Low-temperature MBE-grown In/sub 0.52/Ga/sub 0.18/Al/sub 0.30/As/InP optical waveguides

The MBE growth of In/sub 0.52/Ga/sub 0.18/Al/sub 0.30/As ( lambda /sub g/=1.06 mu m) layers in the temperature range of 400-450 degrees C was demonstrated to give high-quality optical waveguides which not only exhibit low propagation losses as low as 0.5 dB/cm at lambda =1.55 mu m but concomitantly high resistivity of >10/sup 4/ Omega cm. The refractive index of In/sub 0.52/Ga/sub 0.18/Al/sub 0.30/As was estimated to be 3.207+or-0.03 at lambda =1.55 mu m.<>     

Experimental determination of carrier-induced differential loss in 2-section GaInAsP/InP laser-waveguide

Measurements of threshold current density and external efficiency on broad-area laser-waveguide structure have led to the determination of the optical loss and differential loss d alpha /dN approximately=1.1-2.3 *10/sup -17/ cm/sup 2/ at lambda =1.53 mu m in a lambda /sub g/=1.30 mu m GaInAsP layer. This measurement will be useful for the design of tunable lasers.<>     

Thickness dependence of Weibull slopes of HfO/sub 2/ gate dielectrics

Breakdown voltage distribution, Weibull slopes, and area scaling factors have been investigated for HfO/sub 2/ gate dielectrics in order to gain a better understanding of the breakdown mechanism. Weibull slope of thick HfO/sub 2/ (e.g., /spl beta//spl ap/4 for EOT=2.5 nm) is smaller than that of SiO/sub 2/ with similar physical thickness, whereas /spl beta/ of the thinner HfO/sub 2/ (e.g., /spl beta//spl ap/2 for EOT=1.4 nm) is similar to that of SiO/sub 2/. The implication of the thickness dependence of /spl beta/ is discussed.     

Low dark current quasi-Schottky barrier MSM-photodiode structures on n-Ga/sub 0.47/In/sub 0.53/As with p/sup +/-Ga/sub 0.47/In/sub 0.53/As cap layer

The p/sup +/-cap layer was used to fabricate a metal-semiconductor-metal (MSM) interdigitated photodetector on Ga/sub 0.47/In/sub 0.53/As. The measured barrier height was Phi /sub Bn=/0.52 V, the ideality factor n=1.1 and average dark current density 2 mA/cm/sup 2/. A rise time of 45 ps at lambda =1.3 mu m under 2 V bias was measured for an MSM photodiode with 3 mu m finger width and finger gaps and an active area of 100*100 mu m/sup 2/.<>     

Continuous-wave operation up to 36/spl deg/C of 1.3-/spl mu/m GaInAsP-InP vertical-cavity surface-emitting lasers

We introduced ion-beam assisted deposition in order to improve the quality of Al/sub 2/O/sub 3/ and SiO/sub 2/, which were used as part of the mirrors of 1.3-/spl mu/m GaInAsP-InP vertical-cavity surface-emitting lasers (VCSELs). The refractive index of Al/sub 2/O/sub 3/ was improved to 1.63 from 1.56 and the one of SiO/sub 2/ increased to 1.47 from 1.45. Low-threshold room-temperature continuous-wave (CW) operation of 1.3-/spl mu/m VCSEL with the improved mirrors was demonstrated. The threshold current was 2.4 mA at 20/spl deg/C. The CW operating temperature was raised to 36/spl deg/C, which is a record high temperature for 1.3-/spl mu/m VCSEL.     

Optical-pumping injection cavity (OPIC) mid-IR "W" lasers with high efficiency and low loss

We report an edge-emitting mid-infrared (IR) (/spl lambda/=3.3-3.7 /spl mu/m) "W" laser incorporating an optical-pumping injection cavity (OPIC). The active region of the W-OPIC is sandwiched between two Bragg mirrors that significantly enhance the pump-beam absorptance at /spl lambda//sub pump/=2.098 /spl mu/m. Pulsed experiments demonstrate that besides suppressing the threshold pump intensity, this design enhances the differential power conversion efficiency (e.g., 7.1% per uncoated facet at 220 K) and lowers the internal loss (e.g., 20 cm/sup -1/ at 240 K) compared with all previous optically pumped mid-IR lasers.     

