SUBJECT: Ph.D. Proposal Presentation
BY: David Rodin
TIME: Monday, April 23, 2018, 4:00 p.m.
PLACE: ES&T, L1105
TITLE: Developing Silicon-Based Thermoelectrics for Cooling Applications
COMMITTEE: Dr. Shannon Yee, Chair (ME)
Dr. Zhuomin Zhang (ME)
Dr. Samuel Graham (ME)
Dr. Satish Kumar (ME)
Dr. Martin Maldovan (ChBE)


Research on silicon thermoelectric coolers lies at the intersection of semiconductor physics, nanoscale heat transfer, industrial manufacturing, and device engineering. The electronic properties of doped silicon (σ≈100,000 S/m and S≈200 µV/K at 10^20 cm-3) are highly desirable, but the intrinsic thermal conductivity is at least two orders of magnitude too high for thermoelectric applications. The phononic contributions to the thermal conductivity dominate in silicon and have mean free paths that span a wide range of length scales at room temperature. Conversely, electronic contributions to the thermal conductivity span a much narrower mean free path spectrum at smaller length scales. The thermoelectric potential of bulk silicon may be realized in nanoporous silicon (np-Si) that selectively impedes phonons. The task of minimizing thermal conduction, without significantly affecting the electronic transport, represents an opportunity to use recent scientific understanding of thermal transport in silicon for the important engineering application of cooling. Furthermore, the development of np-Si creates an opportunity for experimental measurements that may further the scientific understanding of nanoscale physics. This proposal will detail (i) efforts to develop measurement techniques that can directly observe phonon transport in silicon, (ii) the current state of np-Si fabrication process, (iii) pressure-dependent thermal conductivity measurement results for np-Si, and (iv) preliminary results from numerical models that use existing phonon models to predict the thermal conductivity of np-Si. This work will also propose several studies with the goal of using np-Si to further scientific understanding of phonon transport in silicon.