A new type of nanostructured selective ultraviolet (UV) refl ecting mirror is presented. Periodic porous multilayers with photonic crystal properties are built by spin-coating-assisted layer-by-layer deposition of colloidal suspensions of nanoparticles of ZrO 2 and SiO 2 (electronic band gap at λ < 220 nm). These optical fi lters are designed to block well-defi ned wavelength ranges of the UVA, UVB, and UVC regions of the electromagnetic spectrum while preserving transparency in the visible. The shielding against those spectral regions arises exclusively from optical interference phenomena and depends only on the number of stacked layers and the refractive index contrast between them. In addition, it is shown that the accessible pore network of the as-deposited multilayer allows preparing thin, fl exible, self-standing, transferable, and adaptable selective UV fiby polymer infi ltration, without signifi cantly losing refl ectance intensity, i.e., preserving the dielectric contrast. These fi lms offer a degree of protection comparable to that of traditional ones, without any foreseeable unwanted secondary effects, such as photodegradation, increase of local temperature or, as is the case for organic absorbers, generation of free radicals, all of which are caused by light absorption.

https://digital.csic.es/bitstream/10261/121217/1/Smirnov_et_al-2013-Advanced_Functional_Materials.pdf

Selective UV Reflecting Mirrors Based on Nanoparticle Multilayers

To investigate the function of chlorination treatment, Schottky diodes with Ni∕Au contact and chlorine-treated n-type GaN were fabricated. The resultant Schottky barrier height and ideality factor of the chlorine-treated Schottky diodes were improved. The corresponding increase in photoluminescence intensity and carrier lifetime of the chlorine-treated n-type GaN was achieved using photoluminescence and time-resolved photoluminescence measurements. The improved performance of chlorine-treated Schottky diodes was attributed to the reduction of surface states as a result of reduced Ga dangling bonds and the N vacancies being passivated by the formation of GaOx on the surface of n-type GaN.

/pdf/schottky-mechanism-for-ni-au-contact-with-chlorine-treated-n-3okc1trk12.pdf

Schottky mechanism for Ni∕Au contact with chlorine-treated n-type GaN layer

Comparable microcavities with 3λ∕2 (∼240nm) active regions containing distributed (In,Ga)N quantum wells, grown on GaN substrates and bounded by two dielectric mirrors, have been fabricated by two different routes: one using laser lift-off to process structures grown on GaN-on-sapphire templates and the second using freestanding GaN substrates, which are initially processed by mechanical thinning. Both exploit the properties of an Al0.83In0.17N layer, lattice matched to the GaN substrate and spacer layers. In both cases cavity quality factors >400 are demonstrated by measurements of the cavity-filtered room-temperature excitonic emission near 410nm.

/pdf/in-ga-n-gan-microcavities-with-double-dielectric-mirrors-qhzmcvcqra.pdf

(In,Ga)N/GaN microcavities with double dielectric mirrors fabricated by selective removal of an (Al,In)N sacrificial layer

The processing of N-polar GaN (0001 ¯) samples has been studied, motivated by applications in which extensive back side thinning of freestanding GaN (FS-GaN) substrates is required. Experiments were conducted on FS-GaN from two commercial sources, in addition to epitaxial GaN with the N-face exposed by a laser lift-off process. The different types of samples produced equivalent results. Surface morphologies were examined over relatively large areas, using scanning electron microscopy and stylus profiling. The main focus of this study was on inductively coupled plasma (ICP) etch processes, employing Cl2∕Ar or Cl2∕BCl3Ar gas mixtures. Application of a standard etch recipe, optimized for feature etching of Ga-polar GaN (0001) surfaces, caused severe roughening of N-polar samples and confirmed the necessity for specific optimization of etch conditions for N-face material. A series of recipes with a reduced physical (sputter-based) contribution to etching allowed average surface roughness values to be consiste...

Thinning of N-face GaN (0001 ¯) samples by inductively coupled plasma etching and chemomechanical polishing

Two routes for the fabrication of bulk GaN microcavities embedded between two dielectric mirrors are described, and the optical properties of the microcavities thus obtained are compared. In both cases, the GaN active layer is grown by molecular beam epitaxy on (111) Si, allowing use of selective etching to remove the substrate. In the first case, a three period Al0.2Ga0.8N/AlN Bragg mirror followed by a λ/2 GaN cavity are grown directly on the Si. In the second case, a crack-free 2 μm thick GaN layer is grown, and progressively thinned to a final thickness of λ. Both devices work in the strong coupling regime at low temperature, as evidenced by angle-dependent reflectivity or transmission experiments. However, strong light-matter coupling in emission at room temperature is observed only for the second one. This is related to the poor optoelectronic quality of the active layer of the first device, due to its growth only 250 nm above the Si substrate and its related high defect density. The reflectivity sp...

/pdf/strong-light-matter-coupling-in-bulk-gan-microcavities-with-4prdvpivgh.pdf

Strong light-matter coupling in bulk GaN-microcavities with double dielectric mirrors fabricated by two different methods

GaN microcavity structure with SiO2∕ZrO2 dielectric distributed Bragg reflectors was fabricated by means of transferring an InGaN∕GaN multiple quantum well (QW) structure from the (111) Si substrate onto a sapphire carrier and wet-chemical etching of the substrate A dip in the reflectivity spectrum of the microcavity structure is observed at a wavelength of 411nm indicating the cavity resonance mode Also, the strong influence of the cavity on the QW photoluminescence has been observed A sharp emission spectrum, with a linewidth of 35nm, occurs at a wavelength of 411nm coincided with the position of the cavity resonance mode

GaN microcavity structure with dielectric distributed Bragg reflectors fabricated by using a wet-chemical etching of a (111) Si substrate

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GaN microcavity structure with dielectric distributed Bragg reflectors fabricated by using a wet-chemical etching of a (111) Si substrate