Characteristics of MOSFET Prepared on Si/MgO /spl dot/ Al/sub 2/O/sub 3//SiO/sub 2//Si Structure

A new silicon on insulator (SOI) wafer with epitaxial-Si/ epitaxial-MgO/spl dot/Al/sub 2/O/sub 3/ (0.1 /spl mu/m)/SiO/sub 2/(0.5 /spl mu/m)/     

Continuous-wave erbium-diffused LiNbO/sub 3/ waveguide laser

The first integrated optical laser in LiNbO/sub 3/, doped by an indiffusion of Er/sup 3+/ prior to channel-guide fabrication by Ti diffusion is reported. Pumped by a colour centre ( lambda /sub p/=1.477 mu m), CW operation at lambda =1.532 mu m ( Delta lambda approximately 0.3 nm) with a threshold of approximately 8 mW absorbed power was achieved.<>     

G/sub m/-boosted common-gate LNA and differential colpitts VCO/QVCO in 0.18-/spl mu/m CMOS

The demand for radio frequency (RF) integrated circuits with reduced power consumption is growing owing to the trend toward system-on-a-chip (SoC) implementations in deep-sub-micron CMOS technologies. The concomitant need for high performance imposes additional challenges for circuit designers. In this paper, a g/sub m/-boosted common-gate low-noise amplifier (CGLNA), differential Colpitts voltage-controlled oscillators (VCO), and a quadrature Colpitts voltage-controlled oscillator (QVCO) are presented as alternatives to the conventional common-source LNA and cross-coupled VCO/QVCO topologies. Specifically, a g/sub m/-boosted common-gate LNA loosens the link between noise factor (i.e., noise match) and input matching (i.e., power match ); consequently, both noise factor and bias current are simultaneously reduced. A transformer-coupled CGLNA is described. Suggested by the functional and topological similarities between amplifiers and oscillators, differential Colpitts VCO and QVCO circuits are presented that relax the start-up requirements and improve both close-in and far-out phase noise compared to conventional Colpitts configurations. Experimental results from a 0.18-/spl mu/m CMOS process validate the g/sub m/-boosting design principle.     

Physically based quantum-mechanical compact model of MOS devices substrate-injected tunneling current through ultrathin (EOT /spl sim/ 1 nm) SiO/sub 2/ and high-/spl kappa/ gate stacks

Building on a previously presented compact gate capacitance (C/sub g/-V/sub g/) model, a computationally efficient and accurate physically based compact model of gate substrate-injected tunneling current (I/sub g/-V/sub g/) is provided for both ultrathin SiO/sub 2/ and high-dielectric constant (high-/spl kappa/) gate stacks of equivalent oxide thickness (EOT) down to /spl sim/ 1 nm. Direct and Fowler-Nordheim tunneling from multiple discrete subbands in the strong inversion layer are addressed. Subband energies in the presence of wave function penetration into the gate dielectric, charge distributions among the subbands subject to Fermi-Dirac statistics, and the barrier potential are provided from the compact C/sub g/-V/sub g/ model. A modified version of the conventional Wentzel-Kramer-Brillouin approximation allows for the effects of the abrupt material interfaces and nonparabolicities in complex band structures of the individual dielectrics on the tunneling current. This compact model produces simulation results comparable to those obtained via computationally intense self-consistent Poisson-Schro/spl uml/dinger simulators with the same MOS devices structures and material parameters for 1-nm EOTs of SiO/sub 2/ and high-/spl kappa//SiO/sub 2/ gate stacks on (100) Si, respectively. Comparisons to experimental data for MOS devices with metal and polysilicon gates, ultrathin dielectrics of SiO/sub 2/, Si/sub 3/N/sub 4/, and high-/spl kappa/ (e.g., HfO/sub 2/) gate stacks on (100) Si with EOTs down to /spl sim/ 1-nm show excellent agreement.     

