Thermal resistance of heterostructure lasers

Abstract

A GaAs−GaAlAs heterostructure laser is modeled as a stripe heat source embedded in a layered structure, and an analytic expression is given for the steady−state thermal resistance 〈R〉 of the model. Over the range of typical layer thicknesses and conductivities, and for heat generated uniformly in the active region, 〈R〉 varies between 14 and 31 K/W for a 12×375−μ active region. Four types of heat sinks are shown to contribute an additional 3 to 10 K/W. Design implications are drawn for various properties including layer thicknesses, heat−sink and bond parameters, and radiative heat transfer by spontaneous emission. In disagreement with the common tacit assumption of a unique active−region temperature, it is found that about 40% of the temperature drop within the laser occurs in the active region (center to edge).