Description
There is a growing interest in engineering control over not only electronic, but also phononic properties for novel types of optoelectronic devices, improved thermal management, as well as energy harvesting. Selection of enhanced phonon modes can be achieved using Bragg style reflectors tuned to the acoustic properties of the materials used. Recently it has been shown that so called adiabatic cavities where the reflectivity seen by phonons is more gradually increased offer potentially superior performance. Within the framework of the elastic continuum model, GaAs/AlAs aperiodic superlattices have been designed to adiabatically change the phonon mini gap parabolically at the zone centre in the reduced Brillouin scheme for target phonon modes of 100 GHz, 250 GHz, and 450 GHz. Additional samples were designed with linear and quartic variation in mini-gap, as well as purely Bragg reflector cavity structure. Samples were grown using molecular beam epitaxy according to the designs synthesized and ultrafast vibrational spectroscopy was used to observe and quantify the cavities phonon characteristics. Our results show evidence of strongly confined coherent acoustic phonons with discrete confined phonon levels in the studied phononic cavities, consistent with the target phonon modes. Focusing on the 100 GHZ design a strong coherent acoustic phonon confinement was seen for 96 GHz with a coherent lifetime greater than the phonon mode seen in the conventional distributed Bragg reflector type structures. Part of the motivation for developing phonon cavities is manipulating electron-phonon interaction to potentially control energy loss processes in energy conversion, we have studied the photoluminescence from the 100 GHz design and have seen evidence of elongated relaxation times for the photoexcited carriers. Discussion of these results as well as some potential designs for cavities realised in other materials systems will be discussed in the final presentation.
| I am the presenting author | Yes |
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