Abstract
InGaN-based long-wavelength light-emitting diodes (LEDs) are indispensable components for the next-generation solid-state lighting industry. In this work, we introduce additional InGaN/GaN pre-wells in LED structure and investigate the influence on optoelectronic properties of yellow (~575 nm) LEDs. It is found that yellow LED with pre-wells exhibits a smaller blue shift, and a 2.2-fold increase in light output power and stronger photoluminescence (PL) intensity compared to yellow LED without pre-wells. The underlying mechanism is revealed by using Raman spectra, temperature-dependent PL, and X-ray diffraction. Benefiting from the pre-well structure, in-plane compressive stress is reduced, which effectively suppresses the quantum confined stark effect. Furthermore, the increased quantum efficiency is also related to deeper localized states with reduced non-radiative centers forming in multiple quantum wells grown on pre-wells. Our work demonstrates a comprehensive understanding of a pre-well structure for obtaining efficient LEDs towards long wavelengths.
Highlights
III-nitride emitters have attracted a lot of attention due to their advantages of energy savings, high brightness, and long lifetime
One of the main reasons arises from the strong piezoelectric field along the (0001) direction induced by the large lattice mismatch between sapphire substrate and epilayers
The light emitting diodes (LEDs) samples were grown on the patterned sapphire substrate (PSS) via metal organic chemical vapor deposition (MOCVD)
Summary
III-nitride emitters have attracted a lot of attention due to their advantages of energy savings, high brightness, and long lifetime. Though blue LEDs achieving a high external quantum efficiency [10], the emission efficiency is still limited in the long-wavelength region, which is commonly known as “greenyellow gap” phenomenon [2]. One of the main reasons arises from the strong piezoelectric field along the (0001) direction induced by the large lattice mismatch between sapphire substrate and epilayers. This built-in piezoelectric field gives rise to quantum-confined stark effect (QCSE) [11], which separates electron-hole wavefunctions and further degrades the radiative recombination efficiency. When the In content increases, QCSE becomes more severe, hindering the pursuit for efficient LEDs with long wavelengths
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