IEM Distinguished Lecturers Seminar : What is special about ScxAl1‐xN ?
Event details
| Date | 03.06.2022 |
| Hour | 13:15 › 14:00 |
| Speaker |
Prof. Oliver Ambacher INATECH, University of Freiburg, Germany |
| Location | Online |
| Category | Conferences - Seminars |
| Event Language | English |
Abstract
Alloying Aluminum-Nitride (AlN) with the rare-earth metal Scandium (Sc) to form high quality crystalline thin films of wide bandgap semiconductors with hexagonal crystal structure has drawn tremendous attention due to the significantly enhanced piezoelectric response, the high pyroelectric polarization and the unique ferroelectric behavior, possible. The high piezoelectric, pyroelectric and ferroelectric polarizations in hexagonal ScxAl1-xN-crystals enriches the dimension of polarization engineering in group-III-nitride based heterostructures and provide opportunities for the integration of novel functionalities into electronic and optoelectronic 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 with interfaces free of polarization sheet charges, with benefit to light emitting devices, because of the missing Stark-effect or to design heterostructures with high positive as well as negative polarization induced interface charges in order to optimize electron and hole distribution profiles to the need of electronic devices. Electron charges and distribution profiles 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 polarization induced sheet charges, we use Dryer´s modern theory of polarization, which allows to consider the spontaneous polarization measured on ferroelectric ScxAl1-xN-layers. Because the sheet density of the electrons accumulating at the heterostructure interfaces can strongly depend on both the 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 the wurtzite to the hexagonal layered crystal structure occurs, we have calculated the carrier sheet densities and profiles for three representative datasets and evaluated their relevance for devices. We predict electron sheet densities of 2.26±0.201014 cm-2
and 6.25±0.201014 cm-2 
from all three sets of data for Ni/AlN/InN- and Ni/ScN/InN-heterostructures, respectively. 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 interface. We identify Ni/ScxAl1-xN/GaN-heterostructures with 0.13≤x≤0.19 
as particularly promising candidates for the processing of energy-efficient high electron mobility transistors due to their missing or low mechanical strain 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
, which point to electron accumulations of up to 8.02±0.401014 cm-2
. These heterostructures are not suitable for transistor devices, but they might be of great interest for the realization of low impedance contacts.
Bio
Oliver Ambacher received his diploma and doctor of natural sciences at the Ludwig‐Maximilians and the Technical University of Munich with distinction in 1989 and 1993. In 1993 he got a position as a research assistant at the Walter Schottky Institute at the Technical University of Munich, where he dealt with the growth of gallium nitride and its alloys with the help of molecular beam epitaxy and chemical vapor deposition. In 1995 he focused the research work of his group on the processing of GaN‐based electronic and optical components. He was significantly involved in the implementation of the first UV detectors, surface acoustic wave components, microwave amplifiers and sensors as well as in the research of polarization‐induced effects in GaN‐based hetero‐ and quantum structures. In 1998/99 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 his 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 director of the Institute for Solid State Electronics and two years later he was appointed director of the Center for Micro and Nanotechnologies. Since October 2007, Oliver Ambacher has been a professor at the Albert Ludwigs University in Freiburg and head of the Fraunhofer Institute for Applied Solid State Physics. In 2015 he received the Karl Heinz Beckurts Prize for his contributions to the development of highly efficient power amplifiers based on GaN for the latest generation of mobile phone base stations. In 2021 he was awarded the Rudolph Jäckel Prize for the development of energy‐efficient power electronics.
Alloying Aluminum-Nitride (AlN) with the rare-earth metal Scandium (Sc) to form high quality crystalline thin films of wide bandgap semiconductors with hexagonal crystal structure has drawn tremendous attention due to the significantly enhanced piezoelectric response, the high pyroelectric polarization and the unique ferroelectric behavior, possible. The high piezoelectric, pyroelectric and ferroelectric polarizations in hexagonal ScxAl1-xN-crystals enriches the dimension of polarization engineering in group-III-nitride based heterostructures and provide opportunities for the integration of novel functionalities into electronic and optoelectronic 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 with interfaces free of polarization sheet charges, with benefit to light emitting devices, because of the missing Stark-effect or to design heterostructures with high positive as well as negative polarization induced interface charges in order to optimize electron and hole distribution profiles to the need of electronic devices. Electron charges and distribution profiles 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 polarization induced sheet charges, we use Dryer´s modern theory of polarization, which allows to consider the spontaneous polarization measured on ferroelectric ScxAl1-xN-layers. Because the sheet density of the electrons accumulating at the heterostructure interfaces can strongly depend on both the 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 the wurtzite to the hexagonal layered crystal structure occurs, we have calculated the carrier sheet densities and profiles for three representative datasets and evaluated their relevance for devices. We predict electron sheet densities of 2.26±0.201014 cm-2
and 6.25±0.201014 cm-2 
from all three sets of data for Ni/AlN/InN- and Ni/ScN/InN-heterostructures, respectively. 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 interface. We identify Ni/ScxAl1-xN/GaN-heterostructures with 0.13≤x≤0.19 
as particularly promising candidates for the processing of energy-efficient high electron mobility transistors due to their missing or low mechanical strain 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
, which point to electron accumulations of up to 8.02±0.401014 cm-2
. These heterostructures are not suitable for transistor devices, but they might be of great interest for the realization of low impedance contacts.Bio
Oliver Ambacher received his diploma and doctor of natural sciences at the Ludwig‐Maximilians and the Technical University of Munich with distinction in 1989 and 1993. In 1993 he got a position as a research assistant at the Walter Schottky Institute at the Technical University of Munich, where he dealt with the growth of gallium nitride and its alloys with the help of molecular beam epitaxy and chemical vapor deposition. In 1995 he focused the research work of his group on the processing of GaN‐based electronic and optical components. He was significantly involved in the implementation of the first UV detectors, surface acoustic wave components, microwave amplifiers and sensors as well as in the research of polarization‐induced effects in GaN‐based hetero‐ and quantum structures. In 1998/99 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 his 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 director of the Institute for Solid State Electronics and two years later he was appointed director of the Center for Micro and Nanotechnologies. Since October 2007, Oliver Ambacher has been a professor at the Albert Ludwigs University in Freiburg and head of the Fraunhofer Institute for Applied Solid State Physics. In 2015 he received the Karl Heinz Beckurts Prize for his contributions to the development of highly efficient power amplifiers based on GaN for the latest generation of mobile phone base stations. In 2021 he was awarded the Rudolph Jäckel Prize for the development of energy‐efficient power electronics.
Practical information
- General public
- Free
Organizer
- Institute of Electrical and Micro Engineering (IEM)
Contact
- Prof. Elison Matioli, IEM
Prof. Romain Fleury, IEM