(Received October 23, 1995; accepted for publication November 21, 1995)
We have realized injection lasers based on InAs–GaAs and InGaAs–GaAs quantum pyramids (QPs) with a lateral size ranging from 80 to 140 Å. The structures with relatively small dots (∼80 Å) exhibit properties predicted earlier for quantum dot (QD) lasers such as low threshold current densities (below 100 Acm-2) and ultrahigh characteristic temperatures (T0=350–425 K). For operation temperatures above 100–130 K, T0 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 (∼140 Å) 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 Å being close 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.