The preparation of low current-threshold infra-red-visible (0.89-0.72 µm) AlxGa1-xAs/AlyGa1-yAs double-heterostructure lasers by molecular beam epitaxy

Room-temperature low current-threshold broad-area Fabry-Perot AlxGa1-xAs/AlyGa1-yAs double-heterostructure (DH) lasers have been prepared by molecular beam epitaxy (MBE) covering the lasing emission wavelength from 8900 Å to 7200 Å (infra-red-visible). In this emission range, the averaged pulsed current threshold densities, Jth, are as low as those obtained by liquid-phase epitaxy (LPE). At ∼ 8200 Å, the wavelength at which DH lasers have also been prepared by metalorganic chemical-vapor deposition (MO-CVD), the Jth´s of the MBE grown lasers are lower. For the best wafers grown, the averaged Jth´s are 800 A/cm², 1.0 kA/cm²and 2.8 kA/cm²(375µm × 200µm × 0.1-0.15µm) at ∼ 8800 Å, ∼ 8300 Å and ∼ 7200 Å, respectively. The importance of various growth conditions such as substrate-temperature and others for growing such low current-threshold DH lasers are studied. It is found that the Jthdecreases with increasing substrate-temperature from ∼ 450°C to ∼ 620°C. Laser wafers with lowest Jth´s are grown at substrate temperatures above ∼ 620°C. Regular proton-bombarded stripe-geometry lasers fabricated from GaAs-Al0.3Ga0.7As MBE DH wafers have CW threshold currents and total series resistances at least as low as those similar-geometry lasers grown by LPE. Averaged yields for such laser diodes of ≥ 90% were obtained in some wafers. Randomly picked diodes fabricated from an early MBE DH wafer having 0.4 µm GaAs active layer have operated continuously at a constant output power of ∼ 2 mW/mirror in a ∼ 38°C dry-nitrogen ambient for more than 7,000 h and still operating.