5.1.2.4 Effect of the Barrier Height on the Channel Tunneling

The main parameter, besides the thickness of the dielectric, influencing tunneling current is the height of the energy barrier. The influence of this parameter is depicted in Fig. 5.6. Different dielectric materials strongly differ in their work function difference to silicon. It must be distinguished between the barrier height for electrons and for holes. The most frequently used dielectric material SiO$_2$ has an electron barrier height of about 3.2eV and a hole barrier height of approximately 4.6eV. The measurement of these material parameters is difficult and values in the available literature vary widely (see Section 5.1.5).

Figure 5.6: Effect of the electron and hole barrier height on electron tunneling current (left) and hole tunneling current (right) in an nMOS (top) and a pMOS (bottom) with 2 nm dielectric thickness, 1e20 cm-3 polysilicon and 5e18 cm-3 substrate doping.

A. Gehring: Simulation of Tunneling in Semiconductor Devices