Thermoreflectance study of facet heating in semiconductor lasers

We have developed new technique to monitor the facet heating in semiconductor lasers and to correlate these measurements with device performance and reliability. The method is based on thermoreflectance (TR), which is a modulation technique relaying on periodic facet temperature modulation induced by pulsed current supply of the laser. The periodic temperature change of the laser induces variation of the refractive index and consequently modulates probe beam reflectivity. The technique has a spatial resolution of about ∼1 μm and temperature resolution better than 1 K and can be used for temperature mapping over 300 μm×300 μm area. It can be applied to any kind of edge-emitting lasers or laser bars. This study also demonstrates that the thermal resistance of diode lasers can be accurately determined from the combined measurements of light – current, current – voltage characteristics and average junction temperature obtained by TR measurements. The thermal resistance together with the facet temperature maps can be used as an indicative parameter of the packaging and bond quality and is crucial for understanding device thermal behavior.