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This study presents the light-spectrum modification of warm white-light-emitting diodes (w-WLEDs) with 3D colloidal photonic crystals (3D CPhCs) to approximate candlelight. The study measures the angular-resolved transmission properties of the w-WLEDs with CPhCs, which exhibit photonic stop bands based on the CPhC photonic band structures. The w-WLEDs with 3D CPhCs produce a low correlated color temperature of 1963 K, a high color-rendering index of 85, and a luminous flux of 22.8 lm (four times that of a candle). This study presents the successful development of a novel low-cost technique to produce candlelight w-WLEDs for use as an indoor light source.

GaN-based ultraviolet photodiode with porous distributed Bragg reflectors (DBR) structure was demonstrated. The n +-AlGaN:Si epitaxial layers with high refractive index had been etched as porous-AlGaN layers with low refractive index through an electrochemical etched process. The peak wavelength of the responsivity spectra was measured at 355 nm, which was matched to the high reflectance wavelength region of the porous reflector. High photocurrent and large UV/visible rejection ratio were measured in the GaN photodiode with the porous-AlGaN reflector due to the light recycling process in the resonance cavity structure.

A porous-Al0.47GaN/n-Al0.47GaN stack structure with a large refractive index contrast has been fabricated through a homoepitaxial growth process on a Si-doped n+-Al0.47GaN/n-Al0.47GaN stack structure with a simple electrochemical wet etching process. A 20-pairs porous-Al0.47GaN distributed Bragg reflector structure (DBR) with a high aluminum content was fabricated at the deep-ultraviolet wavelength region of light emitting diodes. Low compressive strain and high reflectance has been observed in a porous-AlGaN/n-AlGaN DBR structure with 93% reflectivity at 276 nm. The high reflectance spectrum was measured at the 265 to 287 nm wavelength region in the porous AlGaN DBR structure. The absorption wavelength of the AlGaN layer was observed at about 250 nm, which is shorter than the high reflectance wavelength region of the porous DBR. Light extraction efficiency of the deep-UV optoelectronic devices can be improved by integrating the embedded porous AlGaN reflectors during the epitaxial growth process.

Polarization-dependent reflectance spectra of the pipe-GaN reflector show that it can be used as a polarized light source.