Sumiko Fujisaki

Low-voltage operation of ferroelectric poly(vinylidene fluoride-trifluoroethylene) copolymer capacitors and metal-ferroelectric-insulator-semiconductor diodes

Exceptionally low-voltage operation of organic ferroelectric capacitors and diodes was demonstrated. Ferroelectric polyvinylidene fluoride-trifluoroethylene [P(VDF-TrFE)] thin films were prepared by the solvent-cast method. Metal-ferroelectric-metal capacitors with 60-nm-thick P(VDF-TrFE) films exhibited well-saturated hysteresis curves whose coercive voltage (Vc) and remanent polarization (Pr) were 2.0V and 11.9μC∕cm2, respectively. The authors also fabricated metal-ferroelectric-insulator-semiconductor diodes with 100-nm-thick P(VDF-TrFE) films. Rectangular-shaped capacitance-voltage (C-V) hysteresis loops were obtained with a voltage sweep range narrower than 5V. The maximum memory window of 4.7V was achieved.

Organic Ferroelectric Diodes with Long Retention Characteristics Suitable for Non-Volatile Memory Applications

Retention performance of organic metal–ferroelectric–insulator–semiconductor (MFIS) diodes composed of random copolymer poly(vinylidene fluoride)-trifluoroethylene [P(VDF-TrFE)] was drastically improved by introducing poly(methyl methacrylate) (PMMA). Only a small amount of PMMA blended to P(VDF-TrFE) copolymer improved the insulating property of thin ferroelectric films. The MFIS diode with 1.65 wt % PMMA-blended P(VDF-TrFE) film achieved the retention time longer than 106 s until now and it showed no obvious degradation of switching charge. Precise control of PMMA composition and the crystallization condition made it possible to achieve the above mentioned performance.

Green-to-Yellow Continuous-Wave Operation of BeZnCdSe Quantum-Well Laser Diodes at Room Temperature

We have grown laser diode structures using highly strained BeZnCdSe quantum wells by molecular beam epitaxy and successfully obtained continuous-wave lasing in the green-to-yellow spectral region (543–570 nm) at room temperature. The green-to-yellow lasing color was tuned by simply varying the Cd content of the quaternary BeZnCdSe quantum well. The threshold current densities of 20-µm-wide lasers were found to be sufficiently low (less than 0.85 kA/cm2). This result demonstrates that BeZnCdSe is a promising material for use as the active layer in high-performance green-to-yellow laser diodes.

115/spl deg/C, 12.5-Gb/s direct modulation of 1.3-/spl mu/m InGaAlAs-MQW RWG DFB laser with notch-free grating structure for datacom applications

Direct modulation at 12.5 Gb/s of 1.3-/spl mu/m DFB RWG lasers with low-resistance notch-free gratings running at 115/spl deg/C is experimentally demonstrated, for the first time. Moreover, 10-Gb/s modulated transmission over 30 km at 115/spl deg/C was achieved.

545 nm Room-Temperature Continuous-Wave Operation of BeZnCdSe Quantum-Well Green Laser Diodes with Low Threshold Current Density

We report the growth of BeZnCdSe quantum-well laser diode (LD) structures with a short-period superlattice cladding layer and demonstrate continuous-wave lasing in the pure-green spectral region (545 nm) at room temperature. The threshold current density and voltage of a 5-?m-wide gain-guided laser were found to be 1.7 kA/cm2 and 10.4 V, respectively. This threshold current density is sufficiently low compared with that of InGaN/GaN green LDs.

Highly reliable and stable-lateral-mode operation of high-power 0.98-/spl mu/m InGaAs-InGaAsP lasers with an exponential-shaped flared stripe

A 0.98-/spl mu/m InGaAs-InGaAsP-GaAs strained quantum-well (QW) laser with an exponential-shaped flared stripe is proposed for high-power, highly reliable operation. The stripe width is wider at the front facet to reduce the optical density by widening the spot size. The stripe width is narrower at the rear facet for stable lateral-mode operation. The stripe width in the transient region is varied exponentially along the cavity for smooth mode transformation. We showed that this structure expands the spot size effectively without any deterioration in stable lateral-mode operation. The kink-occurrence output power is determined only by the stripe width at the rear facet, and the spot size at the front facet is a function only of the stripe width at the front facet. The maximum output power is 40-60% higher than that of ordinary straight-stripe lasers for the same kink-occurrence output power. Testing at 150 mW showed stable operation with an estimated lifetime of more than 200000 h at 25/spl deg/C.

High-Power Continuous-Wave Operation of BeZnCdSe Single-Quantum-Well Green Laser Diodes

The laser performance of BeZnCdSe single-quantum-well green laser diodes (LDs) was improved. In particular, high-power lasing over 50 mW was achieved. The high-resolution lasing spectrum indicates a peak wavelength of 536 nm. The far-field patterns (FFPs) of the 5-µm-wide mesa LDs show unimodal characteristics, and the perpendicular and horizontal beam-divergence angles for full width at half maximum are 21 and 2.2°, respectively. The wall-plug efficiency (WPE) of the 2-µm-wide mesa LDs is 3.6% at an optical output power of 50 mW. The internal loss (αi) and internal differential quantum efficiency (ηi) of the 10-µm-wide-mesa LDs were estimated to be 3.5 cm-1 and 0.22, respectively.

Excellent ferroelectricity of thin poly(vinylidene fluoride-trifluoroethylene) copolymer films and low voltage operation of capacitors and diodes

Characteristics of metal-ferroelectrics-metal (MFM) capacitors and metal-ferroelectrics-insulator-semi-conductor (MFIS) diodes with poly(vinylidene fluoride-trifiuoroethylene) [P(VDF-TrFE)] copolymer films thinner than 100 nm were investigated. The films were prepared by spin-cast process and were annealed at 140degC in air for crystallization. The ferroelectric properties are equivalent to those of oxide ferroelectrics, even under low voltage or high frequency operation.

10 Gbit/s avalanche photodiodes applicable to nonhermetic receiver modules

Highly reliable InAlAs-APDs have been developed for highly sensitive 10 Gbit/s receivers. Estimated lifetime is as long as 1,000,000 hours at 75/spl deg/C, and a stable operation in a dump-heat ambient (138/spl deg/C, 85%RH) was also demonstrated.

Excellent Ferroelectricity of Thin Poly(Vinylidene Fluoride-Trifluoroetylene) Copolymer Films and Low Voltage Operation of Capacitors and Diodes

Characteristics of MFM (metal-ferroelectrics-metal) capacitors and MFIS (metal-ferroelectrics-insulator-semiconductor) diodes with P(VDF-TrFE) copolymer films thinner than 100 nm were investigated. The films were prepared by spin cast process and were annealed at 140degC in air for crystallization. The ferroelectric properties are equivalent to those of oxide ferroelectrics even under low voltage or high frequency operation.