UC Santa Barbara

The highly efficient blue InGaN-based light emitting diode (LED) has given rise to the solid-state lighting revolution, replacing its inefficient predecessors in home lighting, flashlights, displays, projectors, automotive lighting and much more. However, long-wavelength (green & red) InGaN-based LEDs have lagged in efficiency, often referred to as the ‘green gap’ in the LED industry. Addressing the green gap has become an increasingly important area of research for color-mixed home lighting and a wide range of display applications including AR and VR displays. Long-wavelength III-N LEDs have more non-radiative recombination and higher internal voltage barriers which hinder LED performance, especially the forward voltage and wall-plug efficiency (WPE).In the last decade, LED researchers have discovered that strategic use of V-defects (or V-pits) can help address these issues by creating energetically favorable pathways for carrier (electron and hole) transport. This novel approach to LEDs, makes use of the anisotropic electrical properties in III-N crystals by using c-plane for epitaxial growth and light emission and the {101 ̅1} plane (V-defect sidewall) for carrier transport. The lateral injection through the semipolar V-defect sidewalls reduces the polarization barriers and leads to reduced forward voltage and better WPE. In a few short years, V-defect approaches to green and red LEDs have been adopted by most major LED companies. In this work, we study the structure and formation of V-defects in LEDs grown by metal-organic chemical vapor deposition (MOCVD). Through advanced microscopy we investigate how V-defect structure, formation and density evolve in III-N epitaxial growth on (111) Si and sapphire. We demonstrate novel ways of forming V-defects and generating the threading dislocations that lead to V-defect nucleation. We also studied extended defects in LED active regions, their impact on LED efficiency, and provide experimental evidence of lateral injection through V-defects. We achieved high external quantum efficiencies of 6.5% in red LEDs and 30% in green LEDs grown on PSS with V-defect engineering. Furthermore, we show low voltage operation (2.8 V at 20 A/cm2) in green LEDs with V-defects. These results help provide a pathway to solving the green gap through V-defect engineering and advance the scientific understanding of V-defect formation and structure in III-N epitaxy.