Monolithic integration of InGaAsP/InP lasers and heterostructure bipolar transistors by selective area epitaxy

The authors describe the use of selective area epitaxy to prepare monolithically integrated lasers and heterostructure bipolar transistors based on InGaAsP/InP. Selective growth offers a versatile method of lateral integration of structurally dissimilar devices with the different device structures grown side by side in different growth cycles. Individual devices can be optimised separately without any performance compromise. Bipolar transistors grown on the semi-insulating current blocking layers of the buried heterostructure lasers show high gain, high breakdown voltage and excellent high current stability. Laser threshold is reached at a base current as low as 160 mu A and the light output is linear with current to 10 mW.<>     

Special Important Aspects of the Thomson Effect

A comprehensive study of the mechanisms of heating and cooling originating from an electrical current in semiconductor devices is reported. The variation in temperature associated with the Peltier effect is not related to the presence of heat sources and sinks if the heat flux is correctly determined. The Thomson effect is commonly regarded as a heat source/sink proportional to the Thomson coefficient, which is added to the Joule heating. In the present work, we will show that this formulation of the Thomson effect is not sufficiently clear. When the heat flux is correctly defined, the Thomson heat source/sink is proportional to the Seebeck coefficient. In the conditions in which the Peltier effect takes place, the temperature gradient is created, and, consequently, the Thomson effect will occur naturally.     

Thermoelectric Properties of NaCo<Subscript>2–<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>

NaCo₂O₄ has one of the highest figures of merit among all ceramic thermoelectric materials. Because of its large thermopower and low resistivity, the ceramic oxide NaCo₂O₄ is a promising candidate for potential thermoelectric applications. NaCo₂O₄ is, moreover, a ceramic compound with high decomposition temperature and chemical stability in air and it does not contain any toxic elements. Like all 3-d transition ions, Co ions have multiple spin and oxidation states. In this investigation, thermopower and electrical conductivity of NaCo₂O₄ as a function of substitution of Co by Fe ions were measured. Fe substitution for Co causes resistivity to increase, whereas the Seebeck coefficient remained nearly invariant, especially above 330 K. An erratum to this article can be found at     

Measurement of RF Transmission Mode in ITER Relevant EC H&;CD Transmission Line

The preliminary results of mode measurement in the ITER relevant 40 m long transmission test line composed from 63.5 mm diameter corrugated waveguides and miter bends are presented. The field patterns were measured by taking temperature profiles on a paper screen placed in front of the waveguide end using an infrared imaging camera. The complex electric field at the waveguide end was retrieved from the measured temperature profiles. As a result, the transmission power includes 87% of HE₁₁ mode and 6% of LP₁₁ odd (HE₂₁+TE₀₁) mode and small ratios of other modes. The mode content had small dependence on length of the transmission line. This result indicated that the higher order mode content generated at the input of the transmission line is conserved and propagated through the transmission line. This suggests that the initial RF coupling to the waveguide is critical since it affects the launcher efficiency.     

A high-voltage modulator for high-power RF source research

The design, construction, and operating results of a high-voltage modulator system capable of generating 700-kV, 2.5-μs pulses at 5 p.p.s. into a load of 900 Ω are presented. The modular is used to energize a variety of high power microwave devices requiring voltage stability and reproducibility. Voltage ripple is less than 0.2% during the 1.0-μs flat top, with a shot-to-shot voltage variation of less than 0.1%. The primary circuit consists of two seven-stage tunable Rayleigh-type pulse-forming networks (PFNs) connected in parallel with a total impedance of 2.25 Ω, a total capacitance of 0.56 μF, and a total inductance of 2.8 μH. The PFN is charged by a highly stable 80-kV capacitor charging power supply (0.1% RMS voltage ripple) at a rate of 10 KJ/s. The total energy stored (1.5 kJ) is released through an ITT F-187 thyratron into a 20:1 pulse transformer, which generates 700-kV, 2.5-μs pulses. By changing the transformer, it was possible to obtain 250-kV, 1.70-kA pulses for driving low-impedance relativistic magnetron diodes. The flat-top voltage generated by the modulator is highly desirable for driving RF sources requiring high-quality electron beams, such as free-electron lasers (FELs) and cyclotron autoresonance masers (CARMs). The modulator performance in the relativistic magnetron and CARM experiments is described     

High temperature operation of lattice matched and strained InGaAs-InP quantum well lasers

The temperature dependence of lattice matched and strained InGaAs-InP quantum well lasers operating between 1.48 and 1.56 mu m is described. Devices grown under tensile and compressive strain, with an In concentration in the range of 0.43>     

Modifications of the Cubic Phase Function

By introducing a symmetric pair of time instants, a modification of the Cubic phase （CP） function, named as the Quartic phase （QP） function, is proposed to estimate the quadratic FM signal. The performance in terms of estimate bias and variance is presented via the first-order permutation principle. Two extensions are presented for multiple components and the cubic FM signals. Both theoretical analysis and numerical examples confirm that the QP function and its extensions provide a number of advantages, such as： （1） lower asymptotic Mean-square error （MSE） for the estimate of the third-order phase pa- rameter at high SNR; （2） a better capability of discriminating multicomponent signals; （3） a lower SNR threshold for the estimates of the cubic FM signal.     

Parametric estimation of 2D cubic phase signals using high-order Wigner distribution with genetic algorithm

Multidimensional Systems and Signal Processing - A two-dimensional (2D) high-order Wigner distribution (HO-WD) is proposed for parameter estimation of 2D polynomial phase signals (PPSs). The...