Session: 14-01: Measurement Techniques and Thermophysical Properties in Micro/Nanoscale

Paper Number: 132858

132858 - Quantitative Thermoreflectance Characterization of Quantum Cascade Laser Facets 

Abstract: 

Steady-state thermoreflectance uses a pump-probe approach to induce a steady-state temperature rise in a material, which is detected via a proportional change in surface reflectivity. This non-contact optical metrology technique has been used to accurately characterize the thermal properties of materials from nm-scale thin films to bulk over a wide range of thermal conductivities. Steady-state thermoreflectance provides a direct method for high-resolution characterization of the material or device material properties themselves, rather than an indirect analysis based purely on the relative surface temperature change (ΔT) or the transient of an electrically pumped device while in operation. By careful calibration of the system with a well-characterized material (in this case, high-purity fused silica), the proportional change of reflectivity with temperature dR/dT is calibrated and used to calculate the thermal conductivity point-by-point across a surface of interest. In this study, we apply this technique to the emitting facet of a quantum cascade laser.

Since their introduction roughly thirty years ago, large improvements have been made to increase the power, efficiency, and beam quality of quantum cascade lasers. Many of these improvements have been the result of material quality, laser design, and advances in packaging. However, as with many electronic and opto-electronic devices, thermal management is often the limiting factor in device performance. Many quantum cascade lasers, including the one in this study, require low-duty cycle, pulsed operation in order to increase peak power and avoid temporary or permanent thermal failure. Pulsed operation, however, is not desirable for many applications. Alternatively, in continuous-wave operation, the efficiency, output power, and threshold current are negatively affected by compounding thermal effects where phonon propagation is impeded by the multi-layer material and device design. To mitigate these effects, careful consideration must be given to the thermal properties of the materials used in the device epitaxy and fabrication process. However, it is often necessary to give preference to optical and electrical material characteristics of these materials to ensure functional devices. Therefore, a critical understanding of the thermal properties of the material stack of an as-fabricated device can be extremely beneficial for fully assessing the root cause of thermal limitations, as well as the effectiveness of retroactive thermal management strategies. 

In this work, we investigate the use of steady-state thermoreflectance as a largely unexplored method of material thermal conductivity evaluation for quantum cascade lasers. We demonstrate the effectiveness of this approach for quantitative, non-contact thermal characterization of post-fabrication quantum cascade laser epitaxy at the sub-micron scale. 

Presenting Author: Andrew Jones Laser Thermal

Presenting Author Biography: Andrew H. Jones is a research scientist at Laser Thermal, Inc. working in micro- and nano-scale thermal metrology, specifically in relation to semiconductor devices and thin films. He completed his Ph.D. and postdoctoral work at the University of Virginia in optoelectronics, specializing in photodetectors and avalanche photodiodes.

Authors:

Andrew Jones Laser Thermal
Brian Foley Laser Thermal
Jeremy Kirch University of Wisconsin-Madison
Shuqi Zhang University of Wisconsin-Madison
Dan Botez University of Wisconsin-Madison
Luke Mawst University of Wisconsin-Madison