The PhD defence and trial lecture are partly digital and streamed using Zoom. The chair of the defence will moderate the disputation.
Ex auditorio questions: the chair of the defence will invite the audience physically present in the auditorium to ask ex auditorio questions.
→ Live streaming of trial lecture and disputation
→ Request for thesis copy (available until the disputation starts)
Trial lecture
Time and place: June 13, 2023; 10:15 AM, Lille Fysiske auditorium (V232) - Fysikkbygningen
Title: "Wide band gap radiation detectors: devices and applications"
Main research findings
A multitude of today's electronic devices require a material which is both optically transparent and electrically conductive in order to operate as intended. Several such materials have been developed, and are technologically well understood. However, there are still unanswered questions related to how these materials behave on the nanoscale. While it is well known that defects in the atomic structure are crucial for the electronic properties of these materials, exactly which defects are important and how they interact is generally not known. This thesis explores how the electrical resistivities of a selection of transparent conductive materials change when defects are introduced into their atomic structures via ion irradiation. Compelling evidence is found for three individual effects: At low ion doses, atoms and molecules which have adsorbed to the material surface from exposure to the ambient are removed, recovering the native surface structure. As the dose is increased, individual bulk point defects are formed in sufficient concentrations to affect the resistivity, and at yet higher doses, these defects can combine into defect complexes. Each of these three effects have the potential to significantly change the resistivity, and have been compiled into a general model which is applicable to any semiconductor material.
Hovedfunn (Norwegian)
I mange av dagens elektronikkprodukter trengs det et materiale som er både gjennomsiktig og strømførende. Flere slike materialer har blitt utviklet, og disse er godt forstått fra et teknologisk synspunkt. Imidlertid er det fremdeles flere ubesvarte spørsmål relatert til hvordan disse materialene oppfører seg på nanoskala. Det er velkjent at defekter i atomstrukturen er kritiske for de elektroniske egenskapene til slike materialer, men eksakt hvilke defekter som bidrar, og hvordan de interagerer er ikke fullt ut forstått. I denne avhandlingen viser vi hvordan den elektriske resistiviteten til utvalgte transparente ledende materialer endres når defekter introduseres gjennom ionebestråling. Tre individuelle effekter har blitt avdekket: Ved lave ionedoser fjernes atomer og molekyler som har adsorbert på overflaten. Når dosen økes noe genereres det individuelle punktdefekter i tilstrekkelige konsentrasjoner til å endre resistiviteten, og ved ennå høyere doser vil disse defektene kunne reagere og danne ulike komplekser. Hvert av disse bidragene kan gi betydelige endringer i resitiviteten, og har blitt sammenfattet i en generell modell som kan benyttes på alle halvledende materialer.
Adjudication Committee
- Professor Farida Selim, Physics and Astronomy Department, Bowling Green State University, USA
- Professor emeritus George Kiriakidis, Department of Physics, University of Crete, Greece
- Professor Ketil Røed, Department of Physics, University of Oslo, Norway
Supervisors
- Professor Andrej Kuznetsov, Department of Physic, University of Oslo, Norway
- Dr. Klaus Magnus Håland Johansen, Department of Physic, University of Oslo, Norway
- Dr. Helge Kristiansen, Conpart AS, Norway
Chair of defence
- Professor Andreas Görgen, Department of Physics, University of Oslo, Norway
Contact information to Department: Line Trosterud Resvold