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Ferroelectric-Ga2O3 interface for power electronics

Contact: BARRETT Nick, , nick.barrett@cea.fr, +33 1 69 08 32 72
Summary:
The internship will be a preliminary study of the possibility to increase the range of Ga2O3 based devices using ferroelectric HfO2. It will studying the chemical and electronic structure of the interface using XPS and PEEM to image the ferroelectric domains.
Possibility of continuation in PhD: Oui
Deadline for application:27/03/2020

Full description:
Ferroelectric-Ga2O3 interface for power electronics
Ga2O3 belongs to the family of ultra wide band gap semiconductors with potentially unrivalled performance in power electronics thanks to breakdown fields EBD up to 8-12 MV/cm. The high band gap allows operation at high voltages and elevated temperatures, making Ga2O3 ideally suited for power electronics applications in hostile or demanding environments.
Unfortunately, Ga2O3 cannot be readily p-doped. As a result, it can only be used to make unipolar devices. The absence of p doping, due to the tendency of hole self-trapping [Varley2012] means that Ga2O3 based p-n junctions do not exist and MOSFETs in enhancement mode with possible power switch applications are not possible.
The internship will be a preliminary study of the possibility to increase the range of Ga2O3 based devices by introducing an additional functional layer to the device stack. Ferroelectricity provides such a functionality with two equivalent ground states of opposite macroscopic electric polarization, switchable under an applied field. Insertion of a thin FE layer, by definition highly insulating, between the Schottky electrode and the Ga2O3 layer in a SBD or between the gate and the channel in a power MOSFET would provide two conducting states.

In a SBD the FE layer would limit leakage current and the internal bias of the FE could tune the operating voltage, reducing power consumption for mobile devices. In Ga2O3 MOSFETs the insertion of a FE layer between the metal gate and the channel could shift the transistor operating mode to enhancement, i.e. at VGS = 0 the channel would become non-conducting.
The robust nature of the FE polarization and hence the additional internal voltage in the gate stack, could therefore extend the operating modes of both two and three terminal devices.
The internship will consist of studying the chemical and electronic structure of the interface between ferroelectric HfO2[Böschke2011] grown on doped Ga2O3 using X-photoemission spectroscopy (XPS) and photoemission electron microscopy (PEEM) to image the ferroelectric domains in HfO2 [Copie2017].
This work is part of an ongoing collaboration with the Air Force Reseach laboratory in Dayton, Ohio (USA) who will supply the samples.
[Varley2012] J.B. Varley et al., Physical Review B 85, 081109 (2012)
[Böschke2011] T. S. Böscke, J. Müller, D. Bräuhaus, U. Schröder, and U. Böttger, Applied Physics Letters 99 (2011)
[Copie2017] O. Copie et al., ACS Appl. Mater. Interfaces, 2017, 29311 (2017).
Technics/methods used during the internship:
X-ray photoelectron spectroscopy Photoemission electron microscopy

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