A wide-band and low-driving-power phase modulator employing a Ti:LiNbO/sub 3/ optical waveguide at 1.5 mu m

A wide-band and low-driving-power Ti:LiNbO/sub 3/ optical modulator at 1.5- mu m wavelength is described. A relatively thick SiO/sub 2/ buffer layer is effectively utilized to improve phase velocity mismatch between the microwaves and optical waves. A coplanar waveguide is used as an efficient traveling-wave electrode, and is designed utilizing the upper bound calculation in the spectral domain. Wide-band modulation of 12 GHz (3 dB optical and 6 dB electrical cutoff frequency) and small driving-power-to-modulation-bandwidth ratio of 20 mW/GHz are realized.<>     

Highly efficient 40 GHz waveguide InGaAs p-i-n photodiode employing multimode waveguide structure

The authors describe the design procedure of a highly efficient waveguide p-i-n photodiode. The efficiency of the waveguide InP/InGaAsP ( lambda /sub g/=1.3 mu m)/InGaAs/InGaAsP ( lambda /sub g/=1.3 mu m)/InP p-i-n photodiode is calculated using the step-segment method and overlap-integral between the optical field of a fiber and that of the photodiode. A remarkably high coupling efficiency to a fiber can be obtained by using a multimode waveguide structure. The fabricated device has an external quantum efficiency of 68% as well as 3 dB bandwidth of higher than 40 GHz at a 1.55 mu m wavelength.<>     

Second-harmonic generation in ion-implanted KTiOPO/sub 4/ planar waveguides

The first example of second harmonic generation (SHG) in an ion implanted KTiOPO/sub 4/ waveguide is reported. This was formed by helium implantation, and SHG was achieved using zero order mode phase matching at lambda approximately=1.07 mu m. The results indicate that the high nonlinearity remains in the guiding region after implantation. The conversion efficiency in the guide is estimated to be >10% for approximately 1 mu J 20 ns pulsed excitation.<>     

Optimized breakdown probabilities in Al/sub 0.6/Ga/sub 0.4/As-GaAs heterojunction avalanche photodiodes

Recently, it has been shown that the noise characteristics of heterojunction Al/sub 0.6/Ga/sub 0.4/As-GaAs avalanche photodiodes (APDs) can be optimized by proper selection of the width of the Al/sub 0.6/Ga/sub 0.4/As layer. Similar trends have also been shown theoretically for the bandwidth characteristics. The resulting noise reduction and potential bandwidth enhancement have been attributed to the fact that the high bandgap Al/sub 0.6/Ga/sub 0.4/As layer serves to energize the injected electrons, thereby minimizing their first dead space in the GaAs layer. We show theoretically that the same optimized structures yield optimal breakdown-probability characteristics when the APD is operated in Geiger mode. The steep breakdown-probability characteristics, as a function of the excess bias, of thick multiplication regions (e.g., in a 1000-nm GaAs homojunction) can be mimicked in much thinner optimized Al/sub 0.6/Ga/sub 0.4/As-GaAs APDs (e.g., in a 40-nm Al/sub 0.6/Ga/sub 0.4/As and 200-nm GaAs structure) with the added advantage of having a reduced breakdown voltage (e.g., from 36.5 V to 13.7 V).     

Measurement of gain, group index, group velocity dispersion, and linewidth enhancement factor of an InGaN multiple quantum-well laser diode

Gain, group index, group velocity dispersion (GVD), temperature variation of refractive index, and linewidth enhancement factor of an In/sub 0.15/Ga/sub 0.85/N/In/sub 0.02/Ga/sub 0.98/N multiple quantum-well blue laser diode was measured using the Fourier transform method as a function of wavelength from 400 to 410 nm. At the lasing wavelength (403.5 nm), the group index is 3.4, the GVD (dn/sub g//d/spl lambda/) is -37 /spl mu/m/sup -1/, the temperature variation of refractive index dn/dT is 1.3/spl times/10/sup -4/ K/sup -1/, and the linewidth enhancement factor is 5.6.     

