Temperature Stabilized Surface Reconstructions at Polar ZnO(0001)

Valtiner, Markus; Todorova, Mira; Grundmeier, Guido; Neugebauer, Jörg

doi:10.1103/physrevlett.103.065502

Cited by 120 publications

(152 citation statements)

References 25 publications

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“…The choices of low energy reconstructions without H follow previous investigations [53,57,69,70]. Specifically, on ZnO polar surfaces, although several different surface reconstruction models are proposed by both theoretical calculations and experiments [53,70], the surface energy differences among them are in the order of a few meV/Å 2 [70], suggesting that the (2×2) adatom reconstruction is adequate for our discussions here. For GaN, (2×2) adatom reconstructions were taken into consideration under the condition of N-rich [57].…”

Section: Methodsmentioning

confidence: 99%

“…However, the lowest energy configurations must be those surfaces that satisfy ECR [52,56]. It demonstrated that the vibrational entropy of the surface plays a decisive role in the competition among various phases to achieve thermodynamic stability [53]. And when the temperature (and pressure) effects of the gas phase reservoirs, which arises from vibrational contributions to the entropy [56], are significant in high temperature growth, it would constrain the reconstructions within a limited number of configurations with less hydrogen atoms [56].…”

Section: Methodsmentioning

confidence: 99%

“…The accurate prediction of growth mode will need the absolute energy based on surface reconstructions. In this paper, we adopted surface reconstructions proposed by early STM observations and first principles calculations [53,57,69,70]. In this paper, we follow our cluster and pseudo molecule method [36] strictly.…”

Section: Methodsmentioning

confidence: 99%

“…During the standard OMVPE growth processes, hydrogen is a common unavoidable impurity [48,49], often decomposed from precursors or carrier gases [50]. As a result, hydrogen-involved surface reconstructions have also been reported on the polar surfaces of ZnO [51][52][53][54][55] and GaN [56,57] both in experiments and theories. Such surface reconstructions are usually stable because H may help the surface to satisfy electron-counting-rule (ECR) [58].…”

Section: Introductionmentioning

confidence: 99%

“…It's essential to perform a calculation of the vibrational entropy of H, which is the major component of the chemical potential of H during high temperature growth [52][53][54][55][56][62][63][64][65][66]. In addition to such theoretical calculation, applying the experimental Gibbs free energy of H2 is also a possible alternative method to obtain the quantitative relations of H chemical potential, temperature (T) and pressure (p).…”

Section: Introductionmentioning

confidence: 99%

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Hydrogen-surfactant-assisted coherent growth of GaN on ZnO substrate

Zhang

Tse

et al. 2018

Phys. Rev. Materials

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Heterostructures of wurtzite based devices have attracted great research interests since the tremendous success of GaN in light emitting diodes (LED) industry. Among the possible heterostructure material candidates, high quality GaN thin films on inexpensive and lattice matched ZnO substrate are both commercially and technologically desirable. However, the energy of ZnO polar surfaces is much lower than that of GaN polar surfaces. Therefore, the intrinsic wetting condition forbids such heterostructures.As a result, poor crystal quality and 3D growth mode were obtained. To dramatically change the growth mode of the heterostructure, we propose to use hydrogen as a surfactant, confirmed by our first principles calculations. Stable H involved surface configurations and interfaces are investigated, with the help of newly developed algorithms. By applying the experimental Gibbs free energy of H2, we also predict the temperature and chemical potential of H, which is critical in experimental realizations of our strategy. This novel approach will for the first time make the growth of high quality GaN thin films on ZnO substrates possible. We believe that our new strategy may reduce the manufactory cost and improve the crystal quality and the efficiency of GaN based devices.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Hydrogen-surfactant-assisted coherent growth of GaN on ZnO substrate

Zhang

Tse

et al. 2018

Phys. Rev. Materials

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Handling Time and Temperature in Materials Simulations

Todorova

2012

Characterization of Materials

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Presented is an approach based on the seamless transmission of information obtained from modern electronic structure methods like density‐functional theory to thermodynamic functions. It allows to circumvent short term dynamics in a system, instead focusing on the long‐term impact an environment can have on it. It allows the identification of stable and metastable phases at relevant ( T,p )‐conditions. After outlining the basic principles of the methodology, examples of surfaces in contact with realistic environments are used to emphasise or illustrate different aspects of the method. Particular attention is paid to possible approximations and their justification is discussed. The use of a direct screening approach, in which relevant structures are directly compared, as a possibility to deal with the configurational diversity of a system is discussed. Its advantages and disadvantages are discussed, and alternative routes are suggested. The importance of surface vibrational entropy is discussed in some depth, since it can have a large impact on formation Gibbs free energies and thus on the competition between relevant structures to gain thermodynamic stability at a given temperature. The assumption underlying the thermodynamic approach are reviewed and routes to extend the thermodynamic formalism to account for kinetically stabilised surface reconstructions are presented. Experimental situations, which may give rise to chemical potentials beyond the thermodynamic limit are mentioned. Examples of equilibrium, extended and meta‐stable surface phase diagrams are shown and discussed.

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Structure and Stoichiometry Prediction of Surfaces Reacting with Multicomponent Gases

Herrmann

Heimel

2014

Advanced Materials

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Reactive interactions of molecules with solid surfaces are of key interest for catalysis and surface functionalization. Here, conceptual shortcomings of previous theoretical methods for the prediction of steady-state surface structures and stoichiometries from first-principles thermodynamics are identified. An extension is then proposed, which now enables the unconstrained description of an arbitrary number of mutually reacting gas-phase species.

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Temperature Stabilized Surface Reconstructions at Polar ZnO(0001)

Cited by 120 publications

References 25 publications

Hydrogen-surfactant-assisted coherent growth of GaN on ZnO substrate

Hydrogen-surfactant-assisted coherent growth of GaN on ZnO substrate

Handling Time and Temperature in Materials Simulations

Structure and Stoichiometry Prediction of Surfaces Reacting with Multicomponent Gases

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