Voltage Tunability of Quantum Cascade Lasers

The voltage tunability of three types of quantum cascade laser designs is investigated. The tuning coefficients and tuning ranges of electroluminescence and laser emission from all designs are measured and compared with the calculated results. A reduced tunability was observed in all lasers above threshold. This is attributed to the decrease of resistance across the laser active region (AR) as the photon density increases. A resumed tunability high above threshold occurs in all lasers with anticrossed injector ground and upper laser states. Lasers based on the anticrossed diagonal transition are tunable above threshold, with a tuning range of about 30 ${hbox {cm}}^{-1}$ ($sim$ 3% of the laser emission wavenumber), i.e., a tuning rate of 750 ${hbox {cm}}^{-1} hbox{V}^{-1}cdot hbox{period}^{-1}$ of the AR and the injector.      

Cooperative Quantum Cutting in Yb $^{3+}$–Tb $^{3+}$ Codoped Borosilicate Glasses

Quantum cutting down-conversion (DC) with the emission of two near-infrared photons for each blue photon absorbed is realized in $hbox{Yb}^{3+}hbox{–}hbox{Tb}^{3+}$ codoped borosilicate glasses. With the excitation of $hbox{Tb}^{3+}$ ion by a 484-nm monochromatic light, emission from the $^{2} hbox{F} _{5/2}rightarrow ^{2} hbox{F} _{7/2}$ transition of $hbox{Yb}^{3+}$ ions is observed and this emission is proved to originate from the DC between $hbox{Tb}^{3+}$ ions and $hbox{Yb}^{3+}$ ions. Results shows that maximum quantum efficiency reach as high as 153%, which is comparable with that in oxyfluoride glass ceramics in this system. With the advantages of excellent transparence, easy shaping, good stability, and low cost, $hbox{Yb}^{3+}hbox{–}hbox{Tb}^{3+}$ codoped borosilicate glasses are potentially used as down-converter layer in silicon-based solar cells.      

A Planar CMOS Field-Emission Vacuum Magnetic Sensor

We have fabricated a CMOS vacuum magnetic sensor that exploits the deflection of an electron beam produced by field emission by a perpendicular magnetic field. The device is planar and fabricated by conventional lithography and etching processes. An extremely high magnetic field sensitivity of $hbox{4} times hbox{10}^{3}%/hbox{T}$ is reported.      

The Electrical and Interfacial Properties of Metal-High-$kappa$ Oxide-Semiconductor Field-Effect Transistors With $hbox{LaAlO}_{3}$ Gate Dielectric

$hbox{LaAlO}_{3}$ is a promising candidate for gate dielectric of future VLSI devices. In this letter, n-channel metal–oxide–semiconductor field-effect transistors with $hbox{LaAlO}_{3}$ gate dielectric were fabricated, and the electron mobility degradation mechanisms were studied. The leakage current density is $hbox{7.6} times hbox{10}^{-5} hbox{A/cm}^{2}$ at $-!$ 1 V. The dielectric constant is 17.5. The surface-recombination velocity, the minority-carrier lifetime, and the effective capture cross section of surface states were extracted from gated-diode measurement. The rate of threshold voltage change with temperature $(Delta V_{T} / Delta T)$ from 11 K to 400 K is $-!$ 1.51 mV/K, and the electron mobility limited by surface roughness is proportional to $E_{rm eff}^{-0.66}$.      

Effect of Oxygen Pressure on the Electrical Properties of $hbox{Bi}_{5} hbox{Nb}_{3}hbox{O}_{15}$ Films Grown by RF Magnetron Sputtering

$hbox{Bi}_{5}hbox{Nb}_{3}hbox{O}_{15} (hbox{B}_{5}hbox{N}_{3})$ films grown under a low oxygen partial pressure (OP) of 1.7 mtorr showed a high leakage current density of 0.1 $hbox{A/cm}^{2}$ at 1.0 MV/cm. However, the leakage current density decreased with increasing OP to a minimum of $hbox{5.8} times hbox{10}^{-9} hbox{A/cm}^{2}$ for the film grown under 5.1 mtorr due to the decreased number of oxygen vacancies. This film also showed an improved breakdown field of 2.2 MV/cm and a large capacitance density of 24.9 $hbox{fF}/muhbox{m}^{2}$. The electrical properties of the film, however, deteriorated with a further increase in OP, which is probably due to the formation of oxygen interstitial ions. Therefore, superior electrical properties for the $ hbox{B}_{5}hbox{N}_{3}$ film can be obtained by careful control of OP.      

