Foundations of ab initio simulations of electric charges and fields at semiconductor surfaces within slab models

Abstract

Semiconductor surfaces were divided into charge categories, i.e. surface acceptor, donor and neutral ones that are suitable for simulations of their properties within a slab model. The potential profiles, close to the charged surface states, accounting for explicit dependence of the point defects energy, were obtained. A termination charge slab model was formulated and analyzed proving that two control parameters of slab simulations exist: the slope and curvature of electric potential profiles which can be translated into a surface and volumetric charge density. The procedures of slab model parameter control 2 are described and presented using examples of the DFT simulations of GaN and SiC surfaces showing the potential profiles, linear or curved, depending on the band charge within the slab. It was also demonstrated that the field at the surface may affect some surface properties in a considerable degree proving that verification of this dependence is obligatory for a precise simulation of the properties of semiconductor surfaces.

Adsorption of ammonia at GaN(0001) surface in the mixed ammonia/hydrogen ambient - a summary of ab initio data

“…In the recent study we have shown how the adsorption energy depends on the electric charge transfer between solid bulk or the existing surface states and the new states emerging due to the presence of the adsorbate. 5,6 It was shown that in the absence of the charge transfer the adsorption energy attains the value determined by the energy of the bonding. The novel recently introduced idea is the energy dependence on the electronic charge transfer.…”

“…The novel recently introduced idea is the energy dependence on the electronic charge transfer. 5,6 The new phenomenon originates from the fact that the exchange of the electron between the Fermi level and the emerging surface state of different energies generates an additional energy gain. The energy difference of these two states may reach several electronvolts, affecting the adsorption energy considerably.…”

“…Accordingly, the type of the surface state (donor or acceptor) 5 depends on the doping in the bulk, as shown in Fig. 1.…”

“…These investigations led not only to the considerable understanding of the system but also to the development of new methods, which are now sufficiently mature to simulate the surface taking into consideration the influence of the charged surface states and the fields close to the surface. [1][2][3][4][5][6] Recently, the dependence on the position of the Fermi energy and doping was also accounted for. 6,7 These new methods led to the discovery of new features, fundamentally changing the basic notions related to the processes occurring at the surface of a semiconductor and, introducing the dependence of adsorption energies on a pinned Fermi level surface and doping in the bulk for an unpinned Fermi level surface.…”

Multiscale approach to the electronic structure of doped semiconductor surfaces

“…The first-principles simulation of doped semiconductor surfaces has been addressed in recent literature using different approaches. Krukowski, Kempisty, and co-workers have manipulated the location or charge of passivating, back-side atoms to reproduce the effects of the SCR on the electronic structure of finite slab simulations of charged surfaces [19][20][21]. Using this, they demonstrated that the electric field of the SCR may shift surface state energies, a phenomenon that they termed the "surface-state Stark effect."…”