Thermoelectric coolers are rapidly becoming a viable alternative to conventional vapor-compression (household) refrigerators due to their comparable efficiency, smaller size/weight, and higher reliability. In addition, thermoelectric coolers have the capability to be scaled down in size to cool small devices such as integrated circuits, and can be operated reversibly to generate electrical power from a heat source. The metric used to quantify the efficiency of a thermoelectric material is the figure-of-merit ZT, which for the best thermoelectric materials has remained nearly constant at ZT=1 for the last 50 years. In the last several years, however, research into nanostructured materials that have specially-tailored properties has demonstrated ZT values of more than 2. In this work, we will explore a new effect that has recently been shown to increase thermoelectric performance at the nanoscale. Measurements indicate that simple diode structures (a basic building block of electronic devices) have strong thermoelectric effects near the internal semiconductor bipolar junction that defines the device. We will take advantage of this effect by creating a nanostructured thermoelectric material in which bipolar junctions are interspersed throughout the material at interfaces with quantum dots, causing a net increase in the thermoelectric performance of the material. We will use several methods to measure how the presence of these quantum dot bipolar junctions affects thermoelectric properties on a nanometer scale as well as how they affect the overall ZT of the material.
