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

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

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

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

High efficiency blue InGaN microcavity light-emitting diode with a 205???nm ultra-short cavity

High-efficiency blue InGaN-based semipolar (20-2-1) ultra-short microcavity light-emitting diodes (MC-LEDs) with a cavity length of 205 nm were demonstrated. A peak external quantum efficienc

Violet semipolar (20-2-1) InGaN microcavity light-emitting diode with a 200 nm ultra-short cavity length

International audienceViolet semipolar (20-2-1) InGaN microcavity light-emitting diodes (MC-LED) with a 200 nm ultra-short cavity length were demonstrated. The emission wavelength was 419 nm with a spectrum width of 20 nm. The external quantum efficiency (EQE) of MC-LED was constant at 0.8% for a forward current from 0.5 to 2 mA with the emitting area of 30×30 µm 2 . With increasing forward current, the peak wavelength and spectrum width of the emission showed almost no changes. For epitaxial growth, metal-organic chemical vapor deposition (MOCVD) was used. Substrate removal and tunnel-junction with an Ag-based electrode made possible the fabrication of the ultra-short 200 nm thick cavity MC-LED. This is more than a factor of 2 improvement compared to previous MC-LEDs of 450 nm cavity thickness sustaining 5 modes

Blue semipolar InGaN microcavity light-emitting diode with varying cavity lengths from 113 to 290 nm

Blue semipolar InGaN microcavity light-emitting diodes (MC-LEDs) with geometrical cavity lengths of 113, 205 and 290??nm were fabricated, demonstrating the feasibility of ultra-thin MC-LEDs. Precise positioning of the active layer in the cavity is shown to be possible. The peak external quantum efficiencies (EQEs) of 113??nm cavity length MC-LEDs with quantum well (QW) positions at 46%, 60% and 75% of the cavity height counted from the top of the device were 0.6%, 2.5% and 0%, respectively. The 113??nm cavity MC-LED with the QW position of 75% should have the highest light extraction efficiency of 35% but showed no emission due to a high leakage current caused by the device fabrication process. The 290??nm cavity length MC-LED had the highest peak EQE of 6.7%. The peak wavelength was almost constant at 430??nm at a current density from 289 to 1868 A??cm under pulsed operation

Long-Cavity M-Plane GaN-Based Vertical-Cavity Surface-Emitting Lasers with a Topside Monolithic Curved Mirror

We report long-cavity (60.5 λ) GaN-based vertical-cavity surface-emitting lasers with a topside monolithic GaN concave mirror, a buried tunnel junction current aperture, and a bottomside nanoporous GaN distributed Bragg reflector. Under pulsed operation, a VCSEL with a 9 µm aperture had a threshold current density of 6.6 kA/cm2, a differential efficiency of 0.7%, and a maximum output power of 290 µW for a lasing mode at 411 nm and a divergence angle of 8.4°. Under CW operation, the threshold current density increased to 7.3 kA/cm2, the differential efficiency decreased to 0.4%, and a peak output power of 130 µW was reached at a current density of 23 kA/cm2