Noriyuki Shige

Highly efficient (GaAl)As buried‐heterostructure lasers with buried optical guide

A new buried‐heterostructure laser with a buried optical guide has been developed. A threshold current around 20 mA and a differential quantum efficiency as high as 85% are obtained under cw operation. This results in highly efficient laser operation, i.e., 35% power conversion efficiency at an optical output of 15 mW per facet, at which no degradation is observed over 3000 h at room temperature. Stable lowest‐order transverse mode and nearly isotropic laser beam (∼25°×35°) are obtained. Second‐order harmonic distortion is 55–65 dB below the fundamental level for 30% modulation with a 100‐MHz sinusoidal signal at 5 mW.

Compositional separation of (Co-Cr-Pt)/Cr films for longitudinal recording and (Co-Cr)/Ti films for perpendicular recording

Compositional separation of (Co-Cr-Pt)/Cr films for longitudinal recording and (Co-Cr)/Ti films for perpendicular recording were examined by high resolution scanning electron microscopy (SEM) combined with selective chemical etching of the films using dilute aqua regia. A 150-nm-thick Co-Cr film over Ti underlayer for perpendicular recording was examined with this method. The CP (chrysanthemum-like pattern) structures (Maeda et al., 1986) due to the compositional separation were clearly observed. (Co-Cr-Pt)/Cr films for longitudinal recording were also examined. Even in this case, it was also possible to observe the compositional separation by SEM. The effects of sputtering condition on compositional separation and magnetic properties of (Co-Cr-Pt)/Cr films were investigated. >

Leaky‐mode buried‐heterostructure AlGaAs injection lasers

Leaky‐mode buried‐heterostructure injection lasers are fabricated and operated successfully under pulse bias at room temperature. The lasers consist of a thin active layer confined by parallel n‐ and p‐AlxGa1−xAs layers with a high mole fraction of AlAs (x=0.4) and perpendicular p−‐AlyGa1−yAs layers with a low mole fraction of AlAs (y=0.25). It is shown that most of the laser power can be coupled out into the low‐loss perpendicular layers and emitted from the end facets, resulting in highly collimated beams with a beam divergence of about 1°.

Stable operation of buried‐heterostructure Ga1−xAlxAs lasers during accelerated aging

The optical properties of buried‐heterostructure Ga1−xAlxAs lasers are carefully studied during accelerated aging at 70 °C. It is shown that neither kinks nor self‐pulsation is observed in the majority of the lasers after long‐term aging, in contrast to the observations in conventional stripe‐geometry lasers. The observed stable operation of buried‐heterostructure lasers may be attributed to the transverse‐mode stability and small cavity size intrinsic to the lasers.

Reduction of Threshold Current of Buried-Heterostructure Injection Lasers

Theoretical calculations of the threshold current of buried-heterostructure (BH) lasers are carried out. It is demonstrated that there is a current flow through the GaAlAs junction which does not contribute to the laser action. The current leaks through the GaAlAs junction in spite of the large difference between the saturation current density of the GaAlAs junction and that of the active region. The series resistance is shown to be responsible for this leakage current. Calculated threshold currents are shown to be in fairly good agreement with experimental results. For the reduction of the threshold current, several methods are presented. According to these guidelines, BH lasers which can operate in the mA range are realized.