# InGaN Resonant-Cavity Light-Emitting Diodes with Porous and Dielectric Reflectors  
[PERSON]  
1 Department of Materials Science and Engineering, Innovation and Development Center of Sustainable Agriculture, Research Center for sustainable energy and Nanotechnology, National Chung Hsing University, Taichung, 145 Xingda Rd., South Dist., Taichung City 402, Taiwan; [EMAIL_ADDRESS] (C.-J.W.); [EMAIL_ADDRESS] (Y.K.);  
(DBRs) should be considered. In short-wavelength VCSEL, the modulation of the cavity length may suppress the constructive interference, tune the directional far-field emission pattern, and affect the single-mode emission properties. The high reflectance of the embedded DBR structure can provide a high-quality factor of the lasing peak in the VCSEL devices. For the embedded DBR structures, the epitaxial AlGaN/GaN [3,4], AlN/GaN [5], and AlInN/GaN [6] DDR structures have been reported that have high reflectivity at the emission wavelength region of the InGaN active layers. All dielectric DBR VCSEL structures have been reported that are deposited on curved mirror of the sapphire substrate [7], on GaN after sapphire lift-off process [8], and as the epitaxial lateral overgrowth mirror [9]. The GaN VCSEL structure with bottom dielectric DBR and top TiO\({}_{2}\) high-index-contrast grating reflectors had been reported [10]. High efficiency InGaN VCSELs had been reported with the conductive AlInN/GaN DBR structures [11; 12; 13; 14]. For the current injection process, the VCSEL structure with buried tunnel junction had been demonstrated in the semi-polar blue GaN-based VCSEL [15]. The airgap DBR structure [16; 17] was incorporated into the VCSEL fabrication because of a high refractive index contrast between GaN and airgap in the stack structure. As for the epitaxial DBR structure, a large lattice mismatch and lengthy epitaxial growth time are the challenges to be solved. The porous-GaN/GaN stack structure with short epitaxial growth time and large refractive index difference had been reported as the DBR structures [18; 19; 20; 21] that were fabricated through a simple wet etching process. The lasing properties of the InGaN VCSELs with the porous-GaN DBR structures were reported [22; 23]. The mechanical [24], thermal [25], and electrical [23] properties of the InGaN devices with porous structures have been reported. The InGaN-based LED consisted of a 6\(\lambda\) cavity length and an embedded nanoporous DBR structure, without the top DBR structure, were reported in our previous report [26]. The single-mode and low threshold current density of the VCSEL devices can be realized in short 1\(\lambda\) resonant-cavity length. In the GaN-based VCSEL structure, 1\(\lambda\) cavity length is difficult to realize due to the large strain and the conductivity in the conventional AlGaN- and AlN-based DBR structures. A 1.5\(\lambda\)-cavity GaN-based vertical-cavity surface-emitting laser has been reported by using the n-type conducting AlInN/GaN DBR structure [11].  
In this paper, the optical confinement properties of 1\(\lambda\) InGaN resonant-cavity light-emitting diode (RC-LED) structure was studied by adding the top dielectric distributed Bragg reflector (DBR) and the bottom porous-DBR structure. Through the epitaxial growth and electrochemical wet etching processes, the InGaN active layer with an embedded 20-period porous-GaN/n-GaN DBR structure was demonstrated. Then, a Ta\({}_{2}\)O\({}_{5}\) spacer layer as a cavity length adjustable layer and 8.5-period Ta\({}_{2}\)O\({}_{5}\)/SiO\({}_{2}\) alternately stacked structure for top reflector were deposited on the InGaN epitaxial structure. The optical pumped lasing phenomenon at 432 nm was observed in the InGaN resonant cavity with 1\(\lambda\) effective cavity length by tuning the thickness of Ta\({}_{2}\)O\({}_{5}\) spacer layer. The surface morphology and optical properties of the InGaN resonant-cavity structures were analyzed in detail.