Low-field mobilities and velocity versus electric field relations are among the key input parameters for drift-diffusion simulations of field-effect and bipolar transistors. For example, most device simulations that treat scattering from ionized impurities contain mobilities or velocity versus field relations based on the Born approximation (BA). The BA is insensitive to the sign of the charged impurity and is especially poor for ionized impurity scattering because of the relatively strong scattering of long-wavelength carriers, which have low energies, and therefore violate the validity condition for the BA. Such carriers occur at high symmetry points in the Brillouin zone and are critical for device behavior. There has been a tendency in the past to assume that majority and minority mobilities are equal. This assumption can lead to incorrect interpretations of device data and thereby misleading design strategies based on such simulations. We have calculated the majority electron and minority hole mobilities in GaAs at 300 K for donor densities between 51016 and 11019 cm-3 and the majority hole and minority electron mobilities for acceptor densities between 51016 and 11020 cm-3. We have included all the important scattering mechanisms for GaAs: acoustic phonon, polar optic phonon, nonpolar optic phonon (holes only), piezoelectric, ionized impurity, carrier-carrier, and plasmon scattering. The ionized impurity and carrier-carrier scattering processes have been calculated with a quantum mechanical phase-shift analysis to obtain more accurate matrix elements for these two scattering mechanisms. We compare the total scattering rate for majority electrons due to ionized impurities based on exact phase shifts and on the BA used by Brooks-Herring. We also present additional data that show the differences between the exact phase-shift analyses and the BA for majority electron scattering rates as functions of carrier energy and scattering angle. These results show that the calculated low-field mobilities are in good agreement with experiment, but they predict that at high dopant densities minority mobilities should increase with increasing dopant density for a short range of densities. This effect occurs because of the reduction of plasmon scattering and the removal of carriers from carrier-carrier scattering because of the Pauli exclusion principle. Some recent experiments support this finding. These results are important for device modeling because of the need to have reliable values for the minority mobilities and velocity-field relations.

Several issues on semiconductor lasers with low dimensional quantum systems are discussed. First, described are fabrication techniques for quantum wire and box structures, particularly a selective growth MOCVD growth technique which have been recently developed. Using this technique, we obtained 20 nm15 nm triangular-shaped quantum wire structures. Next, we investigate band structures of the quantum wires having strain effects, including lasing characteristics of quantum wire lasers with the strain effects. Finally we discuss importance to control both the electron wave mode and the optical wave mode for future high performance lasers, which leads to the concept of quantum micro-lasers. In order to demonstrate possibility to control the spontaneous mode in the laser cavity, an experimental result is shown on enhancement and inhibition effects of the spontaneous emission mode in a vertical cavity laser having two kinds of the quantum well.

Several issues on semiconductor lasers with low dimensional quantum systems are discussed. First, described are fabrication techniques for quantum wire and box structures, particularly a selective growth MOCVD growth technique which have been recently developed. Using this technique, we obtained 20 nm 15 nm triangular-shaped quantum wire structures. Next, we investigate band structures of the quantum wires having strain effects, including lasing characteristics of quantum wire lasers with the strain effects. Finally we discuss importance to control both the electron wave mode and the optical wave mode for future high performance lasers, which leads to the concept of quantum micro-lasers. In order to demonstrate possibility to control the spontaneous mode in the laser cavity, an experimental result is shown on enhancement and inhibition effects of the spontaneous emission mode in a vertical cavity laser having two kinds of the quantum well.

In this paper, we present a new image compression scheme, Projection-VQ, based on reconstruction from vector quantized projections. We can easily deal with the blocks of larger size in Projection-VQ than in conventional VQ schemes, because the dimension of vectors in projection domain is, in general, much smaller than that in the spatial domain. In Projection-VQ, the image can be reconstructed without destroying edge sharpness in the process since the projection data having the edge information are preferentially transmitted. There are several good algorithms of reconstructing an image from projections. However, we use a new modified reconstruction algorithm suitable for a variable bit rate image coding system. We allocate the bits depending on the characteristics of the block images. Our simulation results show that the performances are superior to the ordinary VQ schemes in PSNR, and that the improvement in subjective image quality is substantial.