Flexible Full-Color AMOLED on Ultrathin Metal Foil

Full-color active-matrix organic light-emitting diode panels, driven by poly-Si thin-film transistors (poly-Si TFTs), were successfully fabricated on thin metal foil substrates. The p-channel poly-Si TFTs on metal foil showed a field-effect mobility of 82.9 $hbox{cm}^{2}/hbox{V}cdothbox{s}$ , subthreshold slope of 0.34 V/dec, threshold voltage of $-$ 1.67 V, and off-current of $ hbox{6.6} times hbox{10}^{-14} hbox{A}/muhbox{m}$. The 5.6-in panel had 160 $times$ RGB $times$ 350 pixels, each of which had a pixel circuit of two TFTs and one capacitor.      

Effect of Growth Temperature on InP QD Lasers

We describe the effect of growth temperature on the optical absorption, gain, and threshold current density of 730-nm emitting, metal–organic vapor phase epitaxy (MOVPE) grown, InP–AlGaInP quantum-dot lasers. Decreasing the growth temperature from 750 $^{circ}hbox{C}$ to 690 $^{circ}hbox{C}$ leads to an increase in ground state absorption, while sufficient optical gain and low 300 K threshold current density is obtained in the growth temperature window between 710 $^{circ}hbox{C}$ and 730 $^{circ}hbox{C}$ . Wider (16 nm compared to 8 nm) interlayer barriers lead to lower threshold current density with 300 K values as low as 165 $hbox{Acm}^{-2}$ for 2-mm-long lasers with uncoated facets.      

The performance of optical phase-locked loops in the presence of nonnegligible loop propagation delay

The optical phase-locked loop is analyzed taking into account shot noise, phase noise, and loop propagation delay. The degradation of loop phase error due to propagation delay is evaluated in terms of the delay bandwidth productomega_{n} cdot tau_{D}. This product was found to have a maximum value of 0.736 for absolute loop stability. The resulting effect on a Costas loop system optimized for zero time delay is discussed. It is found that in order to maintain a 10^-9BER system performance withxi = 1/2^{0.5}, R = 0.85A/W,P_{DATA} = -59.2dBm, and a 1-MHz beat linewidth, the delay time must be kept below 1.8 ns. If the beat linewidth increases to 15 MHz this figure drops to 0.12 ns.     

Properties of the PbSe diode laser

Diode laser action has been obtained at 8.5μ with PbSe. This laser is of potential interest for terrestrial communications since its emission is in the 8-to-14-μ atmospheric window, a spectral region of high atmospheric transparency where attenuation due to scattering by haze is low. Fabrication techniques are described which are based on controlling carrier type and concentration by adjusting the Pb:Se ratio. Below threshold for laser action, the emission exhibits two spectral peaks, one near 8.5μ which increases superlinearly with current and another near 10.1μ which increases slowly with current. Laser action associated with the 8.5μ peak is observed above a threshold Current density of 2000 A cm^-2. From measurements which did not resolve the cavity mode structure, the emission peak was found to shift to higher energies in a [100] oriented magnetic field at the rate of7.1 times 10^{-8}eV per gauss, or 17 Mc/s per gauss. This is the expected shift if the emission is associated with band-to-band transitions. The threshold current decreased to a fraction of its zero field value in a magnetic field of approximately 10 kilogauss, then increased slowly with higher fields.     

Theoretical Modeling of a $sim {2}~mu{rm m}~{rm Tm}^{3+}$-Doped Tellurite Fiber Laser: The Influence of Cross Relaxation

A rate equation approach is used to model an experimentally realized $sim {2}~mu{rm m}~{rm Tm}^{3+}$ -doped tellurite fiber laser utilizing an in-band pumping scheme $({}^{3}H_{6}ura{}{} ^{3}F_{4})$ . Excellent agreement between the theoretically predicted and experimentally measured slope efficiency is obtained. It is shown that in order to achieve agreement between the predicted and measured thresholds it is important to include cross-relaxation mechanisms with the ${}^{3}H_{4}$ level, even with the in-band pumping scheme. By fitting the results of the model with level lifetime measurements and the threshold pump powers we have extracted the cross-relaxation parameters of Tm-doped tellurite glass.      

Multiple detection of a slowly fluctuating target (Corresp.)

