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.

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Ultraviolet-C AlGaN resonant-cavity light-emitting diodes with top and bottom pipe-AlGaN-distributed Bragg reflectors (DBRs) have been demonstrated. For the top/bottom DBR structures, 20 pairs of n+-AlGaN:Si/n-AlGaN:Si stack structures were transformed into the pipe-AlGaN:Si/n-AlGaN:Si DBRs through a doping-selective electrochemical wet etching process. The reflectivity of the pipe-AlGaN DBR structure was measured as 90% at 276.7 nm with a 20.9 nm flat stopband width. The anisotropic optical properties of the pipe-AlGaN DBR structure had been analyzed through the polarization-dependent reflectance spectra. For temperature-dependent reflectance spectra, the central wavelengths were slightly redshifted from 275 nm (100 K) to 281 nm (600 K) due to thermal expansion, refractive index increase, and partial strain release phenomena in the pipe-DBR structure. High photoluminescence emission intensity and line-width reducing phenomena were observed at 10 K in the UVC-LED with the resonant-cavity structure, which has potential for high-efficiency UV-C light source applications.

Cavity mode-matching InGaN resonant-cavity light-emitting diodes (RC-LEDs) with aperture size-dependent emission have been demonstrated through nitrogen ion (N+) implantation and electrochemical wet etching processes. The RC-LED structure consisted of 570 nm-depth ion-implanted regions and an embedded 17-pair nanoporous-GaN/n-GaN distributed Bragg reflector (DBR) outside the aperture, while there existed a full 20-pair DBR structure within the aperture regions. Shorter and mode-matching cavity lengths were fabricated, confirmed by transmission electron microscopy and angle-resolved photoluminescence spectra inside the aperture area without subjecting to the N+ implantation. By reducing the aperture sizes, higher current density and narrower far-field electroluminescence emission patterns were observed in the RC-LED with an aperture size of 40 μm-diameter. These results demonstrate that the cavity mode-matching RC-LEDs with optical/electrical confinements and controllable cavity length mismatch features can be applied in a wide range of optoelectronic-based device applications.

Al0.12GaN/GaN membrane-type photodetectors (M-PD) were separated from the Si substrates through a chemical lift-off process. High photocurrent, low dark current, and high responsivity properties were observed in the M-PD structure compared to that on the Si substrate. Lattice-mismatch-induced tensile strain on the Al0.12GaN layer was enlarged in the M-PD structure and was analyzed by the photoluminescence and Raman spectra. From the simulation results, the energy band bending induced the potential barrier height at the AlN/air separated surface to deplete the surface states and suppress the leakage current. The strain in the AlGaN/GaN structures was manipulated by removing the Si substrate and roughening the AlN surface. The membrane-type ultraviolet photodetector consisted of the AlGaN/GaN two-dimensional electron gas channel and the large tensile strain at the Al0.12GaN layer, which can be used for high-efficiency optoelectronic applications.