Takaaki Baba

Analysis of phase-separation region in wurtzite group III nitride quaternary material system using modified valence force field model

Abstract The group III (B, Al, Ga, In) nitride quaternary alloy systems are potentially useful for ultraviolet, blue, and green light-emitting devices, or high-temperature, high-power, and high-frequency electronic devices. There have been significant challenges to the epitaxial growth of these alloys and we have investigated the unstable mixing region in the phase field. The existence of an unstable mixing region is predicted based on a strictly regular solution model. The interaction parameter used in our model is analytically obtained by the valence force field model modified for wurtzite structures. From our calculations, among the group III nitride quaternary alloy systems, we find that InGaAlN system has the narrowest unstable mixing region, and that the BInAlN system has the widest unstable mixing region. The calculated interaction parameters which are the important to predict the unstable mixing region agree well with the best-fit line of experimental results for various alloy systems.

Theoretical analysis of unstable two-phase region and microscopic structure in wurtzite and zinc-blende InGaN using modified valence force field model

A model to predict material characteristics of the InGaN ternary system, which is useful for blue and green light emitting and laser diodes, with respect to an unstable two-phase region in the phase field and the first neighbor anion–cation bond length is developed. The unstable region is analyzed using a strictly regular solution model. The interaction parameter used in the analysis is obtained from a strain energy calculation using the valence force field (VFF) model, modified for both wurtzite and zinc-blende structures to avoid overestimation of the strain energy. The structural deviation from an ideal wurtzite structure in GaN and InN is also taken into account in our model. The critical temperatures found in our analysis for wurtzite InGaN and zinc-blende InGaN are 1967 and 1668 K, respectively. This suggests that, at typical growth temperatures around 800 °C, a wide unstable two-phase region exists in both wurtzite and zinc-blende structures. The modified VFF model can also predict the microscopic ...

FeRAM circuit technology for system on a chip

The ferroelectric memory (FeRAM) has a great advantage for system on a chip, since FeRAM not only supports non-volatility but also delivers a fast memory access similar to that of DRAM. To enhance the applicability of FeRAM for embedded reconfigurable hardware, three circuit technologies are discussed in this paper. Simulation and measurement data confirmed that both power consumption and memory area can be substantially reduced, making FeRAM the most promising new technology for implementing high-performance, low-power reconfigurable hardware.

Object recognition with luminance, rotation and location invariance

We propose a neural network based on image synthesis, histogram adaptive quantization and the discrete cosine transformation (DCT) for object recognition with luminance, rotation and location invariance. An efficient representation of the invariant features is constructed using a three-dimensional memory structure. The performance of luminance and rotation invariance is illustrated by reduced error rates in face recognition. The error rate of using a two-dimensional DCT is improved from 13.6% to 2.4% with the aid of the proposed image synthesis procedure. The 2.4% error rate is better than all previously reported results using Karhunen-Loeve (1990) transform convolution networks and eigenface models. In using the DCT, our approach also enjoys the additional advantage of greatly reduced computational complexity.

Two-dimensional analysis of self-sustained pulsation for narrow-stripe AlGaAs lasers

Self-sustained pulsation in narrow stripe geometry AlGaAs laser diodes is investigated numerically and experimentally. By taking account of the time-dependent two-dimensional optical field, carrier spreading in the cladding layers, and multilongitudinal modes, we succeeded in clarifying the mechanism for the pulsation. Fluctuation of the optical field plays an important role in forming saturable absorption. The numerical analysis clearly shows that our newly proposed real refractive index-guided structure is very suitable for a pulsation laser in which the optical field distribution and current spreading can be independently controlled. Furthermore, me show that the new structure gives much lower threshold current than that of a conventional loss-guided structure. These predicted advantages of the real refractive index-guided structure are verified experimentally with good agreement. >

Analysis of Unstable Two-Phase Region in Wurtzite Group III Nitride Ternary Alloy Using Modified Valence Force Field Model

The Group III-nitride ternary system is studied with respect to an unstable two-phase region in the phase field. The unstable two-phase region is analyzed using a strictly regular solution model. The interaction parameter used in the analysis is obtained from a strain energy calculation using the valence force field model, modified for both wurtzite and zinc-blende structures to avoid overestimation of the strain energy. The structural deviation from an ideal wurtzite structure in InN, GaN, and AlN is also taken into account in our model. According to the calculated results of the interaction parameters, the critical temperature for wurtzite InGaN, InAlN, and GaAlN are found to be 1967 K, 3399 K, and 181 K, respectively. This suggests that, at a typical growth temperature of 800–1000°C a wide unstable two-phase region exists in both InGaN and InAlN. In order to show the validity of our calculation results, we compare the calculated results and the experimental results using the calculation of the interaction parameter for the InGaAs system. The calculated results agree well with the experimental results.

A DCT-based adaptive metric learning model using asymptotic local information measure

We present an adaptive metric learning vector quantization procedure based on the discrete-cosine transform (DCT) for accurate face recognition used in multimedia applications. Since the set of learning samples may be small, we employ a mixture model of prior distributions. The model selection method, which minimizes the cross entropy between the real distribution and the modeled one, is presented to optimize the mixture number and local metric parameters. The structural risk minimization is used to facilitate an asymptotic approximation of the cross entropy for models of fixed complexity. We also provide a formula to estimate the model complexity derived from the minimum description length criterion. The structural risk minimization method proposed achieves an recognition error rate of 2.29% using the ORL database, which is better than previously reported numbers using the Karhunen-Loeve transform convolution network, the hidden Markov model and the eigenface model.

Observation of Thermally Generated Carrier in Charge Coupled Devices

The build-up of thermally-generated carriers in a charge coupled device (CCD) is investigated by considering a generation model proposed by Zerbst that characterizes the transient response of an MOS capacitor. By applying clock pulses in a holding mode to a pair of electrodes of a 4-phase, 128-bit CCD shift register, noise signals of the generated carriers were observed when the duration of the holding mode reached several msec. By comparing experimental results with the theoretical transient response derived from the Zerbst model, the minority carrier lifetime τ and the surface generation velocity SG are determined to be in reasonable agreement with the values evaluated from transient responses of the MOS capacitor.

A Basic Approach to a Digital Color Camera System

A basic approach to the realization of a digital color camera system is presented. The purpose of this development is to shift the primary signal processing function from an analog domain to a digital domain, thereby increasing the level of possible IC integration.

Multi-longitudinal-mode two-dimensional analysis of self-sustained pulsating laser diodes

Summary form only given. The structural dependence of self-sustained pulsation in AlGaAs laser diodes is quantitively analyzed for the first time, with the incorporation of the two-dimensional distribution of carriers and photons into the multi-longitudinal-mode rate equations.