HERZÁNOVÁ, K. Material Characterization and Modeling of Interband Cascade Light Emitting Diodes [online]. Brno: Vysoké učení technické v Brně. Fakulta strojního inženýrství. 2024.

Posudek vedoucího

Detz, Hermann

Mrs. Kristina Herzanova worked towards an improved the device model and associated material parameter set for interband cascade light emitting diodes. Her work combines experimental and computational methods to characterize unconventional materials and use the data for the verification of a state-of-the-art device model. The topic is highly relevant, as interband cascade light emitting diodes are in a state of very intense research and evolve to be compact and affortable broadband sources for mid-infrared spectroscopy. Her contributions to include spontaneous emission into a device model that was originally developed for lasers will without doubt remain a valuable part that originates form this thesis work. The thesis will impact future developments in the fields of optoelectronic devices and applications like mid-infrared bio-chemical or enviornmental spectroscopy. The thesis provides a general introduction to the field of mid-infrared optoelectronics and interband cascade devices in particular. Mrs. Herzanova then discusses the most relevant loss mechanisms that influence the device behavior. These sections form the basis for chapter four, which introduces the different experimental methods, summarizes results, obtained within the scope of this work and outlines the improved device model. This work clearly overachieved the objectives and therefore qualifies Mrs. Herzanova to receive a MSc degree in Physical Engineering and Nanotechnology from Brno University of Technology.

Posudek oponenta

Bastard, Gérald

Assessment of the Master thesis “Material characterization and modeling of interband cascade light emitting diodes” by Bc Kristina Herzanova The major part of this Master thesis addresses the different loss mechanisms present in the interband cascade devices; how the losses influence the device performance and what are the experimental methods used for the measurement and analysis of these losses. After recalling the main characteristics of the interband cascade lasers (ICL’s), notably the MBE growth of multi-layers of InAs/GaSb/AlSb), the author summarizes the main features of interband cascade light emitting devices (ICLED’s). This includes the material requested for the interband cascading, the design of basic heterostructures to achieve light emission and the examination of the various losses. This includes Shockley-Reed recombination on defects, Auger recombination, inter-valence and inter conduction absorption and free carrier absorption. Giving a few numbers for these mechanisms would have been useful and illustrative The author then describes the techniques of ellipsometry (measurements performed in Brno) and FTIR measurements (performed in Vienna) that she has used to extract the optical parameters and transmittance of different structural components of the interband cascade devices. These measurements are essential in choosing the suitable materials for the fabrication of ICLEDs. I find fig.(4.7) particularly illustrative as it shows a good agreement between the absorbance data from FTIR measurement and the imaginary part of the refractive index from ellipsometry measurement plotted against the wavenumber for the sample ICL1. This gives credence to the magnitude of the measured losses. The author has spent lots of efforts to ascertain the origin and magnitude of the losses in ICL’s. A particular attention was paid to valence intersubband absorption, which significantly degrades the performance of interband cascade devices in the mid-infrared region (l > 4 m). The measurements are summarized in fig.(4.12). I would have liked reading some elaboration on the reasons of the increases of the two curves: while losses increasing linearly with the current seem expectable, the threshold -like behavior of the losses versus V is not so straightforward. Experimental characterization of ICL waveguides revealed the impact of this absorption under various operating conditions, providing valuable insights for further device optimization. In summary, this thesis shows that several experimental techniques have been successfully used by the author, that she has a good command of the modelling required to analyze elaborate experimental data. Therefore, I heartfully recommend that Bc Kristina Herzanova receives a Master degree from the Brno University of Technology. June 4 2024 Gerald Bastard

eVSKP id 160586