Bulk temperature mapping of broad area quantum dot lasers: modeling and micro-thermographic analysis

For novel devices such as quantum dot lasers, the usual thermal characterization using temperature induced wavelength shift is ineffective due to weak thermal shift of the inhomogeneously broadened gain-peak. This calls for new thermal characterization techniques for such devices. To this end we have analyzed bulk thermal properties of broad area quantum dot lasers theoretically, and have experimentally verified these calculations using the novel technique of microthermography. InGaAs/GaAs 950 nm emitting, 50 μm wide and 1.5 mm long, large optical cavity quantum dot lasers were used for the study. Our two-dimensional steady-state model self-consistently includes current spreading and distributed heat sources in the device and using finite element method reproduces high resolution temperature maps in the transverse cross section of the diode laser. A HgCdTe based thermocamera with detection spectral range 3.5-6.0 μm was employed for micro-thermography measurements. Its microscope with 6x magnification has a nominal spatial resolution of 4 μm/pixel for full frame images of 384×288 pixels. A ray tracing technique was used to model the propagation of thermal radiation inside the transparent laser die which in turn links calculated and experimentally derived temperature distributions. Excellent agreement was achieved which verifies the model-calculation and the thermal radiation propagation scheme inherent in the experimental approach. This result provides a novel means for determining reliable bulk temperature data from quantum dot lasers.