Current spreading and thermal effect in thin film Light Emitting Diodes for epitaxial lift off technology
The development of science and technology puts forward new requirements to electronic and optoelectronic semiconductor devices, such as flexibility, temperature and bio compatibility. Great advances in the technology of epitaxial lift off and transfer printing, have the potential to create new engineering opportunities and application possibilities for Light Emitting Diodes (LEDs) technologies. Researchers strive to make the device flexible and stretchable, so that it can be integrated into any surface, such as deformable display, wearable device, lighting and biomedical devices. In this paper, we utilize micro photoresist anchors to fabricate the two kinds of thin film LEDs, LEDs with strip electrodes and LEDs with square ring electrodes, respectively. Afterwards, we transfer them to the poly(dimethylsiloxane) (PDMS) succeeding in making flexible inorganic LEDs. We also test the electrical characteristics of TF LEDs to compare with the result of simulation. The current spreading and thermal effect are the key to the performance of thin film LEDs (TF LEDs) Using 2D finite element simulation, take recombination and lattice temperature effect on TF LEDs electrical characteristics into account, we analyze the current spreading in LED1 with strip electrodes and LED2 with square ring electrodes. We find that LED2s exhibit a better current distribution uniformity of TF LEDs and lower local highest temperature compared to LED1s in flexible substrates. Because of the improved current spreading and better thermal management, TF LEDs with square ring electrodes can work continuously under relatively large power without worrying about the damage caused by high temperature. This result has a guiding significance for the use of TF LEDs on flexible substrates.