Sub-wavelength GaN-based membrane high contrast grating reflectors

Abstract

The GaN-based membrane high contrast grating (HCG) reflectors have been fabricated and investigated. The structural parameters including grating periods, grating height, filling factors and air-gap height were calculated to realize high reflectivity spectra with broad bandwidth by the rigorous coupled-wave analysis and finite-difference time-domain method. Based on the optimized simulation results, the GaN-based membrane HCGs were fabricated by e-beam lithography and focused-ion beam process. The fabricated GaN-based membrane HCG reflectors revealed high reflectivity at 460 nm band with large stopband width of 60 nm in the TE polarization measured by using the micro-reflectivity spectrometer. The experimental results also showed a good agreement with simulated ones. We believe this study will be helpful for development of the GaN-based novel light emitting devices in the blue or UV region.

Subwavelength-thick lenses with high numerical apertures and large efficiency based on high-contrast transmitarrays

“…A novel approach is to use high-contrast gratings (HCGs), fabricated from semiconductors or high refractive index (highindex) dielectrics [17][18][19] , that can be designed with large reflection 20 or transmission 21 efficiencies. Wavefront control was originally achieved by rendering one dimensional gratings aperiodic by gradually modifying the local period and duty cycle of the grating [21][22][23] .…”

Progress and challenges in electrically pumped GaN-based VCSELs

“…A main challenge in the fabrication of a III-nitride-based HCG is to find a sacrificial layer that can be selectively removed without affecting the HCG layer. There have been a few attempts, such as bandgap-selective photoelectrochemical etching of a sacrificial InGaN superlattice to form an AlGaN HCG membrane 74 however, with a limited airgap height, and focused-ion-beam etching to create an airgap underneath a GaNbased HCG 75 , an impractical process for device integration on a wafer-scale. In addition, GaN membrane gratings have been fabricated from a GaN-on-Si structure [76][77][78] by selective etching of Si, and free-standing hafnium-oxide gratings using the same approach 79 , but applying this concept to fabricate a bottom mirror in a VCSEL is not straightforward, since growth of high-quality GaN on Si for laser applications is very challenging.…”

“…However much inferior performance has been achieved for GaN-based HCGs due to difficulties in this material system: there is no simple way to find a sacrificial layer with high wet etch selectivity to GaN. Attempts to realize III-nitride membrane type HCG structures for the visible regime have been limited to bandgap selective photoelectrochemical (PEC) etching of InGaN superlattices 74 , and focused-ion-beam (FIB) etching 75 , to make airgaps.…”

TiO2 membrane high-contrast grating reflectors for vertical-cavity light-emitters in the visible wavelength regime

“…A main challenge in the fabrication of a III-nitride-based HCG is to find a sacrificial layer that can be selectively removed without affecting the HCG layer. There have been a few attempts, such as bandgap-selective photoelectrochemical etching of a sacrificial InGaN superlattice to form an AlGaN HCG membrane, 9 however, with a limited airgap height, and focused-ion-beam etching to create an airgap underneath a GaN-based HCG, 10 an impractical process for device integration on a wafer-scale. In addition, GaN membrane gratings have been fabricated from a GaN-on-Si structure by selective etching of Si, [11][12][13] but applying this concept to fabricate a bottom mirror in a VCSEL is not straightforward, since growth of high-quality GaN on Si for laser applications is very challenging.…”