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1.
Sci Rep ; 7(1): 4968, 2017 07 10.
Article in English | MEDLINE | ID: mdl-28694493

ABSTRACT

A GaN/AlGaN ultraviolet light emitting diode (UV-LED) structure with a porous AlGaN reflector structure has been demonstrated. Inside the UV-LED, the n+-AlGaN/undoped-AlGaN stack structure was transformed into a porous-AlGaN/undoped-AlGaN stack structure through a doping-selective electrochemical etching process. The reflectivity of the porous AlGaN reflector was 93% at 374 nm with a stop-bandwidth of 35 nm. In an angle-dependent reflectance measurement, the central wavelength of the porous AlGaN reflector had blueshift phenomenon by increasing light-incident angle from 10° to 50°. A cut-off wavelength was observed at 349 nm due to the material absorption of the porous-AlGaN/u-AlGaN stack structure. In the treated UV-LED structure, the photoluminescence emission wavelength was measured at 362 nm with a 106° divergent angle covered by the porous-AlGaN reflector. The light output power of the treated UV-LED structure was higher than that of the non-treated UV-LED structure due to the high light reflectance on the embedded porous AlGaN reflector.

2.
Sci Rep ; 6: 29138, 2016 07 01.
Article in English | MEDLINE | ID: mdl-27363290

ABSTRACT

InGaN light emitting diodes (LED) structure with an embedded 1/4λ-stack nanoporous-GaN/undoped-GaN distributed Bragg reflectors (DBR) structure have been demonstrated. Si-heavily doped GaN epitaxial layers (n(+)-GaN) in the 12-period n(+)-GaN/u-GaN stack structure are transformed into low refractive index nanoporous GaN structure through the doping-selective electrochemical wet etching process. The central wavelength of the nanoporous DBR structure was located at 442.3 nm with a 57 nm linewidth and a 97.1% peak reflectivity. The effective cavity length (6.0λ), the effective penetration depth (278 nm) in the nanoporous DBR structure, and InGaN active layer matching to Fabry-Pérot mode order 12 were observed in the far-field photoluminescence radiative spectra. High electroluminescence emission intensity and line-width narrowing effect were measured in the DBR-LED compared with the non-treated LED structure. Non-linear emission intensity and line-width reducing effect, from 11.8 nm to 0.73 nm, were observed by increasing the laser excited power. Resonant cavity effect was observed in the InGaN LED with bottom nanoporous-DBR and top GaN/air interface.

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