Modification of Band Alignment via Work Function Control

Abstract

This chapter discusses modification of band alignment via work function control in an ideal case. Relationship between Schottky barrier height at the metal–semiconductor interface and the work function of the metal is explained. Some experimental examples of the relationship are demonstrated. For field-effect transistors, flat band voltage instead of Schottky barrier height is used to characterize the band alignment. Flat band voltage is expressed by the work functions of gate metal and semiconductor. Some experimental examples are demonstrated. Formation of interface dipole at metal–metal interface is explained and compared with interface dipole at metal–semiconductor interface. Parameters are introduced to describe the deviation from ideal case in the relationship between Schottky barrier height or flat band voltage and the work function, S factor and effective work function. Examples of band alignment modification are presented for both Schottky barrier height and flat band voltage, where work function is controlled either by mixing elements or by interface termination. Effective ways of modification by inserting interface layers and by interface segregation are also explained. Examples of interface layer insertion in MOSFET are demonstrated. The effectiveness and potential problems of utilizing this modification method are discussed.