Masaru Ozaki

AlGaAsSb buffer/barrier on GaAs substrate for InAs channel devices with high electron mobility and practical reliability

InAs/AlGaAsSb deep quantum well was successfully formed on GaAs substrate and examined for two electron devices, Hall elements (HEs), and field-effect transistors (FETs). With a thin buffer layer of 600 nm AIGaAsSb on GaAs substrate, we observed high electron mobility more than 23000 cm2/Vs and extrinsic effective electron velocity of 2.2 x 107 cm/s for a 15 nm thick InAs channel at room temperature. AIGaAsSb lattice matched to InAs was discussed from the view points of insulating property, carrier confinement, and oxidization rate. Reliability data good enough for practical use were also obtained for HEs. We demonstrated AIGaAsSb as a promising buffer/barrier layers for InAs channel devices on GaAs substrate, and we discussed the possible advantages of AIGaAsSb also for InGaAs FETs.

Surface Acoustic Wave Properties of Lithium Tantalate Films Grown by Pulsed Laser Deposition

Single-crystal films of lithium tantalate ( LiTaO3) have been grown on sapphire substrates (001), (110) and (012) by pulsed laser deposition. Surface acoustic wave (SAW) and optical properties of these films have been investigated. The refractive indices of a (012) LiTaO3 film are n e=2.1712 and n0=2.1651 at 632.8 nm. The SAW velocities of propagation (V s), the temperature coefficients of the center frequency (TCF) and the electro-mechanical coupling coefficients (k2) of the films have been measured, and theoretical calculations of V s and k2 have been done. Experimental V s and k2 coincide with calculated ones. Theoretical calculations show that LiTaO3 films deposited by pulsed laser deposition are superior materials for high frequency SAW devices.

Two-dimensional electrical transport of pentacene thin films doped with iodine

The logarithmic electrical resistivities of pentacene (PEN) thin films doped with iodine in the direction parallel to the substrate plane fit the T−1/3 dependence well. This indicates that the lateral transport of the film was governed by two‐dimensional variable range hopping. In contrast, the logarithmic resistivities of the films perpendicular to the substrate were observed to be almost independent of temperature and to be weakly T−1/2 dependent. This shows that the tunneling mechanism is predominant in perpendicular transport. Two‐dimensional conduction of the film was confirmed by these transport properties, which was expected from the intercalated structure of PEN film doped with iodine.

Miniaturized InSb photovoltaic infrared sensor operating at room temperature

This paper reports the development of a novel InSb photovoltaic infrared sensor (InSb PVS) operating at room temperature. The InSb PVS consists of an InSb p+/p-/n+ structure grown on semi-insulating GaAs (100) substrate, with a p+ Al0.17In0.83Sb barrier layer between p+ and p- layers to reduce diffusion of photo-excited electrons. Photodiodes were fabricated by wet etching process and, using a 500K blackbody, we obtained D* of 2.8x108 cmHz1/2/W and RV of 1.9 kV/W at room temperature. S/N was improved with the serial connection of 700 photodiodes patterned on a 600x600 μm2 chip. Increasing the number (N) of connected photodiodes, S/N ratio was improved by a factor of N1/2. RV was constant for signals ranging from DC to 500Hz. From spectral response measurements a cut-off wavelength of 6.8 μm was obtained. The InSb PVS was flip-chip bonded on a pre-amplifier IC, allowing the shortest connection between the InSb PVS and the pre-amplifier, making the system immune to electromagnetic noise. The system was finally encapsulated by a Dual Flat Non-leaded (DFN) package with a window, which exposes the backside of the GaAs substrate allowing the infrared light incidence. The device external sizes are 2.2 mm x 2.7 mm x 0.7 mm and to our knowledge is the smallest uncooled sensor for the middle-infrared range reported until now.

Synthesis of Poly (Vinylene Sulphide)

Abstract Pure and high molecular poly(vinylene sulphide) was synthesized from 1, 2 - dichloroethylene and sodium sulphide anhydride using dimethyl sulfoxide as a solvent.

Structure and Electrical Properties of Thin Films of Linear Acene Compounds Doped with Iodine

Abstract Structure and electrical conductivities of thin films of acene compounds doped with iodine were studied. In particular, doping of thin films of pentacene (PEN) with iodine caused characteristic changes in structure and electrical conductivity. The doped films exhibited high lateral conductivity above 102 S/cm with high anisotropy of 108 and well-defined layered structure in which iodine molecules intercalated between molecular layers of PEN. Metallic transport appeared in the highly ordered film at temperatures below 240 K. Transport behavior, lateral and perpendicular to the plane, was explained by two-dimensional (2D) variable range hopping (VRH) and by the tunneling mechanism, respectively. These electrical properties were strongly correlated with the degree of molecular orientation in the film.

Synthesis of poly(vinylene sulphide) and its electrical properties

A novel polymer of poly(vinylene sulphide), synthesized from trans- 1,2-dichloroethylene and sodium sulphide, shows enhanced electrical conductivity on doping with iodine, and has an electronic structure consistent with that determined by Bredas et al. from theoretical calculations.