Cavity-enhanced thermal emission from semiconductor lasers

Abstract

The thermal emission properties of GaAs-based semiconductor diode lasers are studied with a calibrated setup for quantitative measurements of spectrally resolved emittances. Emission spectra are measured for a stack of high-power diode-laser bars and for n-doped bulk GaAs reference samples and are compared to a calibrated blackbody radiator. The thermal radiation measurements are analyzed with a formalism providing the directional spectral emittance, transmittance, and reflectance under normal incidence. The thermal emission properties are related to the underlying materials properties such as absorption coefficients and carrier concentrations. The thermal emission from the semiconductor lasers displays a pronounced enhancement compared to the bulk reference samples. The metallic contacts and the heavily p-doped layers of the diodes are identified as the origin of this cavity enhancement. The semitransparent nature of the semiconductor materials influences the results of thermal infrared imaging substantially. We derive guidelines for extracting reliable information on device temperatures and discuss limitations of the technique.

Mechanisms and fast kinetics of the catastrophic optical damage (COD) in GaAs‐based diode lasers

“…Neither the lateral spatial resolution nor the 'information depth' meets the requirements defined in Sect. 3.1., mainly because of the low absorbance (emittance) of the (thin) heated surface region and huge background contributions [142,143]. Thermography has, however, been applied successfully for T bulk -analysis [144][145][146][147][148][149][150].…”

Thermoreflectance spectroscopy—Analysis of thermal processes in semiconductor lasers

“…Apart from the surface-probing thermometric techniques, thermal properties of the semiconductor laser were studied by IR imaging [13,[20][21][22][23][24] which provides fast information about temperature profiles and hot spot location, and wavelength tuning technique [25] which is used to determine the time resolved bulk temperature. These two techniques give information about bulk temperature, what is not a case for surface probing techniques.…”

Microthermography of diode lasers: The impact of light propagation on image formation

“…In Ref. 5 we determined ␣ ϳ 18 cm −1 for a typical laser structure with a n-type substrate doping of ϳ1.2ϫ 10 18 cm −3 . In Fig.…”

“…Such a calibration links the thermal emission power of the laser device as seen by the thermocamera to the corresponding temperature, without getting into determination of emittance of its semiconductor materials, which turns out to be quite involved. 5 Ray-tracing applies geometrical optics and material absorption to predict the trajectory and power of the light rays inside a linear medium. Without losing generality, monochromatic light of a wavelength of 5 m is used according to a weighted average over the detection range of our thermocamera system.…”

“…There, the spread of propagating thermal IR light is expected to alter the original thermal image of the semiconductor parts of optoelectronic devices at least on a microscopic scale on the order of 10-50 m. In addition, internal reflections at the metallic contacts, e.g., of diode lasers, result in a cavity enhancement of the thermal radiation as analyzed for extended devices and test samples in Ref. 5.…”