Photonic crystal enhanced LED for electroluminescence cooling

• Main Author: Li, Zheng, Ph. D. Massachusetts Institute of Technology
• Other Authors: Rajeev Ram.
• Format: Others
• Language: English
• Published: Massachusetts Institute of Technology 2017
• Subjects: Materials Science and Engineering.
• Online Access: http://hdl.handle.net/1721.1/108997

Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017. === Cataloged from PDF version of thesis. === Includes bibliographical references (pages 97-102). === An light-emitting diode (LED) consumes low-entropy electrical power and emits incoherent photons. In this process, the lattice heat also contributes to the output power if the LED operates at voltages below the photon energy (qV < h[omega]). Therefore, an LED can potentially cool itself, and the phenomenon is referred to as electroluminescence cooling (ELC). Although researchers recently reported LEDs with net cooling in various wavelength, the cooling power was not sufficient to compensate the heat flux from the ambient and thus no temperature drop is observed. In this thesis, we design and fabricate a photonic crystal (PhC) enhanced unencapsulated LED for direct observation of ELC. The PhC pattern and the structure of the device are optimized to achieve approximately 76% extraction efficiency and 300 [mu]W/cm2 net cooling power. The LED is designed to have smaller surface area and thermal mass compared to an encapsulated one to eliminate overwhelming convection heat flux. According to our thermal models, such an LED should exhibit temperature by 0.1 K and 0.5 K in air and vacuum, respectively. We also present preliminary fabrication processes and results. The critical steps include a flip-chip process with metal-metal bonding, substrate etching, and interference lithography for the PhC pattern. === by Zheng Li. === S.M.