Yoshifumi Tsunekawa

GaAlAs laser diodes with metalorganic chemical vapor deposition grown ZnSe layer for injection blocking and optical confinement

A transverse mode stabilized GaAlAs laser diode which includes a ZnSe layer for the waveguide has been developed. The double heterostructure of the GaAlAs laser is formed by low‐pressure metalorganic chemical vapor deposition (MOCVD), and a ZnSe layer is grown by adduct‐source MOCVD in order to block the injection current and change the real refractive index in the lateral direction. The fundamental transverse mode oscillation of more than 15 mW is obtained with a low threshold current of 28 mA and a high quantum efficiency of 76%. An output power as high as 25 mW is achieved.

BaTiO3 based relaxor ferroelectric epitaxial thin-films for high-temperature operational capacitors

The epitaxial growth of 0.6[BaTiO3]–0.4[Bi(Mg2/3Nb1/3)O3] (BT–BMN) relaxor ferroelectric thin-films on (100) Nb doped SrTiO3 substrates has been achieved and the structure is investigated for high-temperature capacitor applications. The post growth annealing decreases the oxygen vacancy and other defects in BT–BMN films, resulting in the enhancement of dielectric constant. An insertion of intermediate SrRuO3 layers as an electrode instead of Pt, sandwiching the film, is found to be more effective in enhancing the dielectric constant. A very high dielectric constant exceeding 400 was achieved from high-temperature annealed film and the film showed an excellent dielectric constant stability of below 11% in the temperature range of 80–400 °C. This will enable smaller, high-temperature tolerant, monolithically integrated thin-film capacitors on power semiconductor devices.

Selectively embedded epitaxial growth of ZnSe by low-pressure MOCVD using dimethylzinc and dimethylselenium

Abstract Selective growth of ZnSe layers embedded flatly over a ridged GaAs substrate, whose ridge-stripes are covered with SiO2 films, has been achieved by low-pressure MOCVD using dimethylzinc (DMZn) and dimethylselenium (DMSe) as source materials. When the gas pressure is less than 50 Torr and the (DMSe)/(DMZn) mole ratio is less than 6, selective area growth is realized. On the other hand, to bring about a smooth-flat surface for embedded growth requires a minimum substrate temperature of 600°C. From these results, we discuss a selective growth mechanism of ZnSe. Furthermore, a transverse mode stabilized AlGaAs/GaAs laser diode with a low threshold current of 30 mA and a high external differential quantum efficiency of 80% has been obtained by a self-aligned fabrication process using a selectively-grown ZnSe layer for injection blocking and optical confinement.

High-performance polycrystalline silicon TFTs fabricated by high-temperature process with excimer laser annealing

Polycrystalline silicon (p-Si) thin film transistors (TFTs) were fabricated using a high temperature process that included solid phase crystallization (SPC) and dry thermal oxidation with excimer laser annealing (ELA). Raman spectroscopy, X-ray diffraction and transmission electron microscopy analyses showed that the ELA process improved the quality of p-Si films markedly. The p-Si TFTs exhibited higher performance than the SPC p-Si TFTs. The field effect mobility for n-type self-aligned TFT was (formula available in paper). The longitudinal junction diffusion length of the p-Si TFTs was shorter than that of the SPC p-Si TFTs. This is favorable for fine design rules. If optimization of amorphous silicon (a-Si) deposition and SPC conditions enables the grains of p-Si films to grow larger than the channel length and the positions of the grain boundaries are controlled, this process will produce great scaling rule merits such as single-grain Si TFTs. This fabrication process is consistent with the high temperature p-Si TFT development trend towards using large substrates, low temperatures, and fine design rules. High temperature p-Si TFTs are expected to be used in LSI circuits as silicon-on-insulator (SOI) devices in the future.