Fermi level influence on the adsorption at semiconductor surfaces - ab initio simulations

TL;DR

This study investigates how the Fermi level influences chemical adsorption energies at semiconductor surfaces, revealing that for pinned surfaces adsorption energy is Fermi level independent, while for nonpinned surfaces it varies with doping, confirmed by DFT simulations.

Contribution

It demonstrates the Fermi level dependence of adsorption energy at semiconductor surfaces and clarifies the conditions under which doping affects adsorption, supported by ab initio DFT simulations.

Findings

Adsorption energy at pinned surfaces is Fermi level independent.

Adsorption energy at nonpinned surfaces depends on Fermi level position.

Doping can change adsorption energy by about 2 eV at GaN surfaces.

Abstract

Chemical adsorption of the species at semiconductor surfaces is analyzed showing the existence of the two contributions to adsorption energy: bond creation and charge transfer. It is shown that the energy of quantum surface states is affected by the electric field at the surface, nevertheless the potential contribution of electron and nuclei cancels out. The charge transfer contribution is Fermi level independent for pinned surfaces. Thus for Fermi level pinned at the surface, the adsorption energy is independent on the Fermi energy i.e. the doping in the bulk. The DFT simulations of adsorption of hydrogen at clean GaN(0001) and silicon at SiC(0001) surfaces confirmed independence of adsorption energy on the doping in the bulk. For the Fermi level nonpinned surfaces the charge contribution depends on the position of Fermi level in the bulk. Thus adsorption energy is sensitive to change of the Fermi energy in the bulk, i.e. the doping. The DFT simulations of adsorption of atomic hydrogen at 0.75 ML hydrogen covered GaN(0001) surface confirmed that the adsorption energy may be changed by about 2 eV by the doping change from n- to p-type.