Susumu Fukuda

Second Harmonic Generation in As-Sputtered ZnO Optical Waveguide

SHG in an as-sputtered ZnO optical waveguide on a fused-quartz substrate has been performed with a Nd: YAG laser at 1.064 µm wavelength. For 150 mW fundamental input power, the observed conversion efficiency is about 4.9×10-6. The phase-matched interaction length of 2.5 mm is about 125 times larger than the previous result. The results reveal another potential use of sputtered ZnO film in integrated optical applications.

Acousto‐optic properties of tellurium at 10.6 μm

Experimental results are described for the acousto‐optic properties of Te at the 10.6‐μm wavelength of CO2 laser light. It is found that Te possesses exceptionally large figures of merit. The largest value of M, 5850×10−18 sec3/g, is obtained for a longitudinal acoustic wave propagating in the x direction and incident light polarized along the z axis. Five of the eight independent photoelastic tensor components are calculated from the measured figures of merit and the effects of optical activity on these results are discussed. The practical applicability of Te as an acousto‐optic medium is evaluated.

Acoustic and Acousto-Optic Properties of Amorphous Se

The acoustic and acousto-optic properties of amorphous Se have been studied. It was found that amorphous Se possesses large acousto-optic figures or merit almost comparable to those of single-crystal Te. The values obtained are M11=981×10-18 s3/g and M12=1080×10-18 s3/g at 10.6 µm. The two non-vanishing independent photoelastic tensor components were determined as p11=0.357 and p12=0.375 at 10.6 µm. In spite of these large figures of merit, pure amorphous Se is not very satisfactory as an acousto-optic medium, since the glass transition temperature of about 30°C makes the material both optically and elastically very unstable at room temperature. However, it was found that the addition of several percent of arsenic raises the glass transition temperature significantly and improves the acoustic and acousto-optic properties.

Acoustooptic Interactions in Piezoelectric Semiconductor: Tellurium

This paper reviews acoustooptic properties of Te at the infrared wavelength of 10.6~~~. It has been found that Te possesses exceptionally large figures of merit. the practical applicability is evaluated in comparison with other important infrared acoustooptic materials. semiconductor, it is theoretically expected that acoustooptic diffraction in Te should be considerably influenced by simultaneous presence of piezoelectricity and conductivity through the piezoelectric coupling. prediction, an appreciable diffraction has been observed in Te in an intrinsic region, which can be attributed to the p eriodic modulation of the dielectric constant due to acoustoelectrica lly induced free-carrier d ensity waves. Outline of these interactions is also described. Based on the experimental results,

Doped Channel HFET with Effective Lateral Energy Modulation for High Power Enhancement Operation

l.Introduction Doped channel heterostructure FET (DC-HFET) can match many figures of merit of the more established HEMT. Due to the undoped wide band gap barriers [1.], DC-HFET can avoid several inherent drawbacks of HEMT. By using the doped channel scheme, instead of the modulation doped one, DC-HFET could attain a better carrier confinement of high carrier density without any real space transfer even under the enhancement mode operation. The DC-HFET reported to date in fact has shown superior characteristics [2] t3l t4l. Nevertheless, an undoped banier layer commonly buried under the gate electrode inevitably causes large channel series resistance. This series resistance degrades DC characteristics such as transconductance [5], drain conductance and knee voltage, resulting in poor output power characteristics. We have already proposed the laterally modulated energy band structure that can reduce the parasitic resistance. The excellent RF characteristics such as fT of 1L0GHz and fmax of 200GHz were obtained by our 0.2um gate DCHFET [6]. The reduction of parasitic resistance can improve the power characteristics as well as the small signal properties. In this paper we demonstrate the effect of our doped channel scheme for power devices. The fabricated devices show excellent RF and DC characteristics superior to that of conventional enhancement HFET.

Current Saturation Related to Internal Potential Barrier in Se Crystal

Current saturation is observed at electric fields higher than 10 kV/cm in Se crystal under illumination at 77–290 K. The transient time from the initial current value to the final current value is 1–10 ms for a single pulse measurement, and 25 µs for repeated pulses at 1 kHz for example. The saturation is not caused by the acoustoelectric effect but by the field quenching effect of photoconductivity explained by the barrier model and the dislocation recombination model. It is concluded that the potential barrier height increases by the application of a high electric field large enough so as to overcome the decrease by illumination, and the final value of the current saturates at high electric fields. The relation between the applied high electric field and the rate of photoconductivity decay is also measured, and the results are explained in terms of the equations developed from the models.