Anisotropic dependence of light extraction behavior on propagation path in AlGaN-based deep-ultraviolet light-emitting diodes.

The anisotropic extraction dependence of polarized light on propagation path in AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) is investigated by simulations and photoluminescence (PL) measurements. Theoretical calculations based on k⋅p approximation and Monte Carol ray tracing indicate that there are two kinds of polarized sources with different angular distributions in ~280 nm AlGaN-based LEDs, s-polarized (spherical-shaped) and p-polarized (dumbbell-shaped) sources, which have different extraction behaviors. It is found that the total light extraction intensities are improved with decreasing the propagation path, and the lateral surface extraction gradually becomes dominant. Moreover, the extraction intensity of s-polarized light improves more than that of p-polarized light when the propagation path decreases, leading to a greater polarization degree. Polarization-resolved PL measurements show that the polarization degree of extracted light from lateral facet of the AlGaN multiple quantum well sample can be enhanced from 1% to 17% as the average propagation path reduces by 0.6 mm, which is consistent with the simulation results of the anisotropic dependence of light extraction on propagation path. Our results are significant for understanding and modulating the anisotropic extraction behavior of polarized light to realize high efficiency AlGaN-based DUV LEDs.