nanoscale waveguides used for microring resonators, the degree of anisotropy and sidewall smoothness is critical in determining the device performance. For optoelectronic devices such as microcylinder and microring lasers, the requirement of low active-layer damage further adds to the stringency. We show that the excellent etching property of high-density plasma using Cl/sub 2/--N/sub 2/-based gas mixtures satisfies the requirements. The good etching results are demonstrated by using the etching method to realize room-temperature operations of the InGaAsP-InP waveguide-coupled microring lasers. For the waveguide-coupled microring lasers with a diameter of 10 /spl mu/m, we obtained submilliampere threshold current.     

Refractive index step and optical confinement in Ga/sub 0.86/In/sub 0.14/As/sub 0.13/Sb/sub 0.87//Ga/sub 0.73/Al/sub 0.27/As/sub 0.02/Sb/sub 0.98/ double heterostructure lasers emitting at 2.2 mu m

Using theoretical fitting to measured transverse far field patterns in Ga/sub 0.86/In/sub 0.14/As/sub 0.13/Sb/sub 0.87//Ga/sub 0.73/Al/sub 0.27/As/sub 0.02/Sb/sub 0.98/ DH lasers emitting at 2.2 mu m the authors estimated the value of the active layer refractive index as 3.78. This value, higher than assumed earlier based on theoretical calculations, ensures good optical confinement for this kind of heterostructure and provides a good theoretical fit with the authors' experimental data of threshold current density against active layer thickness.<>     

Lasing at three-dimensionally quantum-confined sublevel of self-organized In/sub 0.5/Ga/sub 0.5/As quantum dots by current injection

A laser oscillation from self-organized In/sub 0.5/Ga/sub 0.5/As quantum dots is achieved at 80 K by current injection. Lasing at a three-dimensionally quantum confined sublevel of the In/sub 0.5/Ga/sub 0.5/As quantum dots is clearly demonstrated for the first time by electroluminescence and diamagnetic energy shift measurement. The results predict the possibility of ultra-low threshold current operation of quantum dot lasers.     

Room-temperature self-organised In/sub 0.5/Ga/sub 0.5/As quantum dot laser on silicon

The first room-temperature operation of In/sub 0.5/Ga/sub 0.5/As quantum dot lasers grown directly on Si substrates with a thin (/spl les/2 /spl mu/m) GaAs buffer layer is reported. The devices are characterised by J/sub th//spl sim/1500 A/cm/sup 2/, output power >50 mW, and large T/sub 0/ (244 K) and constant output slope efficiency (/spl ges/0.3 W/A) in the temperature range 5-95/spl deg/C.     

Band diagram and carrier conduction mechanisms in ZrO/sub 2/ MIS structures

Energy-band diagrams and carrier-conduction mechanisms in ZrO/sub 2/ dielectrics were investigated by using X-ray photoemission spectroscopy and carrier separation measurements for ZrO/sub 2/ /Zr-silicate/Si structures. It was found that the carrier conduction mechanisms in ZrO/sub 2/ layer dominate the leakage current in the ZrO/sub 2/ /Zr-silicate/Si-stacked structure. Furthermore, it was found that the dominant electron conduction mechanism in ZrO/sub 2/ dielectrics is a Poole-Frenkel (P-F) conduction and that the dominant hole conduction mechanism in ZrO/sub 2/ dielectrics is a Fowler-Nordheim conduction. On the basis of the understanding of these carrier conduction mechanisms, it was indicated that the leakage current density in the dielectrics with the P-F conduction mechanism having the small barrier height of 0.8 eV could not be reduced below 1 A/cm/sup 2/ at the operation voltage of 1 V. Furthermore, we suggest that the ultrathin Zr-silicate single layer is a promising candidate gate dielectric material for advanced MISFET having 1-nm effective thickness.     

Carrier capture and escape processes inIn0.25Ga0.75As-GaAs quantum-well lasers

We have extracted the ratio between the carrier capture and escape times, η, for In_0.25Ga_0.75As-GaAs lasers containing one, two, or three quantum wells, from high-frequency subthreshold impedance measurements at different temperatures. Our results show that the carrier capture process dominates over the diffusion along the confinement region in the overall transport/capture process. The obtained value for η is comparable to unity, and this fact has to be taken into account to obtain real material parameters, such as the carrier lifetime and the radiative recombination coefficient     

Tunable Q-switched/cavity-dumped Z-fold CO/sub 2/ waveguide laser with two channels and common electrodes

A tunable Q-switched/cavity-dumped z-fold CO/sub 2/ waveguide laser with two channels and common electrodes is studied. The Q-switched and cavity-dumped pulse lasers have been obtained from the z-fold channel with the tunable pulse repetition frequency (PRF) of 1-70 kHz. At the Q-switched operation, the peak power is 730 W and the pulsewidth is 150 ns at the PRF of 10 KHz. At the cavity-dumped operation, the pulse laser width can be adjusted. The peak power is 6000 W with the pulsewidth of 20 ns and 3400 W for 32 ns. CW laser output has been obtained from the other channel and its frequency can be tuned by a piezoelectric transducer. The Q-switched and cavity-dumped pulse laser heterodyne waveforms are observed.     

