Passivation of Ge(100) and (111) Surfaces by Termination of Nonmetal Elements

The passivation of the Ge surface is an important issue for a high-performance transistor. Therefore, we carried out the theoretical and experimental analyses to search for alternative terminal materials on the Ge surface. First, the chemical reactivities of various nonmetal elements on the Ge surface were simulated by the semi empirical molecular orbital method to passivate the Ge(100) and (111) surface dangling bonds. The simulations showed that F, Cl, and Se are more useful for the treatment of the Ge(100) surface and that F, Cl, S, and Se are more stable on the Ge(111) surface than H. In particular, S is more effective in terminating the dangling bonds by forming a bridge bond (Ge--S--Ge) and more stable on the Ge(111) surface than on the Ge(100) surface. Next, for experimental confirmation, we performed an (NH 4 ) 2 S solution treatment method on the p-type Ge(100) and (111) substrates, and fabricated HfO 2 /p-Ge metal--insulator--semiconductor (MIS) devices by photo assisted metal organic chemical vapor deposition (MOCVD). As a result, the S-treatment using (NH 4 ) 2 S solution improved more the electrical properties of the HfO 2 /p-Ge(111) MIS capacitor than those of the capacitor on the Ge(100) substrate. Recently, the sulfur treatment of the Ge surface has been mainly focused on the Ge(100) substrate. However, the results of this study show that the sulfur treatment method using (NH 4 ) 2 S solution is more useful on the Ge(111) surface than on the Ge(100) surface.