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 (T 0=350–425 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 (∼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.

Injection lasers based on InAsGaAs and InGaAsGaAs quantum pyramids (QPs) with a lateral size ranging from 80 to 140 Å, are realized. 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 A cm−2) and ultrahigh characteristic temperatures (T0 = 350 to 425 K). For temperatures of operation above 100 to 130 K T0 decreases and the threshold current density increases (up to 0.95 to 3.3 kA cm−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 (80 to 140 Å) being close to ≈1.8 to 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 represents a three‐dimensional tetragonal array of InAs islands inserted in a GaAs matrix each composed of several vertically merging InAs parts. The first injection lasing in such an array is achieved.

InAs quantum dots (QDs) have been grown by metalorganic chemical vapor deposition on exactly (001) oriented GaAs using the Stranski-Krastanow growth mode. The samples exhibit a high average dot density of 4 ×1010 cm-2 with no defects over macroscopic areas. The QDs show bright room temperature luminescence at around 1.1 eV. Vertical dot stacks consisting of up to 5 QD sheets with various GaAs separation layer thicknesses have been produced. Transmission eletron microscope images show pronounced QD ordering in the growth direction. For thin separation layers the dot luminescence is red shifted by ∼ 70 meV for the stacked dots as compared to single dot sheets. A low threshold (100 A/cm2 at 77 K) separate confinement heterojunction laser with a five-fold dot stack as an active medium operating at up to room temperature is demonstrated.

We studied the transient behaviors of current-injection quantum-dot microdisk lasers at room temperature. Unique optical responses were observed, including the suppression of relaxation oscillations and fast turn-on. With the help of rate-equation modeling, the suppressed relaxation oscillations are attributed to the enhanced spontaneous emission factor in microdisk lasers. Short turn-on time, around 1 ns without pre-bias, results from the reduced carrier lifetime caused by the Purcell effect and increased nonradiative recombination rate due to higher surface/volume ratio. With short turn-on time, a large-signal direct modulation experiment at 1 Gbps is demonstrated. Modal transient behavior was also investigated under various temperatures from 100 to 300 K. Both of the transient lasing and steady-state lasing from side modes are suppressed at temperatures higher than 250K. Therefore, the quantum-dot microdisk lasers show the potential of single-mode operation under high-speed modulation at room temperature.

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