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.
We proposed a new type of the methanol concentration sensor that may be integrated directly to the GaP nanostructured photocathode. Necessary attribute for this design is the possibility to make it compatible with p-type of semiconductor. This condition follows from the fact that photocathodes for the CO2 splitting are exclusively prepared from p-type of semiconductors. Design of methanol sensor emanates from this principle. On the GaP substrate is deposited thin Pt supporting layer (100-200 nm thick).This layer is covered by 500 nm thick Nafion membrane that serves as proton filter. On the top of Nafion layer is deposited top Pt contact layer covered by thin nanostructured Pt layer layer with various thickness (0.5 -5 nm). This nanostructured Pt is formed into small islands. It serves as an absorption layer for methanol. Sensor detection properties were estimated from monitoring of I-V characteristics. They were measured in dark and under various methanol concentrations. Dark current values are in order 10-9 A, and this current increases up to order of microamps for methanol of concentration more than 95%.These measurements proved high sensitivity of the GaP compatible sensor structure. Methanol sensors were realized in form of narrow stripe on the side of the photocathode.
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.
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.
Proc. SPIE. 9441, 19th Polish-Slovak-Czech Optical Conference on Wave and Quantum Aspects of Contemporary Optics
KEYWORDS: Semiconductors, Gold, Lithography, Electron beam lithography, Light emitting diodes, Optical lithography, Photoresist materials, Near field scanning optical microscopy, Near field, Near field optics
We demonstrate capabilities of near-field scanning optical microscopy (NSOM) in collection and illumination mode. NSOM in collection mode was used for high resolution characterization of optical field of patterned light emitting diodes. In the scanned near field, we resolved enhanced emission from patterned regions with high resolution images of emitting surface. Also NSOM in illumination mode was used for patterning of predefined structures on semiconductor surfaces. For the diode patterning the electron beam direct writing lithography was used. Using NSOM lithography we prepared predefined planar structures in GaP surface. In the small open areas of predefined surface structure GaP nanowires were grown.
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.
Proc. SPIE. 8816, Nanoengineering: Fabrication, Properties, Optics, and Devices X
KEYWORDS: Lithography, Optical microscopes, Light emitting diodes, Optical lithography, Photoresist materials, Near field scanning optical microscopy, Optoelectronic devices, Near field, Photonics, Near field optics
Implementation of planar surface structures allows enhancement of light extraction from the light emitting diode (LED) surface due to diffraction-on-roughness based effect and photonic-band gap effect. Application of such structures can be attractive for overall and local enhancement of light from patterned areas of the LED surface. We used interference and near-field scanning optical microscope lithography for patterning of the surface of GaAs/AlGaAs based LEDs emitted at 840 nm. Also new approach with patterned polydimethylsiloxane (PDMS) membrane applied directly in the LED surface was investigated. Technology of patterned PDMS membranes using interference lithography and imprinting process was developed. The overall emission properties of prepared LED with patterned structure show enhanced light extraction efficiency, what was documented from near- and far-field measurements.
Nanowires (NW) exhibit unique electrical and optical properties due to lowered dimensions and related confinement effects. An integration of these tiny objects necessitates better understanding of their individual intrinsic properties. Precise electrical characterization of NWs requests preparation of electrical nanocontacts with high stability, low contact resistance and ohmic behaviour. We applied a conventional field-effect transistor configuration that allows to estimate a type of conductivity and carrier mobility also. Structural properties of individual NWs were studied by means of SEM and TEM techniques. The GaP nanowires under study were grown on the p-type GaP (111)B substrate by a VLS technique using 30 nm colloidal gold particles as seeds. A part of NWs was covered by a thin ZnO layer (10 – 140 nm) deposited by RF sputtering. Deposition of thin ZnO layer on the GaP nanowire led to creation of radial PN junction in core-shell configuration.
In this paper, effect of two-dimensional photonic pattern on the properties of the GaAs/AlGaAs based light emitting
diode (LED) is demonstrated. The interference lithography was employed to surface patterning of the GaAs/AlGaAs
based LED. The active region of the LED includes a GaAs/AlGaAs triple quantum well emitting at 850 nm. Interference
lithography was used for preparation of two-dimensional pattern in the upper diode layer. The prepared LED with two-dimensional
patterned photonic crystal structure was then investigated by electrical and optical measurements. Prepared
photonic crystal LED shows enhanced light extraction efficiency due to the more effective extraction of guiding modes,
what was documented from finite difference time domain simulations as well as from L(I) measurements.