Interface Trap Characterization and Fermi Level Pinning in Si-Passivated Ge/HfO2 Capacitors

Abstract

Recently germanium MOSFETs have attracted attention due to the promising carrier mobility of germanium compared to silicon. To understand the germanium MOSFET interface, the conductance interface trap density extraction technique was verified for the first time on germanium MOSFETs. In order to know the characteristics of the (near-) interface traps it is essential to confirm the validity of the model on which their extraction is based. It cannot be simply assumed that the interface will behave as in Si. For this purpose low temperature measurements were performed at 80 K and a variation on the ac conductance technique was developed. Typical Si impedance behavior is found for Ge but Si extraction methods cannot be applied to Ge capacitors in general. Indications for weak Fermi-level pinning near the conduction band were found in Si-passivated Ge/HfO2 capacitors. This explains the weak performance of the corresponding nMOSFET.