Arun Kuruvila - ESR 9, June 2018 - May 2021
University of Leeds, Leeds, UK
Master thesis: "Doped graphene as transparent electrode in organic light emitting diodes"
Graphene is a 2D material with unique electro-optical properties that let to tremendous developments of new applications. One of the most promising is the use as flexible transparent electrode and as a replacement for brittle ITO to enable next generation flexible devices like organic light emitting devices (OLEDs). In this study graphene is tailored to meet the requirements of an OLED electrode. In this process, one of the main constraints is the energy barrier between a graphene electrode and an organic layer which restrict the carrier injection. To overcome this, an effective doping of graphene and interface engineering is developed. Recently transition metal oxides (TMOs) are introduced to effectively p-dope graphene via a surface charge transfer process. It has been shown that MoO3 is a strong p-type dopant. However, the doping stability remained somewhat unclear. Here, the doping of the TMOs MoO3, WO3 and V2O5 are studied in detail by investigating not only the doping efficiency but also the doping stability. It is shown that the doping drastically lowers the sheet resistance. In addition an efficient hole injection is achieved. Based on the result, doped graphene electrodes are integrated in OLEDs and compared to the state-of-the-art ITO electrodes. The graphene based OLED show a superior efficiency compared to the reference device demonstrating that this doping concept can be used to realize novel OLED applications. Philips research, Aachen, Germany
Personal Training Committee
Main Supervisor: Chris Marrows, LEEDS
Co-supervisor: Thomas Ihn, ETH Zürich
Mentor: Axel Rudzinski, RAITH
At ETH (October 2018) for training in fabrication and contacting of devices from InAs/GaSb wafer,
At RAITH (July/August 2019) for training in nanofabrication & experience of the private sector,
At AALTO (cancelled because of the pandemic) for training in ultralow temperature techniques and low noise measurements.
Spin-polarised transport in InAs/GaSb coupled quantum well topological edge states
Objectives: The main objective of this project is to measure directly and exploit the perfect spin-polarisation of currents carried by the edge states in InAs/GaSb quantum spin Hall systems, which arises through spin-momentum locking. This system is a two-dimensional topological insulator (TI). QSHE devices will be fabricated from InAs/GaSb coupled well structures and will measure them in the quantum spin Hall state. Material growth, device fabrication and gating protocols will be developed in strong collaboration with ETH, where such expertise already exists. Using non-magnetic contacts with a large spin Hall angle (e.g. Pt) grown in LEEDS, it will be possible to detect the spin polarisation of the edge state current through the inverse SHE effect, since it interconverts between spin and charge currents. Through attaching contacts with different spacings, ESR9 will measure the length over which the edge state current is coherent. This will set the scale at which a system of devices that exploit this effect must be manufactured. Meanwhile, if current is driven between two ferromagnetic contacts (e.g. NiFe) that are separated by less than this length, a diode-like response should be found where different conductances are measured in different directions, since the spin-polarisation of the contacts defines a unique direction of current flow in the QSHE system. The ratio of conductances in the forward and reverse bias directions will provide a measure of the spin-polarisation of the carriers