A "slowly" fluctuating target is assumed to keep its radar cross section constant for the duration of several(M)dwells on target. To resolve multiple range and/or Doppler ambiguities, the received signal, which is presumably coherently processed (i.e., predetection integrated or matched filtered) over each dwell, must often be tested against a threshold, {em independently} of those on other dwells. Such a procedure is referred to as {em multiple detection}. A technique for the evaluation of a tight lower bound on the multiple-detection probabilityP_{M}, under Swerling case I statistics for the cross section, is presented in term of an infinite series and worked out in detail forP_{2}andP_{3}. Estimates on the computation error due to the truncation of the series are derived. Numerical results indicate thatP_{3}comes much closer toP_{1}than top_{1}^{3}or even toP_{1}P_{2}; at an expected signal-to-noise ratio of13dB and atP_{1} = 0.51, it obtains thatP_{3} geq 0.40, whereasP_{1}P_{2} = 0.23andp_{1}^{3} = 0.17.     

Microwave ZnO Thin-Film Transistors

We have developed ZnO thin-film transistor design and fabrication techniques to demonstrate microwave frequency operation with 2-$muhbox{m}$ gate length devices produced on GaAs substrates. Using $hbox{SiO}_{2}$ gate insulator and pulsed laser deposited ZnO active layers, a drain–current on/off ratio of $hbox{10}^{12}$, a drain–current density of 400 mA/mm, a field-effect mobility of $hbox{110} hbox{cm}^{2}!/ hbox{V}!cdothbox{s}$, and a subthreshold gate voltage swing of 109 mV/dec were achieved. Devices with Ti-gate metal had current and power gain cutoff frequencies of 500 and 400 MHz, respectively.      

Analyses of mode-hopping phenomena in an AlGaAs laser

Intensity fluctuations of the longitudinal modes of a 0.8 μm AlGaAs laser were precisely measured during the occurrence of hopping between two modes. It was found from this result that mode hopping follows the stochastics of a Poisson process. The frequency of mode hopping was measured asf_{c} = [exp [-95(I/I_{th} - 1)]] times 10^{7}(Hz). whereI/I_{th}is the injection current normalized to its threshold value. Results of analog computer simulations showed that spontaneous emission worked as a triggering force for mode hopping. Results of the analysis based on the Fokker-Planck equation were compared to the experimental results, from which the root-mean-square value of the fluctuating electric field of spontaneous emission was estimated as2.3 times 10^{2)(V/m)leqlanglesim{E}_{N} leq 3.2 times 10^{2}(V/m). It is concluded that an effective reduction of mode hopping is achieved if the laser is operated at a higher bias or if the coupling constant between the two modes is increased.     

High-Frequency ZnO Thin-Film Transistors on Si Substrates

Record microwave frequency performance was achieved with nanocrystalline ZnO thin-film transistors fabricated on Si substrates. Devices with 1.2-$muhbox{m}$ gate lengths and Au-based gate metals had current and power gain cutoff frequencies of $f_{T} = hbox{2.45} hbox{GHz}$ and $f_{max} = hbox{7.45} hbox{GHz}$ , respectively. Same devices had drain–current on/off ratios of $hbox{5} times hbox{10}^{10}$, exhibited no hysteresis effects and could be operated at a current density of 348 mA/mm. The microwave performances of devices with 1.2- and 2.1- $muhbox{m}$ gate lengths and 50- and 100-$muhbox{m}$ gate widths were compared.      

Electrical Properties of $hbox{Bi}_{5}hbox{Nb}_{3} hbox{O}_{15}$ Thin Film Grown on $hbox{TiN}/hbox{SiO}_{2}/ hbox{Si}$ at Room Temperature for Metal–Insulator–Metal Capacitors

Buckling was observed in $hbox{Bi}_{5}hbox{Nb}_{3}hbox{O}_{15}$ (BiNbO) films grown on $hbox{TiN}/hbox{SiO}_{2}/hbox{Si}$ at 300 $^{circ}hbox{C}$ but not in films grown at room temperature and annealed at 350 $^{circ}hbox{C}$. The 45-nm-thick films showed a high capacitance density and a low dissipation factor of 8.81 $hbox{fF}/muhbox{m}^{2}$ and 0.97% at 100 kHz, respectively, with a low leakage current density of 3.46 $hbox{nA}/hbox{cm}^{2}$ at 2 V. The quadratic and linear voltage coefficients of capacitance of this film were 846 $hbox{ppm}/hbox{V}^{2}$ and 137 ppm/V, respectively, with a low temperature coefficient of capacitance of 226 $hbox{ppm}/^{circ}hbox{C}$ at 100 kHz. This suggests that a BiNbO film grown on a $hbox{TiN}/ hbox{SiO}_{2}/hbox{Si}$ substrate is a good candidate material for high-performance metal–insulator–metal capacitors.      

