Surface and interface characterization studies of germanium and indium arsenide substrates

This thesis investigates the surface cleaning procedures, passivation and interface formation following high-κ deposition on Ge(100) and InAs(100) substrates using soft x-ray photoemission spectroscopy (SXPS). A comparison study between the thermal cleaning of the native oxide covered InAs(100) surface and atomic hydrogen cleaned surface indicated that thermal annealing to 450oC is not sufficient to produce an oxide and carbon free surface whereas atomic hydrogen cleaning at 360oC resulted in the removal of both native oxides and surface carbon contamination to produce a clean In rich surface. The selenium passivation of this atomically clean InAs showed evidence of arsenic replacement in the near surface region. Subsequent MgO deposition resulted in interface oxidation indicating that the selenium treatment has not been successful in passivating the InAs surface. In a similar study on the atomically clean Ge(100) surface, interface oxide formation was observed following MgO deposition while on the selenium passivated surface, no interface oxides were observed. Wet chemical sulphur treatments of both the Ge(100) and InAs(100) surfaces showed that the sulphur passivation layer was stable up to 500oC and 600oC, respectively. Subsequent studies involving the atomic layer deposition of ultra thin high-κ dielectric layers on these surfaces showed that thermal annealing was effective at reducing the interfacial oxides without altering the dielectric material’s stoichiometry. The high pressure post oxygen annealing treatment of Al2O3/Ge structures were chemically characterised using SXPS and x-ray photoelectron spectroscopy (XPS), and electrically tested after fabricating MOS capacitor structures. The density of interface states (Dit) was significantly decreased when the Ge(100) surface was subjected to wet chemical based sulphur treatments prior to dielectric deposition. Finally, the concentrations of germanium sulphide formation on the Ge(100) surface achieved by diluting ammonium sulphide in various alcohols was studied using SXPS and the electrical impact on the CV measurements of MOS structures on these surfaces was investigated