Analysis of TM/TE mode enhancement and droop reduction by a nanoporous n-AIGaN underlayer in a 290 nm UV-LED

A full structure 290 nm ultraviolet light emitting diode(UV-LED)with a nanoporous n-AlGaN underlayer was fabricated by top via hole formation followed by high-voltage electrochemical etching.The 20 to 120 nm nanopores were prepared in regular doped n-AlGaN by adjusting the etching voltage.The comparison between the Raman spectrum and the photoluminescence wavelength shows that the biaxial stress in the nanoporous material is obviously relaxed.The photoluminescence enhancement was found to be highly dependent on the size of the pores.It not only improves the extraction efficiency of top-emitting transverse-electric(TE)-mode photons but also greatly improves the efficiency of side emitting tran sverse-magnetic(TM)-mode photons.This leads to the polarization change of the side-emitting light from-0.08 to-0.242.The intensity of the electroluminescence was increased by 36.5%at 100 mA,and the efficiency droop at high current was found to decrease from 61%to 31%.

Realization of directional single-mode lasing by a GaN-based warped microring

Multimode and random directionalities are major issues restricting the application of whispering gallery mode microcavity lasers.We demonstrated a 40μm diameter microring with an off-centered embedded hole and warped geometry from strained III-nitride quantum well multilayers.Single-mode directional whispering gallery mode lasing was achieved by the warped structure and high-order mode suppression induced by the off-centered hole.In addition,the introduction of the off-centered hole reduced the lasing threshold from 3.24 to 2.79 MW/cm^(2) compared with the warped microdisk without an embedded hole while maintaining a high-quality factor of more than 4000.Directional light emission in 3D was achieved and attributed to the warped structure,which provides a vertical component of the light emission,making it promising for building multifunctional coherent light sources in optoelectronic integration.

Phosphor-free microLEDs with ultrafast and broadband features for visible light communications

Modulation bandwidth and the emission region are essential features for the widespread use of visible light communications(VLC).This paper addresses the contradictory requirements to achieve broadband and proposes ultrafast,asymmetric pyramids grown on adjacent deep concave holes via lateral overgrowth.Multicolor emission with an emission region between 420 nm and 600 nm is obtained by controlling the growth rate at different positions on the same face,which also can provide multiple subcarrier frequency points for the employment of wavelength division multiplexing technology.The spontaneous emission rate distinction is narrowed by lowering the number of the crystal plane,ensuring a high modulation bandwidth over broadband.More importantly,the residual stress and dislocation density were minimized by employing a patterned substrate,and lateral overgrowth resulted in a further enhancement of the recombination rate.Finally,the total modulation bandwidth of multiple subcarriers of the asymmetric pyramids is beyond GHz.These ultrafast,multicolor microLEDs are viable for application in VLC systems and may also enable applications for intelligent lighting and display.