Hironari Kuno

Compositional Dependence of Optical Constants and Microstructures of GeSbTe Thin Films for Compact-Disc-Rewritable (CD-RW) Readable with Conventional CD-ROM Drives

We studied the dependence of optical constants and microstructures of (GeTe)x(Sb2Te3)1-x films on composition to determine the optimal composition of phase change recording materials. The maximal differences in optical constants between crystalline and amorphous phases and the minimal crystalline grain sizes of the films were obtained at Ge39Sb10Te51. Using Ge39Sb10Te51 as a recording layer and TiO2 and SiO2 as interference layers, a compact disc rewritable (CD-RW) with 65% reflectivity and 60% modulation was obtained.

A quantum structure for high‐temperature operation of AlGaAs lasers: Multiple‐quantum barrier and multiple‐quantum well in active region

We propose a quantum structure of AlGaAs lasers designed for high‐temperature operation. In this design, the superlattice structure multiple‐quantum barrier (MQB) is located in the middle of active region which improves the injection efficiency of holes from the cladding into the active region, compared to MQB in cladding structure. Simulation results showed that low energy electrons can tunnel through the MQB barriers, while high energy electrons were reflected back by effective potential barrier to suppress the electron overflow from active to the cladding region. Multiple‐quantum wells (MQWs) are integrated at each side of MQB to minimize the overflow of tunneled electrons. A differential quantum efficiency change as small as 5% was achieved in the temperature range of 20–100 °C from MQB+MQW in active lasers.

X-Ray Topography Analysis of 4H-SiC Crystals Grown by the High-Temperature Gas Source Method

Synchrotron X-ray topography was carried out for 4H-SiC crystals grown by high-temperature gas source method, and transmission topography analysis with g= or 0004 was carried out for the cross-sectional samples. Dislocation contrasts extended in the growth direction were observed and the propagation behavior of threading screw dislocations (TSDs), threading edge dislocations (TEDs), basal plane dislocations (BPDs) and stacking faults (SFs) in the facet and step-flow regions were discussed. The propagation of dislocations in the fast grown crystal with a growth rate of 3.1mm/h was also evaluated by cross-sectional topography.

A new quantum structure ‘multiple quantum barrier and multiple quantum well in active region’ design for laser diode applications

Abstract A new quantum structure of AlGaAs laser for high temperature operation has been demonstrated. The new laser has a multiple-quantum barrier (MQB) structure located in the middle of the active region. This location of the MQB improves the efficiency of the hole injection into the active region compared to conventional MQB structure. It also maintains the suppressible effect of the electron overflow from the active region to the cladding layer. Moreover, multiple-quantum wells (MQWs) are integrated at each side of MQB to minimize the possible overflow of electrons by improving the recombination efficiency. The continuous-wave laser threshold current ( I th ) and the differential quantum efficiency ( η d ) have been improved about 50% by integration of MQW to the MQB in active laser. The I th as low as 31.1 mA ( η d : 0.44 mW/mA) was obtained on a ridge waveguide MQB + MQW in active laser of 4 μm wide and 300 μm long having as-cleaved uncoated facets.