Masahito Takusagawa

Degradations of Optically-Pumped GaAlAs Double Heterostructures at Elevated Temperatures

We have measured the growth of dark line defects (DLDs) under optical pumping and the gradual decrease in photoluminescence (PL) intensity of the active layer in GaAlAs double-heterostructure wafers at elevated temperatures. Two different velocities of DLDs are found which are considered to be dominated by α and β dislocations. A time lag is observed at the start of expansion of the DLDs. The activation energies of the velocity and the time lag are found to be 0.2 eV and 0.3 eV repectively. The velocity increases and the time lag decreases with increase in ΔX. The gradual degradation rate of the PL intensity of the active layer in optically-pumped samples is ten to a hundred times as large as that without optical pumping. The activation energy is calculated to be 0.6 eV for the former degradation rate and 0.8 eV for the latter degradation rate.

Lasing-Induced Change in the Differential Resistance of Stripe Geometry Ga1-xAlxAs DH Lasers

The lasing-induced change in the differential resistance is measured for various types of stripe geometry laser, and a model is given that explains the lasing induced change quantitatively to some extent. The amount of the lasing-induced reduction in the differential resistance is mainly determined by a parameter that limits the carrier supply into the active layer. The exsistence of a non-lasing region at the edge of the stripe and lateral carrier diffusion also decrease the amount of the reduction. In narrow-stripe lasers the amount of the reduction is small due to lateral carrier diffusion. From the moderate change in the differential resistance near the threshold, the spontaneous emission factor representing the contribution of the spontaneous emission to the lasing mode is estimated for various types of stripe laser.

Visible GaAlAs Laser with a Buried-Convex Waveguide Structure

A new buried-heterostructure visible GaAlAs laser, called a buried-convex waveguide structure (BCS) laser, has been developed. BCS lasers exhibit a highly stable transverse and single longitudinal mode operation in the 750 to 870 nm wavelength range. Very low threshold currents of 10–20 mA are obtained for the wavelength at about 750 nm. The output beam of BCS lasers has an aspect ratio of 2.0–2.5 and has no astigmatism. The relative intensity noise of BCS laser is very low at a level below -150 dB/Hz and is constant in the temperature range between 10 and 50°C. The maximum output power ofBCS lasers with facet coating is almost independent of the lasing wavelength between 750 and 870 nm.