Long-wavelength InAs/GaAs quantum-dot laser diode monolithically grown on Ge substrate

The realization of semiconductor laser diodes on Si substrates would permit the creation of complex optoelectronic circuits, enabling chip-to-chip and system-to-system optical communications. Direct epitaxial growth of III-V semiconductor materials on Si or Ge is one of the most promising candidates for the fabrication of electrically pumped light sources on a Si platform. Here, we describe the first quantum-dot laser to be realized on a Ge substrate. To fabricate the laser, a single-domain GaAs buffer layer was first grown on the Ge substrate using the Ga prelayer technique. A long-wavelength InAs/GaAs quantum-dot structure was then fabricated on the high-quality GaAs buffer layer. Lasing at a wavelength of 1,305 nm with a low threshold current density of 55.2 A cm(-2) was observed under continuous-wave current drive at room temperature. The results suggest that long-wavelength InAs/GaAs quantum-dot lasers on Si substrates may be realized by epitaxial growth on Ge-on-Si substrates.