UC San Diego

In recent years, germanium (Ge) and silicon-germanium (SiGe) have drawn significant interest as replacements of conventional silicon in the search for alternative materials for use in complementary metal-oxide- semiconductor (CMOS) devices due to their high electron and hole mobilities. In order to effectively implement Ge or SiGe as a replacement for silicon, two major challenges must be overcome: non-disruptive cleaning and surface passivation/functionalization. As electrical devices are increasingly scaled, it becomes especially crucial to effectively clean each unit cell on the Ge/SiGe surface without causing major disruption or damage to the surface. If air-induced defects or contaminants persist on the surface after cleaning, these defect sites may be un- reactive for functionalization and thereby will hinder device performance and/or the ability to aggressively scale device size. If a cleaning method is too aggressive leaving a rough or disordered surface, this can lower the mobility at the interface which will worsen device performance. For these reasons, it is necessary to develop a non-disruptive cleaning process that cleans each unit cell leaving a flat, ordered, and reactive surface. Once the Ge or SiGe surface is cleaned, in order to achieve a good electrical quality interface and a high nucleation density on the surface, all surface atoms must be passivated and functionalized allowing for aggressive device scaling. The interface must remain electrically passive in order to not inhibit electrical performance of the device. This study uses scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and x-ray photoelectron spectroscopy (XPS) to develop and analyze a completely in-situ non-disruptive cleaning method of the Ge surface using H₂O₂(g) and atomic hydrogen. After cleaning, the Ge or SiGe surface is passivated and functionalized using H₂O₂(g) as a method to improve upon the conventional H₂O(g) passivation method by more than doubling the reactive -OH groups on the surface. Once a high density of -OH chemisorbates passivate and functionalize the surface, trimethylaluminum is dosed onto the surface forming a thermally stable and electrically passive monolayer which can serve as an ideal template for further high-k oxide deposition