Abstract
In this thesis we study the influence to the thermal stabilities and conduction of oxidized AlAs/GaAs interface. The surface morphology and Raman spectra are obtained by varying the oxidation time and in-situ annealing to deduce the oxidation mechanism and the reason for delemination. The conduction and interface-state properties of oxidized AlAs are investigated by varying the oxidation time using current-voltage (I-V), capacitance voltage (C-V) measurements. We first grew epitaxial structures with different AlAs thickness for oxidation experiment. Data are presented demonstrating that the lateral wet oxidation of AlAs layer is strongly influenced by its thicknesses. The oxidation length decreases rapidly with decreasing AlAs thickness. At 460℃ the oxidation length of 100-nm-thick AlAs layer is over 8 times longer than that of 30 nm thick AlAs layer. Then the thermal stability of the AlAs layer with different oxidation time is studied by Raman spectroscopy and Nomarski microscopy. We find that the thermal stability of the mesas depends strongly on the desorption of As and As2O3. Thermally stable oxide layers can be achieved when volatile intermediates in the oxides are removed by either elongating thermal oxidation or in situ annealing of partially oxidized AlAs layers. We use three devices with different oxidation time to carry on C-V and I-V measurements. With short oxidation time, CV spectra show a constant capacitance without any frequency dispersion, implying defect free AlAs /GaAs interfaces. For longer oxidation, C-V spectra show frequency dependent characteristics, consistent with the presence of interface states between oxidized-AlAs/GaAs. However, I-V characteristic of incompletely oxidized devices shows that the oxidation layer is not enough to effectively block the current flow. Effective current blocking is achieved for increasing time to complete oxidation. Besides the interface states, we observe a presence of significant fixed charge for such oxidized devices.