The influence of CO, CO2 and H2O gases on the stability of negative-electron-affinity (NEA) GaAs photocathodes during operation is investigated in the present work. We have found that exposure both to H2O and CO2 decreases the photocurrent of the photocathode. However, exposure to CO, which is known as a harmful gas to various photocathodes, has little effect on the photocathode stability. Furthermore, the effects of these gases on the restoration of the photocurrent by additional cesium deposition are investigated. These results are discussed with regard to the Cs/O activation layer which plays an important role in NEA GaAs photocathodes.

We have fabricated III-V gain region/Si waveguide hybrid lasers with an InP-based two-storied ridge structure using a direct bonding technology. Continuous-wave operation at a temperature of 20oC with a threshold current as low as 30 mA was obtained for a hybrid laser consisting of a Fabry-Perot cavity with facets formed on the Si waveguide, and it was achieved thanks to a high optical coupling efficiency of over 80% at the interface between the III-V gain region and the Si waveguide using a two-storied ridge structure and a taper waveguide. The wavelength tunable laser which is comprised of a Si cavity with a loop mirror and double ring filters and III-V gain regions with laser and semiconductor optical amplifier (SOA) sections was demonstrated by utilizing this hybrid structure. It exhibited a wide wavelength tuning range of 48.6 nm and an optical amplification of 10 dB by SOA.

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Arsenic-implanted self-aligned Al-gate MOSFETs have been successfully fabricated by employing ultra-clean ion implantation technology. The use of ultra high vacuum ion implanter and the suppression of the high-energy-beam-induced metal sputter contamination have enabled us to form low-leakage pn junctions by fumace arurealing at a temperature as low as 450"C. The fabricated Al-gate MOSFETs have exhibited good electrical characteristics, thus demonstratiDg a large poteDtial for application to realizing ultra-high-speed integrated circuits. 1. Introducfion and drain junctions self-aligned to the aluminum gate,