Strained confinement layers in InP quantum dot lasers

We demonstrate lower temperature sensitivity at high temperature in a strained layer InP/AlGaInP self-assembled quantum dot design grown by MOVPE. The lasers emit between 700 - 730 nm, finding application in photodynamic therapies and bio-photonic sensing. We previously achieved a 300 K threshold current density of 150 Acm(-2) in similar structures for 2mm long lasers with as-cleaved facets, however at elevated temperatures J(th) increases rapidly with temperature. To address this issue we redesign the layers around the active regions, consisting of five layers of dots, each grown on a lower confining layer of (Al0.30Ga0.70)InP lattice matched to GaAs, formed from 3 mono-layers of InP and with a GaxIn(1-x)P upper confining layer. We grew two series of samples, x=0.43-0.58 with (Al0.70Ga0.30)(0.51)In0.49P waveguide claddings, and x=0.52-0.58 (AlInP claddings). Dot properties are strongly influenced by the UCL. Properties varied with Ga fraction. Measured absorption and lasing energies increase with Ga percentage, maintaining a constant separation from upper confining layer transition energies. A Ga fraction of x=0.54 (lightly tensile strained with respect to GaAs) gave the strongest and most well defined absorption, the lowest 300K J(th) for 2mm long broad area lasers (uncoated facets) of 180 Acm(-2) and lowest rate of J(th) increase with temperature.