Effective Interface Engineering for Phonon Manipulation in Multi-Layered Semiconductor Systems

Effective thermal management in functional devices has become more and more important as the demands on device performance keep increasing continuously [1]. Interfaces are crucial to device functionality. However, they could inevitably cause heat accumulation. So, it is essential to be able to manipulate the thermal transport through interface engineering. The semiconductor/semiconductor and metal/semiconductor interfaces are two types of important interfaces in the study of thermal transport, especially in semiconductor devices. The change of interface structure is bound to affect its transport properties. Therefore, it is expected that the regulation of phonon transport behavior can be realized through the design of unique multi-layered structures and utilization of effective interface engineering.<br/><br/>In this work, we have designed a series of multi-layered semiconductor structures and grown them using molecular beam epitaxy (MBE). Owing to the atomic-level control of growth, MBE offers us more freedom to realize high quality multi-layered samples with delicate structural parameters, including single monolayered superlattices. Manipulation of long-wavelength phonons is especially important for these structures as their developments continue to pursue the limit of thermal conductivity. Here, the experimental demonstration of manipulating and probing long-wavelength phonon thermal transport in Al_xGa_1-xAs/Al_yGa_1-yAs and InAs/AlAs superlattices will be reported. A direct experimental approach is demonstrated to probe and monitor the contribution of long-wavelength phonons to the thermal conductivity, based on the quasi-ballistic transport principle of phonons. In addition, we have observed evidence of coherent phonon transport up to 500 K. Effective interface manipulation in some artificial metal/semiconductor interfaces will be presented and discussed too. This demonstration holds the very promise to be a universal strategy for manipulating and probing phonon thermal transport in various application scenarios, including microelectronics, thermoelectrics, and optoelectronics.<br/><br/>[1] D. G. Cahill, P. V. Braun, G. Chen, D. R. Clarke, S. Fan, K. E. Goodson, P. Keblinski, W. P. King, G. D. Mahan, A. Majumdar, Nanoscale thermal transport II, Appl. Phys. Rev. 1 (2014) 011305.