Reduction of crystal defects in active layers of GaAs-AlGaAs double-heterostructure lasers for long-life operation

The influence of oxygen in ambient gas during liquid-phase epitaxial growth on a double-heterostructure (DH) wafer is investigated. The oxygen incorporated into grown layers seems to be associated with the formation of crystal defects such as so-called dark-spot defects (DSD's) and saucer pits. When the oxygen concentration is reduced less than 0.03 ppm, crystal defects such as DSD's and saucer pits drastically decrease in the epitaxial layers. Al added into Ga solutions behaves as the getter of the oxygen in the Ga solutions and prevents the formation of DSD's in the active layers. The correlation between DSD's and etch pits is examined. All of the dislocations do not always contribute to the formation of DSD's. The formation of DSD's depends on oxygen concentration in the ambient hydrogen gas. In DH lasers fabricated from DH wafers grown under the extremely low oxygen concentration, the operating life at room temperature exceeds 10 000 h at the present time.