Abstract
InGaN based resonant-cavity light-emitting diode (RC-LED) structures with an embedded porous-GaN/n-GaN distributed Bragg reflector (DBR) and a top dielectric Ta2O5/SiO2 DBR were demonstrated. GaN:Si epitaxial layers with high Si-doping concentration (n+-GaN:Si) in the 20-period n+-GaN/n-GaN stacked structure were transformed into a porous-GaN/n-GaN DBR structure through the doping-selective electrochemical wet etching process. The central wavelength and reflectivity were measured to be 434.3 nm and 98.5% for the porous DBR and to be 421.3 nm and 98.1% for the dielectric DBR. The effective 1λ cavity length at 432nm in the InGaN resonant-cavity consisted of a 30 nm-thick Ta2O5 spacer and a 148 nm-thick InGaN active layer that was analyzed from the angle-resolved photoluminescence (PL) spectra. In the optical pumping PL spectra, non-linear emission intensity and linewidths reducing effect, from 6.5 nm to 0.7 nm, were observed by varying the laser pumping power. Directional emission pattern and narrow linewidth were observed in the InGaN active layer with bottom porous DBR, top dielectric DBR, and the optimum spacer layer to match the short cavity structure.
Highlights
Nitride-based materials are widely used in optoelectronic devices such as lightemitting diodes (LEDs), laser diodes (LDs), and vertical cavity surface emitting lasers (VCSELs) [1,2]
All dielectric distributed Bragg reflector (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]
InGaN multiple-quantum wells (MQWs) layers was shown in Figure 1c as the epitaxial cavity structure above the porous DBR structure
Summary
Nitride-based materials are widely used in optoelectronic devices such as lightemitting diodes (LEDs), laser diodes (LDs), and vertical cavity surface emitting lasers (VCSELs) [1,2]. The VCSEL devices have low threshold current density, high efficiency, directional emission pattern, and the ability of high-speed operation properties for the high-density optical storage, biochemical sensors, and micro-projectors. For the shortwavelength VCSEL structures, the InGaN cavity length and the distributed Bragg reflectors (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] DBR 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]
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