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High-efficiency violet and blue InGaN microcavity light-emitting diodes

  • Author(s): Back, Joonho
  • Advisor(s): Nakamura, Shuji
  • et al.
Abstract

III-nitride materials are widely used these days for display, visual light communication, and power electronics from wearable devices to large home appliances. Especially, III-nitride micron-sized light-emitting diodes (µLEDs) in display get wide attentions because of its self-emissivity, small form factor and reliability. These characteristics make µLEDs as one of the best candidates for the next generation displays such as ultra-high resolution near-eye displays for augmented reality (AR) and virtual reality (VR) applications. Because µLEDs have advantages in lifetime, color gamut, form factor size and efficiency unlike the other displays, such as LCDs and OLED. However, there are several downsides of color mixing, color stability, and directionality for those purposes. The possible solution for those issues would be reducing the thickness of devices. This is basic concept of the microcavity LEDs (MC-LEDs). Therefore, it has been studied for improved directionality, spectrum purity, and thermal stability by minimizing the guided modes in the device. Recently, the ultra-short 200 nm cavity length MC-LEDs with the single mode operation was demonstrated by overcoming the fabrication limit. In this dissertation, the theory of MC-LED and its simulation are explained. Also, I am going to cover the whole processing steps and results of the electrically injected MC-LEDs grown on GaN semipolar (20-2-1) substrate. Continuously, the device improvement of using sidewall treatment has been achieved. While the previous device has 0.8% of external quantum efficiency (EQE), the second version has peak EQE of 7.3% without the encapsulation. Considering the EQE of the µLEDs without encapsulation is 10.5%, the sidewall treated MC-LEDs reach the similar performance level of conventional ones. This 205 nm MC-LEDs with the wavelength of 430 nm could produce better quality of display, because each device is separated and guided modes are negligible, which cause color mixing. Lastly, with well-designed epitaxial structure and processing steps, the record-thin MC-LEDs with cavity length of 113nm is achieved. We will cover the analysis of these MC-LEDs with different thicknesses, from 110 nm to 290 nm since the light extraction efficiency (LEE) and the directionality are determined by the cavity design in MC-LED. We will see a big potential to use these devices near future. The light can be well controlled by the thickness and active region position.

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