This thesis presents experimental studies of two fundamental components of electronic devices: an oxide- and metal-semiconductor interface. The importance of these interfaces increases continuously when a device size is decreased, and energy-efficiency as well as durability of the devices are increased. It is challenging, however, to characterize the interface properties on atomic level because of their hidden nature beneath the metal or oxide film. Moreover, because the semiconductor surface interacts with oxygen and metal elements during the fabrication of these junctions, electronic defect states form at the interface, lowering device efficiency and durability.

This study focuses on modification and characterization of the following Si(100) and InP(100) semiconductor interfaces: (i) nitridation of HfO2/Si(100) interfaces, (ii) native oxide modification on n- and p-InP(100), and (iii) Ni/p-InP(100) interface with magnesium surface doping.

The interface properties have been studied by complementary surface-science and electrical methods: scanning tunnelling microscopy/spectroscopy, low energy electron diffraction, X-ray photoelectron spectroscopy, and photoluminescence along with electrical measurements like capacitance-voltage, current-voltage, and contact resistivity. Most interface modifications have been done in ultrahigh-vacuum (UHV) chambers in controlled environments.

The experimental results show that (i) NH3 nitridation of Si(100) at low temperature reduces the interface defect density at the HfO2/Si(100) junction, (ii) a proper low temperature gas-based treatment (NH3 or O2) improves the quality of the InP native-oxides by reducing the harmful surface defects, and (iii) proper wet chemically treatment combined with UHV-based InP surface modification can reduce the contact resistivity at p-InP contacts.