Hole Transport in SiGe

Hole transport in SiGe alloys from first principles
The hole mobility in SiGe as a function of Ge content.
The hole mobility in SiGe as a function of Ge content.

We are interested in investigating the transport properties of carriers in SiGe alloys in the presence of alloy disorder. By understanding the scattering rates and thus the carrier mobility, we aim to provide valuable insight into properties relevant to device design. We combine Density FunctionalTheory (DFT) and scattering theory to calculate the hole mobility from first principles. The alloy is modelled within the virtual crystal approximation (VCA) using supercell techniques and the disorder is simulated by the addition of Si and Ge defects. The scattering matrix for hole scattering in the presence of the disorder is determined from the resultant energy splitting in the valence bands. The mobility is obtained from the scattering rate using the Boltzmann transport equation in the relaxation time approximation. The graph illustrates the total hole mobility in the presence of alloy scattering in bulk unstrained Si1-xGex compared with experiment. The phonon limited mobility was obtained empirically by Fischetti and Laux [1].

[1] M. Fischetti and S. Laux, J. App. Phys. 80 (1996) 2234.

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