UC San Diego

Gas and oxide adsorption and their impact on the properties of semiconductor interfaces were investigated at the atomic level with both experimental and theoretical techniques. Two types of semiconductors were studied, an organic semiconductor, employed in chemical field effect transistors (chemFETs) and alternative channel materials for metal oxide field effect transistors (MOSFETs). Adsorption of nitric oxide (NO) on iron phthalocyanine (FePc), an organic semiconductor, was explored to determine the adsorption mechanism of NO. King and Wells sticking measurements were performed on ordered monolayer, multilayer FePc and quasi-amorphous tetra-t-butyl FePc multilayer thin films to determine the impact of surface order and thickness on adsorption. Density functional theory (DFT) results show there is a deep chemisorption well at the metal center. The metal centers are a small fraction of the surface (3%), but the initial sticking probability was 40% at low surface temperature and low incident beam energy. Both the experimental and theoretical data supports molecular NO sticking onto FePc via physisorption to the aromatic periphery followed by diffusion to the Fe metal center, a multiple pathway precursor-mediated chemisorption. To understand the chemical dynamics of bonding at the oxide/semiconductor interface, the adsorption of oxygen, nitrogen, and high- [kappa] dielectrics onto alternative high mobility channel materials, Ge and InAs, was investigated to identify passive oxide/semiconductor interfaces via DFT. DFT modeling of experimental results found oxygen exposure on Ge(0 0 1)-(4 x 2) pins the Fermi level near the valence band due to generation of Ge ad-atoms and formation of a suboxide. Similarly, DFT modeling demonstrated that the nitrided Ge(001) surface was pinned due to generation of Ge ad-atoms and formation of a subnitride. For III-V materials, a comparison was made of the geometric and electronic structures of ordered HfO₂ and ZrO₂ monolayers on InAs(0 0 1)-(4 x 2). DFT calculations showed that both high-k oxides were able to electronically passivate the InAs(0 0 1)-(4 x 2) surface, decreasing density of states at the Fermi level by removal of dangling bonds and strained bonds on the semiconductor substrate. With a greater atomic understanding of the oxide-semiconductor interfaces, the presented results can help guide future device engineering efforts