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The gain spectral characteristics of 1.5 µm wavelength GaInAsP/InP compressively-strained quantum-wire lasers with a wire width of 20 nm and 25 nm, fabricated by electron beam lithography and 2-step organometallic vapor phase epitaxial growth, were measured at a temperature of 100 K and were compared with those of quantum-film lasers fabricated on the same wafer. It was found for the first time that the material gain spectrum of quantum-wire lasers was narrower than that of the quantum-film laser.

GaInAsP/InP multiple-layered quantum-wire lasers with the wire width of 21 nm in the period of 100 nm were realized by CH 4 /H 2 reactive-ion etching followed by slight wet chemical etching and embedding growth by organometallic vapor phase epitaxy. A threshold current density as low as 1.45 kA/cm 2 was obtained with the cavity length of 980 µm. To our knowledge, this is the lowest value reported for 1.55 µm GaInAsP/InP quantum-wire lasers fabricated by the etching and regrowth method. Because of the temperature dependence of the lasing wavelength, a relatively large blue shift of 47 meV in the quantum-wire laser was observed, which can be attributed to not only a lateral quantum confinement effect but also a three-dimensional compressive strain effect. Finally, we improved the initial wafer structure in order to suppress over-etching of the active region, and obtained lasers consisting of a five-layered wirelike active region with good size uniformity (wire width of 42 nm, period of 120 nm). A threshold current density as low as 540 A/cm 2 was obtained with the cavity length of 1.38 mm.

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In order to suppress the occurrence of nonradiative recombination traps during an etching and regrowth process, whose origin was considered to be large latticemismatch, a partially strain-compensated five-quantum-well structure was used for 1.5 µm GaInAsP/InP lasers with wirelike active regions (wire widths of 43 nm and 70 nm) fabricated by electron beam lithography, CH4/H2 reactive-ion etching and organo-metallic vapor-phase-epitaxial regrowth. As a result, we realized wirelike lasers with wire widths of 43 nm with a threshold current lower than those of quantum film lasers prepared on the same wafer at temperatures up to 85°C, for the first time.