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GaAs/AlGaAs graded-index, separate confinement heterostructure quantum-well lasers with an extremely low threshold current density (J th) were grown by molecular beam epitaxy on 0.5° misoriented (111)B substrates. The J th of these lasers was reduced by 20 A/cm2 compared with that of (100)-oriented devices, which results from the quantization along the <111> direction. The minimum J th of 158 A/cm2 was achieved for a 490 µm long device.

Self-oscillations of V-channeled substrate inner stripe (VSIS) lasers with index guiding and the influence of external feedback on low-frequency noise generation are presented. The self-oscillation is induced by means of shortening a cavity length of VSIS laser to 110 μm. VSIS lasers with self-oscillation have the fundamental linewidth of 0.56 Å below 3 mW and are not sensitive to both phase and amplitude of the externally reflected light. Signal to noise ratio of short-cavity VSIS laser at 1 MHz with a 10-KHz bandwidth was 97 dB at 0.05% optical feedback.

Fundamental characteristics of (111) oriented GaAs/AlGaAs graded-index separate-confinement-heterostructure single quantum well lasers have been compared with conventional (100) oriented lasers. In particular, the threshold current density Jth of (111) oriented lasers does not change with the well width Lz in the range of Lz=30–100 Å, which corresponds to an ideal extreme. The lowest Jth of 145 A/cm2 together with a high characteristic temperature T0 of 186 K in the threshold-temperature dependence has been achieved for an Lz of 40 Å and a cavity length of 490 μm. The dependence of T0 on Lz showed that T0 is maximum at Lz∼60 Å for both (111) and (100) oriented lasers.

We applied the technique of ammonium sulfide treatment to Al x Ga1-x As (110) surfaces and investigated the atomic composition of a surface by Auger electron spectroscopy and X-ray photoelectron spectroscopy. It was found that surface oxidation was significantly reduced by the sulfur treatment and that sulfur atoms were mainly bonded to Al atoms in an Al-enriched sample of Al x Ga1-x As (x=0.78). The surface compositions of the Al-enriched specimen (x=0.43, 0.78) were also found to be As-riched as a result of both sulfur treatment and the preferential etching of metallic atoms by an acidic solution, which prevents the initial oxidation of the surface of Al x Ga1-x As.