Enhancement of Carrier Mobility in Semiconductor Nanostructures by Dielectric Engineering

We propose a technique for achieving large improvements in carrier mobilities in 2- and 1-dimensional semiconductor nanostructures by modifying their dielectric environments. We show that by coating the nanostructures with high-$\kappa$ dielectrics, scattering from Coulombic impurities can be strongly damped. Though screening is also weakened, the damping of Coulombic scattering is much larger, and the resulting improvement in mobilities of carriers can be as much as an order of magnitude for thin 2D semiconductor membranes, and more for semiconductor nanowires.

Figure 1

Electric flux lines originating from a fixed ionized impurity and terminating on a mobile electron, and the effect of the dielectric environment. The flux lines bunch closer inside the semiconductor layer if ${ϵ}_e<{ϵ}_s$, and spread farther apart if ${ϵ}_e<{ϵ}_s$, thus enhancing Coulomb interaction in the former case and damping it in the latter.

Figure 2

The effect of dielectric mismatch on the Thomas-Fermi screening wave vector. (a) shows that screening is stronger than the case without dielectric mismatch for ${ϵ}_e<{ϵ}_s$ for small angle scattering ($q\sim 0$), $q=k_F$, and backscattering $q=2k_F$ (for $a=1\mathrm{nm}$). When ${ϵ}_e<{ϵ}_s$, screening is weaker than the case without dielectric mismatch. (b) shows that the effect of dielectric mismatch on screening is substantial if the thickness of membrane is small.

Figure 3

(a) The variation of Coulombic scattering rate for different semiconductor layer thicknesses for a range of dielectric environments. (b) Effect of dielectric mismatch on Coulombic scattering as a function of the semiconductor membrane thickness.

Figure 4

(a) Total scattering rate due to combined surface roughness and Coulombic impurity scattering, and (b) the dependence of the total mobility for three dielectric environments on the semiconductor membrane thickness. A large increase in mobility is expected for thin semiconductor layers coated by high-$\kappa$ dielectrics.