Influence of the number of electronically coupled CdSe/ZnSe QD planes on characteristics of optically pumped green lasers

Structural properties and laser characteristics of true green (λ=530-550 nm) ZnSe-based optically pumped laser heterostructures with several (up to three) CdSe/ZnSe quantum dot (QD) planes in the active region were studied in details. Optimization of the MBE growth conditions to reduce the non-equilibrium defect density in the active region as well as the active region design allowed obtaining nearly the same rather low laser threshold values of Ithr∼4 kW/cm2 at Lcav∼100 μm for all the samples. The internal laser parameters were determined by measuring the laser threshold and differential quantum efficiency as functions of the cavity length. The design of laser structures provides high excitation homogeneity of the active region due to strong enough carrier tunneling between QD layers spaced by 5-nm-thick ZnSe barriers, which is confirmed by the sub-linear dependence of the transparency excitation intensity versus number of QD planes in the active region (IT = 0.556, 1.037, and 1.311 kW/cm2). The triple-QD-plane laser structure demonstrates significant increase in characteristic gain up to ΓG0=161.62 cm-1. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)