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.
Highlights
Gallium nitride (GaN) materials have considerable in optoelectronic devices such as light-emitting diodes (LEDs), laser diodes (LD)[1], and vertical cavity surface emitting lasers (VCSEL)[2]
High reflectivity in the NP-distributed Bragg reflectors (DBR) was demonstrated which matched to the PL emission wavelength and the cavity length of the InGaN active layer
The effective cavity length, the penetration depth in NP-DBR structure, the InGaN active layer matched to a Fabry-Pérot mode, and the narrowing divergent angle were analyzed from the far-field PL radiative spectra
Summary
Gallium nitride (GaN) materials have considerable in optoelectronic devices such as light-emitting diodes (LEDs), laser diodes (LD)[1], and vertical cavity surface emitting lasers (VCSEL)[2]. Large lattice mismatch and low refractive index different of the stack structures are the challenges for the epitaxial DBR structures with long epitaxial growth time. The AlInN/GaN DBR structure[12,13] is lattice matched to GaN material, but the growth of AlInN layer remains a challenge in InGaN-based LED structures. To realize the high reflectivity with less pairs of stack structure, the air-gap/GaN DBR structures with large refractive index different had been fabricated through selectively anodized processe[14,15], and thermal decomposition techniques[16,17,18]. Nanoporous GaN material has been reported as an effective low refractive index for the DBR structure applications[21,22,23]. Optical and electrical properties of the InGaN LED structure with and without nanoporous DBR structure were analyzed in detail
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