| The Stranski-Krastanow growth mechanism of self-assembled InAs and InGaAs quantum dots on a GaAs substrate is examined. The atomic force microscopy (AFM) pictures show that the V/III ratio is the most important growth parameter in controlling the formation of three-dimensional islands, second only to the growth temperature. To adjust the arsine overpressure precisely on the epitaxial surface, a new gas switching sequence is designed and the use of hydrogen shroud flow as a means to change the surface kinetics is studied. With the new improved growth condition, InA quantum dot + quantum well lasers are demonstrated.; In order to achieve lower V/III ratio in material deposition, a new arsenic bubbler source, Tertiarybutylarsine (TBA), is installed. Further experimentation shows the photoluminescence of the discrete energy transitions of a layer of InGaAs quantum dots embedded in a GaAs waveguide with a wavelength as long as 1.219 μm with the use of submonolayer cycled deposition. However, the self-annealing effect is determined to be the major factor in limiting the realization of high-quality InGaAs QD lasers.; Data are presented showing that, besides the improvement in carrier collection, it is advantageous to locate strain-matching auxiliary InGaAs layers [quantum wells (QWs)] within tunneling distance of a single-quantum-dot (QD) layer of an AlGaAs-GaAs-InGaAs-InAs QD heterostructure laser to realize also smaller size QDs of greater density and uniformity. The QD density is changed from 2 × 1010/cm2 for a 50-Å GaAs coupling barrier (QW to QD) to 3 × 1010/cm2 for a 5-Å barrier. The improved QD density and uniformity, as well as improved carrier collection, make possible room-temperature continuous-wave (cw) QD + QW laser operation (a single InAs QD layer) at reasonable diode length (∼1 mm), current density 586 A/cm2, and wavelength 1057 nm. QW-assisted single-layer InAs QD laser, a QD + QW laser, is demonstrated that operates cw (300 K), and at diode length 150 μm in pulsed operation exhibits gain as high as ∼100 cm−1. The cw 300-K coupled InAs QD and InGaAs QW AlGaAs-GaAs-InGaA-InAs heterostructure lasers are grown by metalorganic chemical vapor deposition. |
