Limitations on standard procedure of determining internal loss and efficiency in quantum dot lasers

Limitations are discussed on the use in quantum dot (QD) lasers of the conventional method of determining internal loss coefficient alpha(int) and internal quantum efficiency eta(int) from a measured plot of the reciprocal slope efficiency versus the cavity length L. The limitations are imposed by the L-dependence of alpha(int) and eta(int) themselves. The effect of internal loss is quantitatively analyzed, which originates from the dependence of alpha(int) on the carrier density, with the latter being L-dependent. In short cavities, a plot of the reciprocal slope efficiency versus L can significantly deviate from a straight line, thus limiting the practicality of the standard procedure. For L longer than several hundred mu m, the limitations are strong in a single-QD-layer laser and moderate in a multiple-QD-layer laser. (c) 2006 American Institute of Physics.