Hommedal, Ylva Knausgård
Spectroscopic investigation of Band Alignment in Novel 2DEG devices based on κ-(MxGa1−x)2O3-alloys.
Universitetet i Oslo.
MASTER THESIS: X-ray photoelectron spectroscopy (XPS) has been used to investigate the newly identified κ-phase of Ga2O3, where the bandgaps have been tuned by alloying with Al and In, ex- panding and reducing the bandgap, respectively. The adjustable bandgaps and spontaneous polarisation make κ-(MxGa1−x)2O3 thin films with M=In, Al promising materials for a high electron mobility transistor (HEMT). In this thesis Al and In concentrations were success- fully determined with XPS in κ-(AlxGa1−x)2O3 and κ-(InxGa1−x)2O3. In κ-(InxGa1−x)2O3 UV photospectrometry (UV/vis) measurements showed that the bandgaps decrease with in- creasing x. The valence band edge in κ-(AlxGa1−x)2O3 was investigated with XPS, where the distance between the Fermi level and the valence band maximum (VBM) was shown to widen with increasing x in κ-(AlxGa1−x)2O3. In heterostructures with κ-(AlyGa1−y)2O3 and κ-(InxGa1−x)2O3, valence band offset (VBO) was determined for the first time with XPS by using the Kraut method. Discontinuities in the valence band were observed and band diagrams showed the possibility for two-dimensional electron gas (2DEG) to form on the interface with adjustments in the layer compositions. Two samples showed promising results for 2DEG to form on the interface, and for further investigation, a combination of these samples is recommended. That is y = 0.4 and x = 0.2 − 0.3 in a heterostructure with κ-(Aly Ga1−y )2 O3 /κ-(Inx Ga1−x )2 O3 .