BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Memento EPFL// BEGIN:VEVENT SUMMARY:IEM Distinguished Lecturers Seminar : What is special about ScxAl1 ‐xN ? DTSTART:20220603T131500 DTEND:20220603T140000 DTSTAMP:20260924T085511Z UID:905b40f5a1d6a1efbb76145244bb95ac258ede042133b91f517a338e CATEGORIES:Conferences - Seminars DESCRIPTION:Prof. Oliver Ambacher\nINATECH\, University of Freiburg\, Germ any\nAbstract\nAlloying Aluminum-Nitride (AlN) with the rare-earth metal S candium (Sc) to form high quality crystalline thin films of wide bandgap s emiconductors with hexagonal crystal structure has drawn tremendous attent ion due to the significantly enhanced piezoelectric response\, the high p yroelectric polarization and the unique ferroelectric behavior\, possible. The high piezoelectric\, pyroelectric and ferroelectric polarizations in hexagonal ScxAl1-xN-crystals enriches the dimension of polarization engine ering in group-III-nitride based heterostructures and provide opportunitie s for the integration of novel functionalities into electronic and optoele ctronic devices. The possibility\, that hexagonal ScxAl1-xN-layers can be grown biaxial compressive as well as tensile biaxial strained on GaN- and InN-buffer layers\, creates the opportunity to engineer heterostructures w ith interfaces free of polarization sheet charges\, with benefit to light emitting devices\, because of the missing Stark-effect or to design hetero structures with high positive as well as negative polarization induced int erface charges in order to optimize electron and hole distribution profile s to the need of electronic devices. Electron charges and distribution pro files induced by gradients in polarization at interfaces of pseudomorphic\ , hexagonal ScxAl1-xN/GaN- and ScxAl1-xN/InN-heterostuctures are simulated by Schödinger-Poisson solver and presented for the whole range of random ScxAl1-xN-alloys\, considering the transition from wurtzite to hexagonal layered crystal structure. In contrast to previous calculations of polariz ation induced sheet charges\, we use Dryer´s modern theory of polarizatio n\, which allows to consider the spontaneous polarization measured on ferr oelectric ScxAl1-xN-layers. Because the sheet density of the electrons acc umulating at the heterostructure interfaces can strongly depend on both th e data set of the piezoelectric and structural coefficients as well as on the alloying region of the ScxAl1-xN-layers in which the transition from t he wurtzite to the hexagonal layered crystal structure occurs\, we have ca lculated the carrier sheet densities and profiles for three representative datasets and evaluated their relevance for devices. We predict electron s heet densities of 2.26±0.201014 cm-2 and 6.25±0.201014 cm-2 from all th ree sets of data for Ni/AlN/InN- and Ni/ScN/InN-heterostructures\, respect ively. We demonstrate\, that the polarization induced interface charges of Ni/ScxAl1-xN/InN-heterostructures are always positive\, tend to increase with increasing Sc-content and can cause electron accumulations which lead to flooding of the triangular quantum wells at the semiconductor interfac e. We identify Ni/ScxAl1-xN/GaN-heterostructures with 0.13≤x≤0.19 as p articularly promising candidates for the processing of energy-efficient hi gh electron mobility transistors due to their missing or low mechanical st rain and their large electron sheet densities between 4.11±0.201013 cm-2  and 6.37±0.201013 cm-2. Furthermore\, we present simulation results of highly strained Ni/ScxAl1-xN/GaN-heterostructures for 0.81≤x≤1.0\, whi ch point to electron accumulations of up to 8.02±0.401014 cm-2. These het erostructures are not suitable for transistor devices\, but they might be of great interest for the realization of low impedance contacts.\n\n\nBio\ nOliver Ambacher received his diploma and doctor of natural sciences at th e Ludwig‐Maximilians and the Technical University of Munich with distinc tion in 1989 and 1993. In 1993 he got a position as a research assistant a t the Walter Schottky Institute at the Technical University of Munich\, wh ere he dealt with the growth of gallium nitride and its alloys with the he lp of molecular beam epitaxy and chemical vapor deposition. In 1995 he foc used the research work of his group on the processing of GaN‐based elect ronic and optical components. He was significantly involved in the impleme ntation of the first UV detectors\, surface acoustic wave components\, mic rowave amplifiers and sensors as well as in the research of polarization ‐induced effects in GaN‐based hetero‐ and quantum structures. In 199 8/99 he was offered the Feodor Lynen grant from the Alexander von Humboldt Foundation at Cornell University (USA) to deepen his work in the field of AlGaN/GaN transistors for high‐frequency power amplifiers. Following hi s habilitation in experimental physics in 2000 and his promotion to senior assistant in 2001\, he was appointed professor for nanotechnology at the Technical University of Ilmenau a year later. In 2002 he was elected direc tor of the Institute for Solid State Electronics and two years later he wa s appointed director of the Center for Micro and Nanotechnologies. Since O ctober 2007\, Oliver Ambacher has been a professor at the Albert Ludwigs U niversity in Freiburg and head of the Fraunhofer Institute for Applied Sol id State Physics. In 2015 he received the Karl Heinz Beckurts Prize for hi s contributions to the development of highly efficient power amplifiers ba sed on GaN for the latest generation of mobile phone base stations. In 202 1 he was awarded the Rudolph Jäckel Prize for the development of energy ‐efficient power electronics. LOCATION:ELA 1 https://plan.epfl.ch/?room==ELA%201 https://epfl.zoom.us/j/ 69331525319 STATUS:CONFIRMED END:VEVENT END:VCALENDAR