Doping dependence of the surface phase stability of polar O-terminated (0001̅) ZnO

Abstract

The dependence of hydrogen coverage on the bulk doping concentration is investigated for the polar O-terminated (0001̅ ) ZnO surface. We use hybrid density-functional theory in combination with ab initio thermodynamics to determine a doping-dependent phase diagram of this surface. For hydrogen coverages lower than 50% dangling oxygen bonds remain at the surface, where they subsequently become charged by bulk electrons. For such charged surfaces, a computational firstprinciples approach is presented, with which long-range band bending can now be included in firstprinciples supercell calculations. In this work, we use a modified and extended version of the recently introduced charge-reservoir electrostatic sheet technique (Sinai et al 2015 Phys. Rev. B 91 075311) to incorporate band bending effects directly into our first-principles calculations. This allows us to investigate the effect of space charge layers and the resulting band bending on the hydrogen coverage of the ZnO (0001̅ ) surface. After introducing a new implementation of CREST, we show that the structure and stability of polar ZnO surfaces are indeed sensitive to the amount of free charge carriers in the bulk. At low doping concentrations our results corroborate the previously reported (2 × 1) hydrogen phase, at higher doping concentrations the hydrogen coverage diminishes notably.

Band Bending Engineering at Organic/Inorganic Interfaces Using Organic Self‐Assembled Monolayers

“…Due to its low‐lying valence band, bulk ZnO is always found to be n‐type doped . In the present work, we use a modified version of the CREST method to account for doping . CREST treats a part of the substrate (the surface) within DFT, while the long‐range electrostatic behavior (i.e., in particular the band bending) is captured semi‐classically using a charged plate at the bottom of the slab.…”

“…[51] In the present work, we use a modified version of the CREST method to account for doping. [33,34] CREST treats a part of the substrate (the surface) within DFT, while the long-range electrostatic behavior (i.e., in particular the band bending) is captured semi-classically using a charged plate at the bottom of the slab. Within the quantum-mechanically treated substrate, we employ the virtual crystal approximation to model the free charge carriers.…”

“…[32] Band bending and doping are treated using a simplified version of the charge reservoir electrostatic sheet technique (CREST). [33,34] In short, CREST simulates the space-charge region by a negatively charged sheet placed on the backside of the slab. The charge and position of the sheet is determined self-consistently, using only the substrates doping concentration N D and its dielectric constant as parameters.…”

“…To account for long range van der Waals interactions, we used the vdW‐TS scheme with an appropriate parameterization for metal oxides . Band bending and doping are treated using a simplified version of the charge reservoir electrostatic sheet technique (CREST) . In short, CREST simulates the space‐charge region by a negatively charged sheet placed on the backside of the slab.…”

First-principles calculations of hybrid inorganic–organic interfaces: from state-of-the-art to best practice

“…One example for this is the ZnO(0001)-surface, which, depending on the sample history, may contain a different number of hydrogen or hydroxyl groups on the surface or form triangular pits with missing surface atoms. 39,101,103,[142][143][144] Like for metal surfaces, these surface modifications can substantially change the interface geometry and chemistry. 145,146 A particular challenge in this context is that adatoms or hydroxyl group are frequently not detectable in (especially LEED or STM) experiments.…”