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Warsaw, Poland

Piotrzkowski R.,Polish Academy of Sciences | Litwin-Staszewska E.,Polish Academy of Sciences | Grzanka S.,Polish Academy of Sciences | Grzanka S.,TopGaN Ltd.
Applied Physics Letters | Year: 2011

Modern optoelectronic devices are often based on wide-bandgap semiconductors such as GaN. In such cases the current injecting contacts are usually nonlinear, especially for p-type materials. Using the standard transmission line method (TLM), which gives satisfactory results in linear cases, characterization of nonlinear contacts can lead to serious ambiguities. In this Letter, we derive exact formulas permitting to extract the current-voltage characteristics of the non-linear metal-semiconductor contact from measurements performed on standard TLM pattern, as well as to simulate behavior of such pattern for given model contact characteristic. The application of this generalized TLM method is illustrated on the example of Ni/Au contacts on p-GaN © 2011 American Institute of Physics. Source

Domagala J.Z.,Polish Academy of Sciences | Morelhao S.L.,University of Sao Paulo | Sarzynski M.,Polish Academy of Sciences | Mazdziarz M.,Polish Institute of Fundamental Technological Research | And 2 more authors.
Journal of Applied Crystallography | Year: 2016

Epitaxy of semiconductors is a process of tremendous importance in applied science and in the optoelectronics industry. The control of defects introduced during epitaxial growth is a key point in manufacturing devices of high efficiency and durability. In this work, it is demonstrated how useful hybrid reflections are for the study of epitaxial structures with anisotropic strain gradients due to patterned substrates. High accuracy in detecting and distinguishing elastic and plastic relaxations is one of the greatest advantages of measuring this type of reflection, as well as the fact that the method can be exploited in a symmetric reflection geometry on a commercial high-resolution diffractometer. © 2016 International Union of Crystallography. Source

Kamyczek P.,Wroclaw University of Technology | Placzek-Popko E.,Wroclaw University of Technology | Kolkovsky Vl.,TU Dresden | Grzanka S.,TopGaN Ltd. | And 3 more authors.
Journal of Applied Physics | Year: 2012

In the present study, the electrical and optical properties of deep defects in p-i-n GaN junction and AlGaN/GaN heterojunction are investigated by means of the deep level transient spectroscopy (DLTS), Laplace DLTS, and electroluminescence (EL) techniques. We demonstrate that in both structures the yellow luminescence (YL) is a dominant band in the EL spectra recorded at room temperature. We correlate the YL band with the minority DLTS peaks observed at about 370 K. A gallium vacancy-related defect seems to be a probable candidate as to the origin of the defect. Another dominant majority peak observed in the DLTS studies was concluded to be linked with a donor-like defect in the upper half of the bandgap. The origin of the defect is discussed. © 2012 American Institute of Physics. Source

Kudrawiec R.,Wroclaw University of Technology | Gladysiewicz M.,Wroclaw University of Technology | Janicki L.,Wroclaw University of Technology | Misiewicz J.,Wroclaw University of Technology | And 6 more authors.
Applied Physics Letters | Year: 2012

Contactless electroreflectance (CER) has been applied to study the Fermi-level position on c-plane GaN surface in Van Hoof structures grown by molecular beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOVPE). A clear CER resonance followed by strong Franz-Keldysh oscillation (FKO) of various periods was clearly observed for the series of samples of different thicknesses (30, 50, and 70 nm) of undoped GaN layer. The built-in electric field in this layer has been determined from the period of GaN-related FKO. A good agreement between the calculated and measured electric fields has been found for the Fermi-level located ∼0.4 and ∼0.3 eV below the conduction band for the MBE and MOVPE samples, respectively. © 2012 American Institute of Physics. Source

Kafar A.,Polish Academy of Sciences | Stanczyk S.,Polish Academy of Sciences | Targowski G.,TopGaN Ltd. | Oto T.,Kyoto University | And 5 more authors.
Applied Physics Express | Year: 2013

We demonstrate blue-violet InGaN superluminescent diodes (SLDs) with bent-waveguide (j-shape) geometry, emitting optical power exceeding 200mW for SLD with 1-mm-long waveguide. The adopted j-shape geometry prevents devices from lasing, even at the highest applied currents (450 mA). However, high-resolution measurements reveal the appearance of spectral ripples at currents on the order of 250 mA. The maximum output power increases with the waveguide length. © 2013 The Japan Society of Applied Physics. Source

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