Multilayer thermionic cooling in semiconductor heterostructures

TL;DR: In this article, the authors studied the behavior of thermionic cooling in periodic barriers using 10-layer GaAs/AlxGal-xAs heterostructures and proposed a non-contact optical method that relies on the temperature dependence of features in the reflected spectrum of the devices.

Abstract: The feasibility of using semiconductor heterostructures as cooling devices is currently being studied. Utilising thermionic emission is proposed because of its potentially high cooling power. Multilayer devices have higher efficiency than single layers due to reduced phonon transport, or increased thermal resistance. We have studied the behaviour of thermionic cooling in periodic barriers using 10-layer GaAs/AlxGal-xAs heterostructures. Two methods of measuring cooling and heating are currently being investigated. Micro-thermocouples show temperature changes, but may affect readings because of their finite thermal mass. Also being investigated is the use of a non-contact optical method that relies on the temperature dependence of features in the reflected spectrum of the devices. Preliminary measurements have been carried out on direct band-gap bulk materials such as GaAs and InP and show strong temperature dependence. Cooling, either relative or absolute, has not yet been observed in our first generation devices. Any such cooling may be masked by joule heating in the comparatively large substrate on which the devices are built. Simulations are currently being carried out to determine where the most power is being dissipated in the devices. Introduction Thermionic refrigeration is based upon the principle of thermionic emission. That is, electrons are ejected from any hot surface. A voltage is used to sweep away energetic electrons ejected from the surface. As they leave they take energy with them and in doing so cool the surface. All thermionic devices are based upon Richardson's equation: