Satoru Todoroki

Temperature distribution along the striped active region in high-power GaAlAs visible lasers

Catastrophic degradation related to local heating in GaAlAs visible lasers occasionally occurs under relatively low optical output power. To develop highly reliable lasers, we used laser Raman spectroscope with an argon ion laser focused at about 1 μm≂ to evaluate the local operating temperature rise not only at the facet surface, but also along the striped active region. The local operating temperature rise in the vicinity of the facet’s active region increased exponentially up to 200 °C when the optical output power was 30 mW/facet. This high temperature causes the rapid formation of a dark region and final catastrophic degradation. The calculated temperature rise along the striped active region is about one‐half of that of the facet. The internal operating temperature is far higher than the average temperature measured by the thermal resistance method, which is considered to be a large influence on the lifetime and activation energy of lasers in practical applications.

Influence of local heating on current‐optical output power characteristics in Ga1−xAlxAs lasers

Available optical output powers from the Ga1−xAlxAs lasers are limited by the catastrophic optical damage or output power saturation due to local heating on the facet. Especially, the saturation of current‐optical output power characteristically occurs during the operations at relatively low output power. This report describes the degradation process in an active region for lasers with the striped window as an electrode with respect to current‐optical output power characteristics, electroluminescence image observation, and measurement of temperature rise at the facet and the cavity inside using laser Raman spectroscopy. The nonluminescing dark region observed in rapidly degraded lasers develops from the facet to the cavity inside. The dark region is so nonradiative that electron‐hole recombination in that region produces heat rather than light. The measured local temperature on the facet drastically rises and the area influenced by local heating extends into the cavity inside. Although the threshold curre...

Tetrahedral Amorphous Carbon Films By Filtered Cathodic Vacuum-Arc Deposition For Air-Bearing-Surface Overcoat

Measures were taken to reduce the generation of particles during the fabrication of tetrahedral amorphous carbon (ta-C) film by the double-bend filtered cathodic vacuum-arc (FCVA) method. Specifically, the use of physical and electrical filters in the plasma path reduced the number of micron-order particles that arrive at the substrate to about 1/100 the usual value. In addition, an experiment was performed to evaluate the density of pinholes of both the ta-C film fabricated by FCVA method with these filters and a hydrogenerated amorphous carbon (a-C:H) film fabricated by chemical vapor deposition (CVD) method. The results of this experiment revealed that the density of pinholes generated for a film thickness of about 3 nm was 2×103/cm2 for the ta-C film compared to 8×103/cm2 for the a-C:H film, indicating that ta-C film is much denser than a-C:H film. Furthermore, an environmental test under high-temperature and high-humidity conditions showed that ta-C film is superior to a-C:H film in terms of corrosion resistance.

Properties of Diamond-Like Carbon Films Fabricated by the Filtered Cathodic Vacuum Arc Method

With the aim of evaluating the properties of diamond-like carbon (DLC) films, a comparison is made between tetrahedral amorphous carbon (ta-C) films fabricated by the double-bend-filtered cathodic vacuum arc (FCVA) method using no material gas and hydrogenerated amorphous carbon (a-C:H) films fabricated by the chemical vapor deposition (CVD) method using a hydrocarbon gas. It was found that the ta-C films are superior to the a-C:H films in terms of both wear resistance and combustion resistance. It was also determined that this superiority applies for ultra thin films as well.

Influence of temperature distribution along the junction plane on the lateral mode in AlGaAs phased array lasers

It is experimentally shown for the first time that far field lobe broadening, which is a multilateral mode operation under continuous wave operation in phased array lasers that emit diffraction limit beams under pulsed conditions mainly originates from temperature distribution along the junction plane. Spectrally resolved near field measurements show that pulse width, where broadening occurs, corresponds well to the one where temperature influence appears. Moreover, measurement of temperature distribution by the near field measurements and laser Raman spectroscopy show that a considerable temperature difference does exist between the center and edge elements in the array.

Crystal Growth of Laser Annealed Polycrystalline Silicon as a Function of Hydrogen Content of Precursors

The influence of hydrogen in a precursor on excimer laser crystallization behavior was investigated. The crystal orientation and lattice constant of polycrystalline silicon films were analyzed by X-ray diffraction measurement. An intensity ratio of 111 to 220 was used as an index of the (111) preferred orientation. A randomly oriented film with an index of 2 at lower energy density changed to the highly (111) oriented phase with an index of more than 15 at higher energy density. It was observed in the PE-CVD films that increasing the hydrogen in the precursor films decreased the orientation index. The lattice constant of the laser-annealed PE-CVD silicon was found to be larger than that of the PVD silicon and to decrease with an increase in laser energy density. The network structure of as-deposited PVD film with less hydrogen content was denser than that of as-deposited PE-CVD. The network structure of the precursor strongly affected the crystal growth, and the structure of the ELC poly-Si was still affected by the precursors, even though the hydrogen content decreased after laser annealing.

Degradation Modes Of High Power GaAlAs Infrared Lasers

Degradation modes of high power GaAlAs infrared lasers in accelerated life tests were investigated. Two modes were observed: gradual and rapid degradation. The latter degradation mode suddenly occurred after the gradual degradation mode. In order to clarify the cause of the rapid degradation, we compared them with artificially stressed degradation modes.

Thickness control of Ga1−xAlxAs layers grown by liquid phase epitaxy at low growth temperature

The uniformity of a Ga1−xAlxAs layer grown by liquid phase epitaxy was investigated as a function of the growth temperature in the range of 600 to 800°C. Lowering the growth temperature causes the growth rate to decrease, which contributes to remarkable reductions in both the normalized edge growth height (H) and the thickness variation (σ) over the wafer. At a growth temperature of 600°C, the flat Ga1−xAlxAs (solid composition, x = 0.45 ± 0.008) layer of 2.058 ± 0.07 μm (σ/d = 3.4%) can be obtained with an edge growth height of 2.92 μm (H = 1.25). On the other hand, at a short growth time of 0.3 s, the variation of layer thickness of less than ±0.007 μm (±8.9%) does not depend on the growth temperature. The probable lowest limit in a flat layer can be varied by the initial supersaturation.