Jaroslava Škriniarová

Periodic structures prepared by two-beam interference method

We present an optical interference method as the efficient tool for high-quality one- (1D) and two-dimensional (2D) periodic structure fabrication. Different types of 2D periodic structures are prepared using two-beam interference technique by double exposure. Also, the patterning of Au layer is provided using two-beam interference method. Quite homogeneous 1D and 2D structures with small periodicity were prepared in photoresist and Au layer. The experimentally prepared structures are well in agreement with the theoretically designed ones. According to experimental results, we favor two-beam interference technique using multi-exposure process as a very useful method for fabrication of 2D periodic structures and devices for integrated optoelectronics.

Electrical Properties of Recessed Algan/Gan Schottky Diodes Under off–State Stress

Abstract Electrical properties of recessed and non-recessed AlGaN/GaN Schottky diodes under off-state stress were investigated. The samples were consecutively stressed by the stepped negative bias (−60 V). Before and after the stress I−V and C−V characteristics were evaluated to verify the device degradation process. Finally, the degradation mechanism and the influence of AlGaN recessed layer thickness on the electrical properties of the Schottky diodes were analysed. It was found that the short time stress influence on I−V characteristics was most negligible for the non-recessed sample. Shallow and deep recessed samples exhibited initial trap filling and reverse current decrease. Generally it was found that the stress voltage near 60 V caused recoverable device degradation

Structures patterning by non-contact NSOM lithography

This contribution presents experimental results from the fabrication of planar photonic structures with two-dimensional (2D) arrangement. We demonstrate the near-field scanning optical microscope (NSOM) lithography as an effective optical method for fabrication of 2D photonic structures in thin photoresist layer. We employ a non-contact mode of NSOM lithography using a metal coated fiber tip in combination with 3D nanoposition piezosystem. Prepared photonic structures in thin photoresist layer deposited on the GaAs substrate are analyzed by scanning probe diagnostics. Set of experiments was realized in order to improve the aspect ratio of the patterned structures, where the exposure time and the intensity of the exposing field were parameters.

The AZ 5214E Resist in EBDW Lithography and its Use as a RIE Etch–Mask in Etching Thin Ag Layers in N2 Plasma

Abstract In this article we describe the electron-beam direct-write (EBDW) lithography process for the AZ 5214E photoresist which is, besides its sensitivity to UV radiation, sensitive also to electrons. An adapted process flow is provided. At the same time we examine the resistance of this resist to RIE and its suitability as an etch-mask for etching thin Ag layers in N2 plasma. A comparison with several chosen resists (PMMA, ma-2405, ma-N 1402, SU-8 2000) is provided.

Advanced optical methods for patterning of photonic structures in photoresist, III-V semiconductors and PMMA

This contribution presents experimental results in the field of planar two-dimensional (2D) photonic crystal (PhC) structures, as well as their design, fabrication and analysis. We demonstrate maskless optical methods leading to fabrication of 2D PhC structures for applications in optoelectronics. The 2D PhC structures of square and triangular symmetries with period from 275 nm to 2 μm were fabricated in thin photoresist layer, III-V semiconductor surfaces and polymethylmethacrylate using interference lithography and near-field scanning optical microscope lithography. The 2D PhC structures prepared in GaAs surface were used as a mold for nanoimprint lithography in polymethylmethacrylate.

Electrical property dependence on thickness and morphology of nanocrystalline diamond thin films

In this study, we investigate the influence of nanocrystalline diamond (NCD) thin film morphology and thickness on their electrical properties. NCD films are grown on p-type Si substrates with varied thicknesses from 250 to 788nm. Electrical contacts are formed from combination of Ti/Au metal layers (100nm thick each). The I-V and breakdown field measurements are used to analyze the electrical properties of metal/NCD/Si sandwich structure. In addition, NCD films are analyzed by scanning electron microscopy and Raman spectroscopy for better interpretation of the I-V measurements.

Optical and electrical characterization of photonic crystal light emitting diodes

The paper deals with electrical and optical characterization of the Al0.295Ga0.705As/GaAs multi-quantum well light emitting diode (MQW LED) structure including two-dimensional photonic crystals (2D PhC) patterned in the LED surface. The active region of LED consists of three quantum wells with emitting maximum at 845 nm. The effect of photonic crystal with square symmetry and 500 nm grating period on electrical and optical properties of LED was investigated. The measurements of L-I characteristics show, that app. 3 times higher optical power from LED structure was achieved using photonic crystals in comparison with structure without PhC.

Light emitting diode with 2D PhC structure in the surface analysed by NSOM

We present light emitting diode with two-dimensional photonic crystal structure prepared by interference lithography in the light emitting diode surface with an emission maximum at 845 nm. Applied two-dimensional photonic crystal structure improved light extraction efficiency for more than 30 %. The photonic crystal light emitting diode surface morphology was analyzed by atomic force microscope. The enhanced extraction efficiency of the photonic crystal diode was documented from L(I) dependencies from the near-field studies.

Characterisation of electrical properties of AlGaN/GaN Schottky diode at very high temperature

Recent progress in GaN based high electron mobility transistors (HEMTs) has revealed them to be strong candidates for future high power devices at high frequency operation. In order to extract and utilize the favorable GaN material properties, however, there are still a lot of areas to be investigated. Among them the most important is to develop new processes, structure design and characterization techniques. Determination of the effective Schottky barrier height φb on GaN and related compound semiconductors with higher precision is important for further analysis of new combinations of metals and semiconductors and better understanding of physical behaviour at the interface. In this paper we present the modified method of evaluation of the selected parameters on the AlGaN/GaN heterostructure from the I–V measurement in a wide temperature range.

Preparation and properties of Zn delta-doped GaAs/AlGaAs heterojunction phototransistor

We have prepared, characterized and discussed the performance of AlGaAs/GaAs heterojunction bipolar phototransistor (HPT) including Zn delta-doped base. Due to the existence of Δ-doped sheets located in the middle of undoped GaAs base the Δ-doped HPT devices exhibit low dark current, nearly zero offset voltage, saturation voltage ~0.4V, and rise and fall times in ns range at wavelength of 850nm up to 6V of applied voltage. Due to avalanche multiplication behavior at the collector junction, an increased optical gain G>10 can be reached for applied voltages in the range of 6-12V. For voltages higher than the device breakdown voltage (~12V) switching and negative differential resistance (NDR) effect is measurable in the inverted mode of operation.