The heterointerfaces of Al0.3Ga0.7As/GaAs single quantum wells (SQWs) and the characteristics of SQW lasers grown on Si substrates with Al0.5Ga0.5As/Al0.55Ga0.45P intermediate layers (AlGaAs/AlGaP ILs) entirely by metalorganic chemical vapor deposition (MOCVD) are reported. The effects of thermal cycle annealing on the crystallinity and the lasing characteristics of GaAs/Si are also reported. By using the AlGaAs/AlGaP ILs, SQWs with a specular surface morphology and a smoother heterointerface can be grown on a Si substrate. Thermal cycle annealing is found to improve the crystallinity of GaAs/Si and to contribute to room-temperature continuous-wave operation of lasers on Si substrates. The combinations of the techniques of AlGaAs/AlGaP ILs and thermal cycle annealing improve the lasing characteristics: an average threshold current density of 1.83 kA/cm2, an average differential quantum efficiency of 52%, an internal quantum efficiency of 83%, an intrinsic mode loss coefficient of 23cm-1, a differential gain coefficient of 1.9cm/A, and a transparency current density of 266 A/cm2, which are superior to those of the two-step-grown laser on a Si substrate. The improvements of the lasing characteristics result from the smooth heterointerfaces of the AlGaAs/AlGaP ILs.

Transmittance distribution along a horizontal line in LCDs addressed by amorphous silicon TFTs was investigated using measurements and calculations. Nonuniformity of the distribution, in which the transmittance increased with increasing distance from the left edge of the LCD, was observed in a 10 inch diagonal TFT-LCD. The cause of the nonuniformity was attributed to the decrease in voltage drop due to the gate source parasitic capacitance and the increase in gate voltage fall time due to large line resistance, based on the measurements of voltage drops in TFT test elements and calculations considering the decrease in voltage drop. The distribution could be improved by reducing the line resistance and parasitic capacitance in the actual LCD.

The heterointerfaces of Al0.3Ga0.7As/GaAs single quantum wells (SQWs) and the characteristics of SQW lasers grown on Si substrates with Al0.5Ga0.5As/Al0.55Ga0.45P intermediate layers (AlGaAs/AlGaP ILs) entirely by metalorganic chemical vapor deposition (MOCVD) are reported. The effects of thermal cycle annealing on the crystallinity and the lasing characteristics of GaAs/Si are also reported. By using the AlGaAs/AlGaP ILs, SQWs with a specular surface morphology and a smoother heterointerface can be grown on a Si substrate. Thermal cycle annealing is found to improve the crystallinity of GaAs/Si and to contribute to room-temperature continuous-wave operation of lasers on Si substrates. The combinations of the techniques of AlGaAs/AlGaP ILs and thermal cycle annealing improve the lasing characteristics: an average threshold current density of 1.83 kA/cm2, an average differential quantum efficiency of 52%, an internal quantum efficiency of 83%, an intrinsic mode loss coefficient of 23 cm-1, a differential gain coefficient of 1.9 cm/A, and a transparency current density of 266 A/cm2, which are superior to those of the two-step-grown laser on a Si substrate. The improvements of the lasing characteristics result from the smooth heterointerfaces of the AlGaAs/AlGaP ILs.

We consider applications of optical solitons to signal processing. Soliton switching devices promise ultrafast operation and compatibility with communications systems using optical pulses. Quantum soliton effects include broadband squeezing and quantum nondemolition measurements, and can reduce noise and increase sensitivities of optical measurements. We report the demonstration of two-color soliton switching and describe progress towards implementation of quantum nondemolition measurement of photon number using soliton collisions.

We consider applications of optical solitons to signal processing. Soliton switching devices promise ultrafast operation and compatibility with communications systems using optical pulses. Quantum soliton effects include broadband squeezing and quantum nondemolition measurements, and can reduce noise and increase sensitivities of optical measurements. We report the demonstration of two-color soliton switching and describe progress towards implementation of quantum nondemolition measurement of photon number using soliton collisions.