High optical field confinement-possible silicon waveguides are used in various fields. The performance of a silicon waveguide depends on its sidewall roughness, which is responsible for scattering loss. The fabrication process for a silicon waveguide with a smooth sidewall for low loss was studied. The propagation loss of an optical silicon waveguide was reduced by using a SiO2 hard mask and reactive ion etching (RIE) with fluorine gases. The sidewall angle was controlled by Si etching with a SF6 and CF4 gas mixture. The thickness of the SiO2 hard mask affects the sidewall smoothing treatment. The roughness of the sidewall was reduced in the SiO2 etching process with a CF4 and O2 gas mixture as the thickness of the SiO2 hard mask was increased. The minimum propagation loss (0.89 dB cm−1) of the fabricated silicon waveguide was achieved by using the fabrication method introduced in this paper.

We report the first demonstration of room-temperature (RT) lasing at 1.3 µm from the ground state of three-stacked InAs quantum dots (QDs) in an In0.15Ga0.85As quantum well, which was grown by atomic layer epitaxy (ALE). For an as-cleaved device with a 2000-µm-long × 15-µm-wide ridge structure, the threshold current density (J th) at RT is 155 A/cm2 with the ground state lasing at 1310 nm under pulsed operation. The thermal coefficient of a lasing wavelength shift is 0.53 nm/K and the characteristic temperature is 103 K near RT. The lasing wavelength of the QD laser diodes (LDs) shows simultaneous lasing and the state switching from the ground state at 1310 nm and to the first excited state at 1232 nm with increasing injection current owing to the gain saturation of the ground state. The performance of ALE QD-LD is comparable to that of the conventional Stranski–Krastanov QD-LD.

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