InAs-GaAs quantum pyramid lasers: In situ growth, radiative lifetimes and polarization properties

We have realized injection lasers based on InAs-GaAs and InGaAs-GaAs quantum pyramids (QPs) with a lateral size ranging from 80 to 140 Angstrom. The structures with relatively small dots (similar to 80 Angstrom) exhibit properties predicted earlier for quantum dot (QD) lasers such as low threshold current densities (below 100 Acm(-2)) and ultrahigh characteristic temperatures (T-0 = 350-435 K). For operation temperatures above 100-130 K, T-0 decreases and the threshold current density increases (up to 0.95-3.3 kAcm(-2) at room temperature) due to carrier evaporation from QPs. Larger InAs QPs (similar to 140 Angstrom) providing better carrier localization exhibit saturation of the ground-state emission and enhanced nonradiative recombination rate at high excitation densities. The radiative lifetime shows a weak dependence on the dot size in the range 80-140 Angstrom being close to similar to 1.8-2 ns, respectively. A significant decrease in radiative lifetime is realized in vertically coupled quantum dots formed by a QP shape-transformation effect. The final arrangement corresponds to a three-dimensional tetragonal array of InAs islands inserted in a GaAs matrix each composed of several vertically merging InAs parts. We achieved injection lasing in such an array for the first time.