Feasibility of conventional method of extracting internal loss and internal quantum efficiency in edge-emitting quantum dot lasers

Abstract

Feasibility is discussed of the conventional method of determining internal loss coefficient and internal quantum efficiency from a measured plot of the reciprocal slope efficiency versus the cavity length L in semiconductor edge-emitting quantum dot (QD) lasers. The limitations are imposed by the cavity-length-dependence of internal loss and quantum efficiency themselves. The effect of internal loss is quantitatively analyzed, which originates from the dependence of internal loss on the carrier density, with the latter being L-dependent. In short cavities, a plot of the reciprocal slope efficiency versus the cavity length can significantly deviate from a straight line; particularly, the reciprocal slope efficiency increases with reducing the cavity length in short cavities. This plot asymptotically approaches an inclined line only in long cavities. Correspondingly, only infinitely-long-cavity (no mirror loss) values of the internal loss coefficient and the internal quantum efficiency can be extracted using the standard procedure. These latter differ significantly from those in short-cavity devices, thus strongly limiting the practicality of the procedure. For L longer than several hundred microns, the limitations are strong in a single-QD-layer laser and moderate in a multiple-QD-layer laser.