Current spread and overheating of high power laser bars

Abstract

The heating of a semiconductor laser bar imbedded between two heat spreaders has been studied theoretically and experimentally. The model included the p-cladding layer, active region, n-cladding layer, and n-substrate. Heat sources from the active region and both cladding layers were considered. An analytical relation was obtained between the temperature distribution in the laser and the bar geometry. The analytical approach revealed features that are usually missing in purely numerical modeling. It was shown that the current density across the active region is nonuniform, and that the magnitude of the nonuniformity grows when the resistance of the p-cladding layer decreases. This nonuniform current distribution can lead to higher temperatures at the edges of the laser stripe than in the middle. It was found that mutual heating of the individual lasers in the bar is controlled mainly by the overlap of the temperature fields in the heat spreaders. The theoretical results obtained without any fitting parameters show good agreement with the experimentally measured dependence of the active region temperature on pumping current.