Date of Award:

2014

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Mechanical and Aerospace Engineering

Advisor/Chair:

Heng Ban

Co-Advisor/Chair:

Byard Wood

Abstract

Quantum cascade laser (QCL) diodes have potential applications in many areas including emissions analysis and explosives detection, but like many solid-state devices they suer from degraded performance at higher temperatures. To alleviate this drawback, the thermal properties of the QCL diodes must be better understood. Using molecular dynamics (MD) and photothermal radiometry (PTR), the thermal conductivity of a representative QCL diode is computed and measured respectively.

The MD results demonstrate that size eects are present in the simulated systems, but if these are accounted for by normalization to experimental results the thermal conductivity of the QCL can be reasonably obtained. The cross-plane conductivity is found to be in the range of 1.8 to 4.3 W=m K, while the in-plane results are in the range of 3.7 to 4.0 W=m K. These values compare well with experimental results from the literature for both QCL materials and for AlInAs and GaInAs, which the QCL is composed of. The cross-plane conductivity results are lower than those of either AlInAs or GaInAs, which demonstrates the phonon scattering at the interfaces. The in-plane results are between AlInAs and GaInAs, which is to be expected.

The PTR results are less concrete, as there seem to be heat transfer eects active in the samples which are not included in the models used to t the frequency scans. These effects are not 2D heat transfer artifacts nor are they the result of volumetric absorption. It is possible that they are the results of plasmon induction, but this is only supposition. As the data stand, the PTR and MD results are within an order of magnitude of each other and follow reasonable trends, which suggests that both results are not too far o from reality. While the experimental results are not entirely conclusive, the simulations and experiments corroborate each other suciently to warrant further investigation using these techniques. Additionally, the simulations present sucient internal consistency so as to be useful for thermal property investigation independent of the PTR results.

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Engineering Commons

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