Degradation of High-Power UVC Light-Emitting Diodes via Emission-Activated Nitrogen Vacancy Generation

Abstract

We reported an unexpected power degradation mechanism in high-power ultraviolet C (UVC) light-emitting diodes (LEDs) grown on high-quality AlN templates. The LED underwent an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> = 350 mA stress for 250 h. After stress, the output power under <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> = 350 mA degraded by 65%. Although the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> curve and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> curve measurements suggested a strong carrier leakage, the electroluminescence (EL) spectrum did not suggest any significant crystal quality degradation in the active region. Cross-sectional transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) mapping revealed new defects nucleated and propagated from the p-GaN/electron blocking layer (EBL) interface. An observable nitrogen loss was introduced to the p-GaN contact layer under EDS. We inferred that the nitrogen desorption was activated by the UVC photon emitted from the active region. The nitrogen vacancies created a continuous leakage path from the active region to the p-electrode via various trap-assisted transport mechanisms.