GaN Gratings Research Articles

Interfacial Control of ZnO Microrod for Whispering Gallery Mode Lasing

Energy loss control at interfacial areas is a significant issue to improve the optical performance of hybrid optical resonant cavities. In this work, we analyzed the simulated electric field intensity to predict the optical loss or gain in ZnO microrod cavity interfaced with both pristine and Al nanoparticles decorated GaN gratings. A single ZnO microrod was placed on GaN gratings to compose three interfacial configurations, these are, ZnO/Air, ZnO/GaN, and ZnO/Al/GaN, their lasing behaviors were investigated experimentally. Experimental results indicate that the lasing intensity, threshold power, and quality factor all depend on interfacial gain and loss. Through introducing the localized surface plasmon resonance (LSPR) of Al nanoparticles at interface areas, improved lasing performance was observed for the ZnO/Al/GaN hybrid structure. Furthermore, the LSPR coupling mechanism responsible for the observed lasing improvement was revealed by the scanning near-field optical microscopy (SNOM) and time-resolv...

Etch tapered angle on the influence of GaN membrane grating reflectance spectra

The technique of backside thinning is used to obtain thinner freestanding GaN membrane. This technique is helpful for producing stronger reflectance peaks and to reduce the reflectance spectra quantity and reflectance interference in the visible light range. Ion beam etching (IBE) was used to fabricate a GaN membrane grating, and the size of the tapered angle of which has an important affect on the reflectance spectra modes. Therefore, we presented a GaN membrane grating model with tapered angle which is built based on a GaN-on-silicon wafer structure. The influence of the varied tapered angle on the reflectance spectra of grating was investigated. Meanwhile, affects of different parameters like the grating thickness, membrane thickness, grating period, filling factor, incident beam based on a certain tapered angle were also analyzed on reflectance spectra of the GaN grating. Rigorous coupled wave analysis (RCWA) was used as theoretical principle for numerical simulations on the GaN grating model in this study. The results of this report are very useful for fabricating GaN reflectance photonic devices, such as refractive index sensor, couplers and so on.

Guided-Mode Resonances in GaN Membrane Grating

This paper proposes guided-mode resonant GaN grating that are implemented on a GaN-on-silicon wafer structure. Numerical simulations based on rigorous coupled wave analysis (RCWA) are performed to model multiple resonances in thick GaN membranes. Back wafer etching of freestanding GaN membranes is used as a tuning mechanism to manipulate the optical performance in the visible wavelength range. Angular resolved micro reflectance measurements are conducted to characterize the fabricated GaN gratings and show the dependence of guided-mode resonances on the filling factor of the gratings, the membrane thickness, and the polarization of incident beam. The experimental results agree well with numerical simulations. This paper opens the way to fabricate guided-mode resonant GaN grating for many diverse applications.

Circular GaN Membrane Gratings

This letter presents the fabrication and characterization of freestanding circular GaN gratings on a GaN-on-silicon platform. Optical modes propagate within the freestanding GaN membrane and their number decreases as the thickness of GaN membrane is reduced. Backside thinning of freestanding GaN membranes is used to obtain thinner GaN membranes that are helpful to reduce resonance modes and to broaden the reflectance interference fringes in the visible range. Strong coupling between the incident light and the circular grating is confirmed by angular-resolved reflectance measurement. The influences of the grating parameters on the reflectance spectra are investigated. This letter opens the way to fabricate single-layer GaN resonant gratings in the visible wavelength range.

Suspended membrane GaN gratings for refractive index sensing

In this paper, we describe the fabrication and the novel procedure for back thinning the GaN layer, which leads to improved optical performance. Angular-resolved reflectance measurements are then conducted to characterize the GaN gratings and show the dependence of resonant wavelength on grating period and membrane thickness. The measured results compare well with electromagnetic modeling based on rigorous coupled wave analysis (RCWA). Altering the dielectric environment has been shown as a novel sensing mechanism, and this work opens the way to the fabrication of novel GaN resonant photonic devices for refractive index sensing applications in the visible wavelength range.

