A. Laurenčíková

Modification of LED radiation pattern by implementation of 1D Fresnel structure in the surface

In this contribution, we present modification of far field of light emitting diode (LED) with implemented Fresnel structure in the LED surface. Fresnel structures were prepared in one-dimensional arrangement with two different foci f1 = 12.5 μm and f2 = 1 cm. Structures were etched directly in the LED emitting surface using electron beam lithography with the etched depth for the structure with f1 and f2 app. 200 nm and 400 nm, respectively. Due to application of these structures, LED far field narrowing was observed, which is documented by goniophotometer measurements. For the structure with f1 and f2, the intensity decrease for angles ±30° – ±50° is app. 3-4% and 5-6%, respectively, in comparison to the Lambertian profile.

Reflectance measurements of GaP-ZnO core-shell NWs

This paper reports on optical measurements of GaP nanowire (NW) arrays with thin nanocrystalline ZnO layer. The GaP core was prepared by metal organic vapor phase epitaxy (MOVPE) and the ZnO shell by RF sputtering by different sputtering conditions. The NWs were grown from Au seeds created from very thin Au layer deposited on top of GaP substrate. Reflectance of different NWs structures covered by ZnO coating was measured in angular dependence in wide range of angles and compared. We experimentally show the reflectance suppression of the ZnO coated NWs in the wide range of angles.

Optical properties of GaAs-based LED with Fresnel structure in the surface

This contribution presents implementation of one dimensional Fresnel structure in surface emitting part of the AlGaAs/GaAs multi-quantum well light emitting diode (LED).The structure consists in drilled lines distributed with square root of distance in order to obtain structures with different foci. First structure was prepared by electron beam lithography and etched directly in the emitting surface using reactive-ion etching. Second structure was prepared in the surface of thin PDMS membrane that can be stack directly on the emitting surface. The membrane is fabricated using dip in laser lithography combined with PDMS embossing. Implementation of such Fresnel structures leads in modification of LED far-field what was proved by goniophotometer measurements.

Predefined planar structures in semiconductor surfaces patterned by NSOM lithography

Near-field scanning optical microscope (NSOM) lithography is one of optical technologies for planar structure fabrication, where exposure process is performed by optical near field produced at tip of fiber probe. Maskless exposure of defined regions is performed so that different periodic and predefined arrangement can be achieved. In this contribution, NSOM lithography is presented as effective tool for semiconductor device surface patterning. Non-contact mode of NSOM lithography was used to pattern planar predefined structures in GaAs, AlGaAs and GaP surfaces. In this way, GaAs/AlGaAs-based LED with patterned structure in the emitting surface was prepared, where patterned air holes show enhancement of radiation in comparison with the surrounding surface. Furthermore, NSOM in combination with lift-off technique was used to prepare metal-catalyst particles on GaP substrate for subsequent growth of GaP nanowires which can be used in photovoltaic applications.