Lasing from excited states in self-assembled InP/GaInP quantum islands

Aiming at laser emission in the visible part of the spectrum, we have investigated the growth of self-assembled InP quantum dots on GaInP by low-pressure metal-organic vapour phase epitaxy using the Stranski–Krastanow growth mode. These InP islands show a photoluminescence emission energy of 1.72 eV (90 K) at low excitation densities. Lasing was observed on optically pumped laser structures with a single layer of InP dots, GaInP waveguide material and AlInP cladding layers above an excitation density of 1.3 kW cm−2 at 90 K. The detected laser line is located at 1.8 eV, about 80 meV higher than the ground-state transition energy. We attribute this behaviour to lasing from excited states in agreement with power-dependent photoluminescence experiments and photoluminescence excitation measurements, and gain measurements using the variable stripe length method. These laser structures show stimulated emission under optical pumping up to room temperature above excitation densities of 30 kW cm−2. Furthermore, injection lasers with Si- and Zn-doped (Al0.5Ga0.5)InP cladding layers have been realised where lasing occurred above a threshold current density of 290 A cm−2 with an emission line at 1.78–1.82 eV (90 K).