Surface-normal emission from subwavelength GaN membrane grating

We present here the fabrication of subwavelength GaN membrane grating with a double-side process. Controllable GaN membrane thickness is achieved by backside thinning technique, which is essential to realize guided-mode resonant GaN grating in the visible range. Subwavelength GaN grating can serve as an optical resonator and accommodate surface-normal emission coupling. The measured photoluminescence (PL) spectra are sensitive to the parameters and shapes of GaN gratings. Both numerical simulation and reflectivity measurement are in consistent with the PL experimental results. This work opens a promising way to embed GaN-based photon emitter inside subwavelength grating to further produce a surface emitting device with a single layer GaN grating.

Polarization dependent light extraction of a GaN light emitting diode using dark field angle-resolved photoluminescence spectrometry

In this paper, the polarization dependent optical properties of GaN surface relief grating are investigated using dark field angle-resolved photoluminescence (ARPL) spectrometer. The light extraction efficiency with the transverse electric (TE) and transverse magnetic (TM) pumping source represents a TE polarized dominated property. It is found that the TE and TM waveguide modes cannot be simultaneously coupled out, therefore light extraction is polarization dependent. The ARPL spectrum also reveals that the extraction efficiency is relatively high as the dispersion line of the waveguide mode is coincident with the folded free-photon dispersion of the 1D GaN grating.

Patterned growth of InGaN/GaN quantum wells on freestanding GaN grating by molecular beam epitaxy

We report here the epitaxial growth of InGaN/GaN quantum wells on freestanding GaN gratings by molecular beam epitaxy (MBE). Various GaN gratings are defined by electron beam lithography and realized on GaN-on-silicon substrate by fast atom beam etching. Silicon substrate beneath GaN grating region is removed from the backside to form freestanding GaN gratings, and the patterned growth is subsequently performed on the prepared GaN template by MBE. The selective growth takes place with the assistance of nanoscale GaN gratings and depends on the grating period P and the grating width W. Importantly, coalescences between two side facets are realized to generate epitaxial gratings with triangular section. Thin epitaxial gratings produce the promising photoluminescence performance. This work provides a feasible way for further GaN-based integrated optics devices by a combination of GaN micromachining and epitaxial growth on a GaN-on-silicon substrate.PACS81.05.Ea; 81.65.Cf; 81.15.Hi.

Freestanding circular GaN grating fabricated by fast-atom beam etching

We report here a top-down process for fabricating a freestanding circular GaN grating. The circular gratings are defined by electron-beam lithography and realized by fast-atom beam (FAB) etching. The silicon substrate below the GaN grating region is completely removed to make the circular grating suspended in space. The optical responses of the fabricated GaN gratings are characterized in reflectance measurements. The polarization-independent responses of circular gratings are experimentally demonstrated, corresponding well with the theoretical prediction. This work represents an important step in combining GaN-based material with freestanding nanostructures.

Gratings in GaN Membranes

In this work, gratings are fabricated on the GaN thin film grown on the silicon substrates. GaN membranes are obtained by removing the silicon below the GaN gratings. The samples are stacked on the GaN diffractive microlenses on sapphire substrates fabricated using gray-level masks. The stacked components are characterized using a He-Ne laser. The laser beam is collimated by the GaN microlenses and diffracted by the GaN gratings. The result demonstrates a stacked microoptics systems in GaN-based materials for the first time.

Development of GaN and InGaN Gratings by Dry Etching

ABSTRACTSub-micron periodic gratings with pitch ∼3,000Å were formed in GaN and InGaN using holographic lithography and room temperature ECR BCl3/N2 dry etching at moderate microwave (500W) and rf (100W) powers. The process produces uniform gratings without the need for elevated sample temperatures during the etch step.