Master thesis: Temperature-dependent structural characterization of scandium aluminum nitride (ScAlN).

Master Topic:

To reduce the energy consumption of electrical devices, both transistors and MEMS in general need to be more energy efficient. The ternary semiconductor material ScAlN is currently of particular interest due to its excellent piezoelectric and ferroelectric properties. At high scandium concentrations, this material undergoes a phase transition from hexagonal wurtzite structure to cubic rock salt structure. Exactly under what growth conditions and at what scandium concentration this occurs is still under investigation. Heat is generated during the operation of power electronic devices, causing the materials to expand. The heterostructures of transistors consist of various compound semiconductors such as AlN, GaN, ScN and their ternary alloys. The thermal expansion coefficients of these materials differ, which can lead to stresses or even cracks within the layer. The coefficient of thermal expansion for the novel, cubic ScAlN has not been experimentally determined at this time. The volume change of the material is measured by X-ray diffraction (XRD) using in-situ measurements at high temperatures. This allows the coefficient of thermal expansion α to be determined. By an improved sputtering epitaxy method of our cooperation partners, state-of-the-art ScAlN heterostructures can be provided.

Details:

• Usual duration: 6 months
• Start: immediately
• Prior Knowledge:
• Fundamentals in solid state and semiconductor physics as well as crystallography are helpful
• Studies in Sustainable Systems Engineering, Microsystems Engineering, Physics, Chemistry, Materials Science, or a comparable scientific-technical subject
• In addition to the master thesis, a HiWi position can be offered to support the scientific projects of the chair up to max. 40h/month

Activity Description:

• Introduction to the fundamentals of X-ray structural analysis of semiconductor nitrides

• Determination of lattice parameters and other structural properties at temperatures up to 900 °C by X-ray diffraction (XRD)

• Determination of the thermal expansion coefficient α of cubic ScAlN thin films

• Calculation of the stresses within the layer at elevated temperatures

• Improvement of the fitting parameters of the Debye model to the measured data

We expect:

• Interest in the characterization of novel materials
• Pleasure in participating in a team of researchers

We offer:

• Introduction to the topic and the measurement methodology as a student assistant

• Learning to operate an X-ray diffractometer independently in combination with a heating dome, which allows measurements at elevated temperatures

• Thorough introduction to the state of the art of research on III-V semiconductors and a workstation at INATECH

• Training in further characterization techniques such as atomic force microscopy (AFM), electrical measurements (CV, IV), ...

Contact

Prof. Dr. Dr. Oliver Ambacher

INATECH - Leistungselektronik
Emmy-Noether-Straße 2
79110 Freiburg im Breisgau

oliver.ambacher@inatech.uni-freiburg.de