UC Santa Barbara

Despite the high efficiency and long development time of blue-emitting gallium nitride (GaN)-based μLEDs using metal-organic chemical vapor deposition (MOCVD) growth methods, high-performance devices emitting at the longer visible wavelengths have seen comparatively far less research and investment. Difficulties surrounding the growth of high-In layers by MOCVD makes device improvement increasingly difficult as the wavelength increases, requiring higher In content active regions, causing structural degradation and poor electrical performance. In this work, first higher power and efficiency of green-emitting LEDs is achieved through MOCVD design along with advanced characterization and device physics. Experimental results, modelling, and advanced design are employed in tandem to achieve higher power and lower operating forward voltage. The knowledge generated and advances made in the green LED design are then leveraged into realization of red-emitting InGaN/GaN μLEDs. Few examples of InGaN/GaN devices emitting in the red spectral regime currently exist with only a few realized proof of concept devices. Here, by employing semi-relaxed InGaN substrates, true red μLEDs using an InGaN growth structure can be achieved. Initially, a method to significantly improve material quality from the starting substrate is established, fully eliminating large-scale extended defects known as V-defects initially present in the substrate. On this newly improved material, red-emitting μLED devices with appreciable external quantum efficiency (EQE) can then be realized. Growth conditions in the active region and p-type regions are both thoroughly explored in order to increase light output power of the device and in turn improve EQE. These developments then finally result in realization of a red-emitting device nearing 1% peak EQE.