We studied the development of V-shaped defects in GaInN±GaN quantum well superlattices. We observed that these defects could not be suppressed by varying growth parameters like strain, In content, GaInN growth temperature etc. However, perfect superlattices without such defects could be grown by cycling the temperature between low (for the GaInN wells) and high temperatures (for the GaN barriers). Although a large hydrogen/nitrogen ratio in the carrier gas seems to hinder the defect formation in GaN±AlGaN superlattices, it was not possible to suppress the defect formation in a GaInN±GaN superlattice by decreasing the total nitrogen flow.

Red-light-emitting quantum dot injection lasers have been prepared by solid-source molecular beam epitaxy. The separate confinement heterostructure contains densely stacked layers of self-assembled InP quantum dots embedded in Ga0.51In0.49P waveguide and Si/Be-doped Al0.53In0.47P cladding layers. Edge-emitting laser diodes are processed, which show quantum dot lasing at 90 K. Thereby, the threshold current density is 172 A/cm2. The energy of the laser line is at 1.757 eV, which is very close to the peak energy of subthreshold electroluminescence.

We report on threefold-stacked vertically aligned InP/GaInP quantum dot injection lasers emitting in the visible part of the spectrum (690–705 nm) with a low threshold current density of jth=172 A/cm2 at 90 K showing a thermally activated increase towards higher temperatures. We derived an activation energy for this behavior, which is found to be just one half of the energetic distance between the dot transition energy and the wetting layer band gap. Thus, we identify thermal evaporation of carriers out of the dots and into the wetting layer states as the process responsible for the increase in the threshold current. The nonradiative carrier lifetime in the wetting layer (τnrWL) is estimated to be approximately 250–400 ps.

No abstract

In this paper, we demonstrate the first injection lasers, using threefold-stacked vertically-aligned InP/GaInP quantum dots (QD's) as the active medium. The lasers emit in the visible part of the spectrum (690–710 nm) with a threshold current density (j th) of 172 A/cm2 at 90 K, increasing with temperature up to j th = 685 A/cm2 at 210 K. We identify the lasing being due to QD ground state transitions. The temperature dependence of j th is investigated in detail. At low temperatures, the threshold current density is almost independent of temperature while, towards higher temperatures, a thermally activated increase is found, strongly depending on QD size. The rise in j th is accompanied by a decrease of the integrated photoluminescence (PL) intensity, indicating that nonradiative recombination of carriers plays a significant role with increasing temperature. We assume thermal evaporation of carriers out of the dots and into the wetting layer (WL), where they recombine nonradiatively, to be the process responsible for the increase in j th.