1.3-um InAs/GaAs quantum-dot lasers monolithically grown on Ge substrate

The realization of semiconductor laser diodes and light-emitting diodes on Si substrates would permit the creation of complex optoelectronic circuits for the first time, enabling chip-to-chip and system-to-system optical communications. Direct epitaxial growth of lll-V semiconductor materials on Si or Ge is one of the most promising candidates for fabricating electrically pumped light sources on a Si platform. Here, we describe the first quantum-dot laser diode 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 1305 nm with the extremely low threshold current density of 55.2 A/cm2 was observed under continuous-wave (CW) current drive at room temperature.