# InGaN Resonant-Cavity Light-Emitting Diodes with Porous and Dielectric Reflectors
## 2 Materials and Methods  
InGaN RC-LED structures were grown on a 4 in. c-face (0001) patterned sapphire substrate by using the metal-organic chemical vapor deposition (MOCVD) system. Trimethyl-gallium (TMGa), ammonia (NH3) gas, and trimethylindium (TMIn) were used as gallium (Ga), nitrogen (N), and indium (In) sources material, respectively. Silane (SiH\({}_{4}\)) and bis-cyclopentadienyl magnesium (CP2 Mg) were used as the n-type and p-type doping sources, respectively. The LED epitaxial layers consisted of a 30 nm-thick GaN buffer layer, a 4.0 \(\upmu\)m-thick unintentionally doped GaN layer, 20-period n\({}^{+}\)-GaN:Si/n-GaN:Si (55 nm/45 nm) stacked structure, a 38 nm-thick n-GaN layer, 5-period In\({}_{0.2}\)GaN/GaN (3 nm/9 nm) multiple-quantum wells (MQWs) structure, and a 50 nm-thick p-GaN layer. The growth temperatures of the GaN buffer layer and the u-GaN layer were measured at 530 \({}^{\circ}\)C and 1050 \({}^{\circ}\)C, respectively. The Si-doping concentrations of the stacked structure were measured at 2 \(\times\) 10\({}^{19}\) cm\({}^{-3}\) for the n\({}^{+}\)-GaN:Si layer and at 2 \(\times\) 10\({}^{18}\) cm\({}^{-3}\) for the n-GaN:Si layer, respectively, at 1050 \({}^{\circ}\)C. The growth temperature and Si-doping concentration of the n-GaN layer were measured at 1050 \({}^{\circ}\)C and 2 \(\times\) 10\({}^{18}\) cm\({}^{-3}\), respectively. The growth temperature of the InGaN/GaN MQW active layer was measured at 760 \({}^{\circ}\)C. The growth temperature and Mg-doping concentration of the p-GaN layer were measured at 950 \({}^{\circ}\)C and 1 \(\times\) 10\({}^{18}\) cm\({}^{-3}\), respectively. The p-type GaN:Mg layers were thermally activated in the furnace at 750 \({}^{\circ}\)C for 30 min in N\({}_{2}\) ambient gas. The lateral wet etching channels with a spacing of 230 \(\upmu\)m on the LED structure were defined through the laser scribing (LS) process. The depth of LS line was measured at 2.2 \(\upmu\)m to reach the as-grown 20-period n\({}^{+}\)-GaN:Si/n-GaN stacked structure by using 355 nm pulsed laser. The Indium metal contact was used to contact the n\({}^{+}\)-GaN:Si layer to apply the positive bias during the wet etching process. Then, the samples were cleaned through the ultrasonic cleaning process in the deionized water and the isopropyl alcohol (IPA) solution to remove the contamination in the etching channels. After the wet etching process, the n\({}^{+}\)-GaN:Si layers were transformed into porous GaN layers through the doping-selective electrochemical etching process in a 0.5 M nitride acid solution with a positive 8 V external bias voltage. The EC-treated samples were rinsed in the deionized water and dried for the following measurements. The GaN EC etching porosification chemistry/process have been reported [16; 27]. Then, high refractive index n\({}^{+}\)-GaN:Si layers were transformed into low refractive index of porous GaN layers. The treated DBR structure consisted of a quarter-wavelength porous GaN layers and a quarter-wavelength GaN layers acted as a bottom reflector. Then, a 30 nm-thick Ta\({}_{2}\)O\({}_{5}\) film was deposited on the top of the p-type GaN:Mg layer acting as a spacer layer for tuning the cavity length in the resonant-cavity structure. Finally, the 8.5-period Ta\({}_{2}\)O\({}_{5}\)/SiO\({}_{2}\) dielectric DBR was deposited onto the Ta\({}_{2}\)O\({}_{5}\) spacer layer to complete the full RC-LED structure for optical measurement. The non-treated LED structure was defined as the standard LED (ST-LED). The InGaN LED with top and bottom DBR structure was defined as the resonant cavity LED (RC-LED). The photoluminescence spectra were measured by using monochromators (JOBIN YVON iHR550) with a TE-cooled charge-coupled device (CCD) detector. The surface morphologies of the RC-LED structures were observed using the optical microscope (OM) and the field-emission scanning electron microscope (FE-SEM, JEOL 6700F).