(InAs)/sub 1//(GaAs)/sub 4/ superlattice strained quantum well laser at 980 nm

The first successful MBE growth of (InAs)/sub 1//(GaAs)/sub 4/ short-period superlattice (SPS) strained quantum well lasers emitting at approximately 980 nm is reported. The SPS consists of six periods of one and four monolayers of InAs and GaAs, respectively. The measured threshold current density was approximately 100 A cm/sup -2/ for 0.96 mm long lasers. Devices have operated up to 170 degrees C with a characteristic temperature T/sub 0/ of 148 K. The (InAs)/sub m//(GaAs)/sub n/ superlattice is an ordered counterpart of the InGaAs random alloy, and provides an alternative method fabricating high speed electronic and photonic devices.<>     

Effect of Mg doping on the superconducting properties of Cu/sub 1-x/Tl/sub x/Ba/sub 2/Ca/sub 3-y/Mg/sub y/Cu/sub 4/O/sub 12-/spl delta//

Superconducting properties of Cu/sub 1-x/Tl/sub x/Ba/sub 2/Ca/sub 3-y/Mg/sub y/Cu/sub 4/O/sub 12-/spl delta// (Cu/sub 1-x/Tl/sub x/Mg/sub y/-1234) material have been studied in the composition range y=0,1.5,2.25. The zero resistivity critical temperature [T/sub c/(R=0)] was found to increase with the increased concentration of Mg in the unit cell; for y=1.5 [T/sub c/(R=0)]=131 K was achieved which is hitherto highest in Cu/sub 1-x/Tl/sub x/-based superconductors. The X-ray diffraction analyses have shown the formation of a predominant single phase of Cu/sub 0.5/Tl/sub 0.5/Ba/sub 2/Ca/sub 3-y/Mg/sub y/Cu/sub 4/O/sub 12-/spl delta// superconductor with an inclusion of impurity phase. It is observed from the convex shape of the resistivity versus temperature measurements that our as-prepared material was in the region of carrier over-doping, and the number of carriers was optimized by postannealing experiments in air at 400/spl deg/C, 500/spl deg/C, and 600/spl deg/C. The T/sub c/(R=0) was found to increase with postannealing and the best postannealing temperature was found to be 600/spl deg/C. The mechanism of increased T/sub c/(R=0) is understood by carrying out infrared absorption measurements. It was observed through softening of Cu(2)-O/sub A/-Tl apical oxygen mode that improved interplane coupling was a possible source of enhancement of T/sub c/(R=0) to 131 K.     

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.     

A novel strained Si/sub 0.7/Ge/sub 0.3/ surface-channel pMOSFET with an ALD TiN/Al/sub 2/O/sub 3//HfAlO/sub x//Al/sub 2/O/sub 3/ gate stack

Proof-of-concept pMOSFETs with a strained-Si/sub 0.7/Ge/sub 0.3/ surface-channel deposited by selective epitaxy and a TiN/Al/sub 2/O/sub 3//HfAlO/sub x//Al/sub 2/O/sub 3/ gate stack grown by atomic layer chemical vapor deposition (ALD) techniques were fabricated. The Si/sub 0.7/Ge/sub 0.3/ pMOSFETs exhibited more than 30% higher current drive and peak transconductance than reference Si pMOSFETs with the same gate stack. The effective mobility for the Si reference coincided with the universal hole mobility curve for Si. The presence of a relatively low density of interface states, determined as 3.3 /spl times/ 10/sup 11/ cm/sup -2/ eV/sup -1/, yielded a subthreshold slope of 75 mV/dec. for the Si reference. For the Si/sub 0.7/Ge/sub 0.3/ pMOSFETs, these values were 1.6 /spl times/ 10/sup 12/ cm/sup -2/ eV/sup -1/ and 110 mV/dec., respectively.     

Resistance-switching Characteristics of polycrystalline Nb/sub 2/O/sub 5/ for nonvolatile memory application

The resistance switching characteristics of polycrystalline Nb/sub 2/O/sub 5/ film prepared by pulsed-laser deposition (PLD) were investigated for nonvolatile memory application. Reversible resistance-switching behavior from a high resistance state to a lower state was observed by voltage stress with current compliance. The reproducible resistance-switching cycles were observed and the resistance ratio was as high as 50-100 times. The resistance switching was observed under voltage pulse as short as 10 ns. The estimated retention lifetime at 85/spl deg/C was sufficiently longer than ten years. Considering its excellent electrical and reliability characteristics, Nb/sub 2/O/sub 5/ shows strong promise for future nonvolatile memory applications.     

Damage induced in p-GaAs due to RIE in CH/sub 4//H/sub 2/ mixture

Damaged induced in p-GaAs due to RIE in pure H/sub 2/ and a mixture of CH/sub 4//H/sub 2/ has been investigated by I-V and C-V measurements on Au/p-GaAs Schottky diodes fabricated following the RIE process. The ideality factor, barrier height, depletion width and carrier concentration of the etched samples were compared with those of a control sample. Considerable eradication of induced damage was observed for the sample which was etched in CH/sub 4//H/sub 2/ mixture and was annealed prior to diode fabrication.<>     

Electrooptic ferroelectric Na/sub 0.5/K/sub 0.5/NbO/sub 3/ films

We report on waveguiding and electrooptic properties of epitaxial Na/sub 0.5/K/sub 0.5/NbO/sub 3/ films grown by radio-frequency magnetron sputtering on Al/sub 2/O/sub 3/(11_02) single crystal substrates. High optical waveguiding performance has been demonstrated in infrared and visible light. The in-plane electrooptic effect has been recorded in transmission using a transverse geometry. At dc fields, the effective linear electrooptic coefficient was determined to 28 pm/V, which is promising for modulator applications.