Material gain and two-state lasing in quantum well-dot lasers

Abstract

We report on modal and material gains as well as two-state lasing in lasers based on quantum well-dots (QWDs)–quantum heterostructures of mixed dimensionality (0D/2D). A high ground-state (GS) modal gain of 100 cm−1 is revealed in the device based on a single QWD layer. The upper limit of the GS material gain is estimated as 2.2 × 104 cm−1. In narrow-ridge 200 μm long lasers, pure GS lasing occurs up to a pumping current density that exceeds the threshold value by 17.5 times. A decrease in the optical confinement factor results in lasing via an excited state (ES) at a high pumping current. In the current range corresponding to the GS lasing, the devices operate in the transverse fundamental optical mode, whereas above the ES lasing threshold, they operate in the second order mode. In narrow-ridge lasers, the ES lasing is observed in longer cavities and at lower threshold current densities than in broad-area lasers.