Heat-flux spreading in vertical-cavity surface-emitting lasers mounted substrate-down

Thermal resistance of vertical-cavity surface-emitting lasers (VCSELs) is one of the key parameters determining their CW performance. Its knowledge is essential in evaluating the potential of a particular VCSEL design for delivering high output power. Recently, we have proposed a simple approximate method for calculating thermal resistance of VCSELs using the concept of effective thermal conductivity. In that approach, a multilayer structure is replaced with a thermally equivalent homogeneous medium. In this paper, we present a new technique, based on previous analytical approximation, that allows for the first time one to consider multilayer aspects of heat conduction without involving extensive numerical calculations