Application of high-quality SiO/sub 2/ grown by multipolar ECR source to Si/SiGe MISFET

A 5 nm-thick SiO/sub 2/ gate was grown on an Si (p/sup +/)/Si/sub 0.8/Ge/sub 0.2/ modulation-doped heterostructure at 26 degrees C with an oxygen plasma generated by a multipolar electron cyclotron resonance source. The ultrathin oxide has breakdown field >12 MV/cm and fixed charge density approximately 3*10/sup 16/ cm/sup -2/. Leakage current as low as 1 mu A was obtained with the gate biased at 4 V. The MISFET with 0.25*25 mu m/sup 2/ gate shows maximum drain current of 41.6 mA/mm and peak transconductance of 21 mS/mm.<>     

Photo-CVD SiO/sub 2/ layers on AlGaN and AlGaN-GaN MOSHFET

High-quality SiO/sub 2/ was successfully deposited onto AlGaN by photochemical vapor deposition (photo-CVD) using a D/sub 2/ lamp as the excitation source. The resulting interface state density was only 1.1 /spl times/ 10/sup 11/ cm/sup -2/eV/sup -1/, and the oxide leakage current was dominated by Poole-Frenkel emission. Compared with AlGaN-GaN metal-semiconductor HFET (MESHFETs) with similar structure, the gate leakage current is reduced by more than four orders of magnitude by using the photo-CVD oxide layer as gate oxide in AlGaN-GaN metal-oxide-semiconductor heterojunction field-effect transistors (MOSHFETs). With a 2-/spl mu/m gate, the saturated I/sub ds/, maximum g/sub m/ and gate voltage swing (GVS) of the fabricated nitride-based MOSHFET were 572 mA/mm, 68 mS/mm, and 8 V, respectively.     

Complementary metal-oxide-semiconductor thin-film transistor circuits from a high-temperature polycrystalline silicon process on steel foil substrates

We fabricated CMOS circuits from polycrystalline silicon films on steel foil substrates at process temperatures up to 950/spl deg/C. The substrates were 0.2-mm thick steel foil coated with 0.5-/spl mu/m thick SiO/sub 2/. We employed silicon crystallization times ranging from 6 h (600/spl deg/C) to 20 s (950/spl deg/C). Thin-film transistors (TFTs) were made in either self-aligned or nonself-aligned geometries. The gate dielectric was SiO/sub 2/ made by thermal oxidation or from deposited SiO/sub 2/. The field-effect mobilities reach 64 cm/sup 2//Vs for electrons and 22 cm/sup 2//Vs for holes. Complementary metal-oxide-silicon (CMOS) circuits were fabricated with self-aligned TFT geometries, and exhibit ring oscillator frequencies of 1 MHz. These results lay the groundwork for polycrystalline silicon circuitry on flexible substrates for large-area electronic backplanes.     

Lanthanum codoped erbium fibre amplifier

A lanthanum codoped erbium fibre amplifier (La-Er/GeO/sub 2//SiO/sub 2/) has been investigated by comparing such an amplifier with Al-Er/GeO/sub 2//SiO/sub 2/ and Er/GeO/sub 2//SiO/sub 2/ EDFAs. A gain of more than 35 dB at a wavelength of 1.535 mu m was obtained for 1.48 mu m pump power of 35 mW, which was the highest gain among them. The gain spectral profile was moderately flattened at around 1.552 mu m and the gain peaks at 1.535 and 1.552 mu m shifted 0.5-1 nm towards the shorter wavelength region.<>     

Submilliamp threshold current (0.62 mA at 0 degrees C) and high output power (220 mW) 1.5 mu m tensile strained InGaAs single quantum well lasers

The strain dependence of the threshold current density of lambda =1.5 mu m wavelength tensile strained In/sub x/Ga/sub 1-x/As (0.22<*<0.53)-InGaAsP single quantum well (SQW) lasers is reported. The optimum indium mole fraction was found to be 0.32 (1.5% strain), resulting in TM polarised lasers with threshold current densities as low as 92 A/cm/sup 2/. Using this SQW, buried heterostructure lasers with 0.62 mA threshold and 220 mW CW output power were realised.<>