5.1.2.5 Effect of the Carrier Mass on the Channel Tunneling

Being the parameter with the highest uncertainty, the electron and hole mass in the dielectric is commonly used as a fitting parameter to reproduce measurements. Its influence on the gate current density is shown in Fig. 5.7. An increase in the carrier mass by 0.1m$_0$ leads to a reduction in the gate current density by about a factor of 10. It must, of course, be held in mind that with the approaches described in Section 3, tunneling is described by a single value for the carrier mass. Its use as a fitting parameter may thus well be justified. Recent investigations, however, report an increase of the electron mass with reducing thickness of the dielectric layer, which is backed by measurements and tight-binding band structure calculations [252,253,254].

Figure 5.7: Effect of the carrier mass 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