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High permittivity (high-k) gate dielectrics were fabricated using the plasma oxidation of Hf metal/SiO2/Si followed by the post-deposition annealing (PDA), which induced a solid-phase reaction between HfOx and SiO2. The oxidation time and PDA temperature affected the equivalent oxide thickness (EOT) and the leakage current density of the high-k dielectric films. The interfacial structure of the high-k dielectric film/Si was transformed from HfOx/SiO2/Si to HfSixOy/Si after the PDA, which led to a reduction in EOT to 1.15 nm due to a decrease in the thickness of SiO2. These high-k dielectric film structures were investigated by X-ray photoelectron spectroscopy. The leakage current density of high-k dielectric film was approximately four orders of magnitude lower than that of SiO2.

Self-sustained-pulsing A1GaInP laser diodes having very low intensity noise characteristics were successfully demonstrated by adopting a novel structure, which has highly doped saturable absorbing layer. Short carrier lifetime, which is indispensable for self-sustained pulsation, was realized by applying highly doped saturable absorbing layer. Self-pulsing laser diodes with the lasing wavelength of 650nm-band were fabricated, resulting in the threshold current of 76mA at 20°C. The relative intensity noise (RIN) was below - 138dB/Hz in the temperature range 20-60°C at the average output power of 5mW.

We have developed 680-nm-band AlGalnP visible laser diodes having very lowintensity noise with stable self-sustained pulsation. The pulsation characteristics were affected by current spreading outside the ridge stripe. We obtained AlGalnP visible laser diodes with stable self-sustained pulsation by optimizing the ridge structure. The lasers achieved relative intensity noise (RIN) as low as-136 dB Hz−1 in the temperature range 20–50°C at 3 mW.

Self‐sustained pulsating 650‐nm‐band AlGaInP visible lasers were fabricated by adopting a new structure, which has a highly doped saturable absorbing (HDSA) layer. Since the doping level and the thickness of the HDSA layer could be controlled accurately by using metalorganic vapor phase epitaxy growth technique, a stable operation of self‐sustained pulsation up to 60 °C was obtained. The lasers operated over 1350 h under the average output power of 5 mW at 60 °C. The relative intensity noise values were below −136 dB/Hz in the temperature ranging from 20–60 °C and remained unchanged after life test.

High-power 650-nm-band AlGaInP visible laser diodes having stable fundamental-transverse-mode at high temperatures were produced using electron cyclotron resonance reactive ion beam etching (ECR-RIBE). Epilayers were etched using a Cl2/N2mixture gas, resulting in very smooth surfaces and symmetric laser mesas. Lasers that are 700-µm-long and 6%/80% coated were fabricated. The typical threshold current of these devices was as low as 46 mA at room temperature, and a stable fundamental-mode operation over 30 mW is obtained up to 70°C. The lasers operated for over 1000 h at 60°C under an output power of 25 mW, and their degradation rate was as low as lasers fabricated by the ordinary wet etching process.

650 nm-band self-pulsing lasers which exhibit an extremely low laser beam profile aspect ratio (2.6) and a small astigmatism (2 µm) were successfully demonstrated by optimizing the design of the layer structure. Low-noise self-pulsing lasers have been developed as a light source for optical disc systems. In the case of mounting the lasers on optical systems, a low aspect ratio and a small astigmatism are required in order to realize high optical coupling efficiency and good optical focusing characteristics. In this paper, we report a reduction of the aspect ratio while maintaining a small astigmatism in self-pulsing AlGaInP lasers with a saturable absorbing (SA) layer by optimizing the optical confinement and compressive strain in the SA layer. Simultaneously, a very low intensity noise characteristic up to 50° C was confirmed by stable self-sustained pulsation characteristics.

A novel structure of a vertical-cavity surface-emitting laser (VCSEL) was proposed and demonstrated. Using a common-anode configuration, lower mesa height and lower electrical resistance were realized. The threshold current was 6 mA for a 10-µm-diameter device under room-temperature pulsed operation. The lasing wavelength was 939 nm. This configuration is suitable for large-scale integration. We also propose an optoelectronic integrated circuit (OEIC) with the common-anode configuration, which consists of a VCSEL and a heterostructure phototransistor (HPT) for optical parallel processing.

In case of employing a wedge nozzle for CO2 Gasdynamic Laser (GDL), it is necessary to consider generating an oblique shock wave at the nozzle exit. The translational temperature of the gas increases behind the oblique shock wave. Therefore, the population inversion becomes extinct and the small signal gain is decreased. The laser medium is reheated by passing through the oblique shock wave. In this paper, two dimensional numelical analysis which considers the influence of the oblique shock wave was carried out. In the shock wave configuration, good agreement between the schlieren photograph and the result of calculation is obtained. Experimental value of small signal gain coefficient agrees well with the calculated one.