Effective Modulation of Quadratic Voltage Coefficient of Capacitance in MIM Capacitors Using $hbox{Sm}_{2}hbox{O}_{3}/hbox{SiO}_{2}$ Dielectric Stack

We report the first demonstration of metal–insulator–metal (MIM) capacitors with $hbox{Sm}_{2}hbox{O}_{3}/hbox{SiO}_{2}$ stacked dielectrics for precision analog circuit applications. By using the “canceling effect” of the positive quadratic voltage coefficient of capacitance (VCC) of $hbox{Sm}_{2}hbox{O}_{3}$ and the negative quadratic VCC of $hbox{SiO}_{2}$, MIM capacitors with capacitance density exceeding 7.3 $hbox{fF}/muhbox{m}^{2}$ , quadratic VCC of around $-hbox{50} hbox{ppm/V}^{2}$ , and leakage current density of $hbox{1} times hbox{10}^{-7} hbox{A/cm}^{2}$ at $+$3.3 V are successfully demonstrated. The obtained capacitance density and quadratic VCC satisfy the technical requirements specified in the International Technology Roadmap for Semiconductors through the year 2013 for MIM capacitors to be used in precision analog circuit applications.      

Distributed-Feedback Quantum-Cascade Lasers at 9 $mu$m Operating in Continuous Wave Up to 423 K

Single-mode lasers operating at $lambdaapprox 9 muhbox{m}$ in continuous wave up to 423 K (150 $^{circ}hbox{C}$) were achieved by the combination of strong distributed-feedback coupling, a narrow gain active region design, low intersubband, and free-carrier losses as well as a good thermal management. Tuning of 10 $hbox{cm}^{-1}$ or 0.9% of the center frequency was achieved by heating the device. The threshold current density varies from 1.1 $hbox{kA/cm}^{2}$ at 303 K to 2.4 $hbox{kA/cm}^{2}$ at 423 K. Other devices with low electrical power consumption of 1.6 and 3.8 W for an optical output power of 16 and 100 mW have been demonstrated at 263 K.      

2.7-$mu$ m GaSb-Based Diode Lasers With Quinary Waveguide

Type-I double-quantum-well (QW) GaSb-based diode lasers operating at 2.7 $mu hbox{m}$ with room-temperature continuous-wave (CW) output power of 600 mW and peak power-conversion efficiency of 10% were designed and fabricated. The devices employed 470-nm-wide AlGaInAsSb waveguide optimized for improved device differential gain. CW threshold current density about 100 $hbox{A}/hbox{cm}^{2}$ per QW and slope efficiency of 150 mW/A were demonstrated at 16 $^{circ }hbox{C}$.      

Device characteristics of (Al,Ga)As lasers with Ga(As,Sb) active layers

Device characteristics of double heterostructure lasers with Al0.4Ga0.6As confinement layers and GaAs0.99Sb0.01active layers are presented. Average emission wavelengths have been increased from 0.87 μm for undoped active layers to 0.88 μm for2 times 10^{17}cm^-3Ge doped active layers with a "wash" melt preceding the growth of the active layer and to 0.89 μ for1 times 10^{18}cm^-3Mg doped active layers grown following a "wash" melt. Threshold currents for lasers from 21 wafers are examined for several growth conditions and compared with Al0.08Ga0.92As active layer devices. Device resistance, external quantum efficiency, device degradation, and pulsed and CW threshold currents as a function of temperature are also discussed.     

Electrical Properties of Amorphous $hbox{Bi}_{5} hbox{Nb}_{3}hbox{O}_{15}$ Thin Film for RF MIM Capacitors

Amorphous $hbox{Bi}_{5}hbox{Nb}_{3}hbox{O}_{15}(hbox{B}_{5} hbox{N}_{3})$ film grown at 300 $^{circ}hbox{C}$ showed a high-$k$ value of 71 at 100 kHz, and similar $k$ value was observed at 0.5–5.0 GHz. The 80-nm-thick film exhibited a high capacitance density of 7.8 fF/$muhbox{m}^{2}$ and a low dissipation factor of 0.95% at 100 kHz with a low leakage-current density of 1.23 nA/ $hbox{cm}^{2}$ at 1 V. The quadratic and linear voltage coefficient of capacitances of the $hbox{B}_{5}hbox{N}_{3}$ film were 438 ppm/$hbox{V}^{2}$ and 456 ppm/V, respectively, with a low temperature coefficient of capacitance of 309 ppm/$^{circ}hbox{C}$ at 100 kHz. These results confirmed the potential of the amorphous $hbox{B}_{5}hbox{N}_{3}$ film as a good candidate material for a high-performance metal–insulator–metal capacitors.