Adsorption and diffusion of 3d transition metal atoms on the GaN(0001) surface

Abstract

We carried out first-principles spin-polarized calculations in order to study the adsorption and diffusion of 3d transition metal (TM = Ti, V, Cr, Mn, Fe, Co, and Ni) atoms on a GaN(0001)- 2×2 surface using density functional theory within a plane-wave ultrasoft pseudopotential scheme. The results show that, for Ti, V, Cr, and Mn atoms, the most stable adsorption sites are all at the T4 site (the top site of the N-surface atom), whereas Fe, Co, and Ni slightly prefer the H3 hollow site. The adsorption energies can vary significantly with different TM atoms. A comparative study suggests that the TM–N bond formation is energetically more favorable for Ti, V, and Cr atoms, while the formation of a TM–Ga surface alloy is more favorable for elements such as Fe, Co, and Ni, as experimental results have shown. We found that the 3d TM adatom diffusion energy barrier between the H3 and T4 sites is around 0.40 eV, which is an indication of a significant TM adatom diffusion on the GaN(0001) surface. Furthermore, the total magnetic moment increases for Ti, V, Cr, and Mn adsorbates successively and then decreases for Fe, Co, and Ni adsorbates. The density of states indicates that the adsorption of Ti, V, and Cr atoms results in semiconductor behavior, while the adsorption of Mn, Fe, and Co atoms presents a half-metallic character. These properties make the TM/GaN systems promising for yielding high-efficiency metal-semiconductor spin injection devices.

In situ microbeam surface X-ray scattering reveals alternating step kinetics during crystal growth

“…To interpret the combined parameters obtained from the fits, it is useful to estimate the adatom diffusivity D and equilibrium adatom density . Ab initio calculations of the activation energy for Ga diffusion on the Ga-terminated (0001) surface have given values of Δ H m = 0.4 43 and 0.5 eV 44 , and similar values have been obtained for 3 d transition metal adatoms 45 . If we estimate the diffusivity from the ab initio calculations using 46 , with a = 3.2 × 10 −10 m, ν = 10 13 s −1 , Δ S m = 0, and Δ H m = 0.4 eV, we obtain D = 1.4 × 10 −8 m 2 s −1 at T = 1073 K. An analysis of spatial correlations in surface morphology of GaN films 47 indicated a cross-over at T = 1073 K from surface diffusion transport to evaporation/condensation transport at a length scale of λ = 1.5 × 10 −6 m for OMVPE growth with H 2 present in the carrier gas.…”

A comparative DFT study of the structural and electronic properties of nonpolar GaN surfaces

“…Surface energies are important for predicting the shapes of nanostructures and identifying the faceting and roughening of surfaces. Therefore, considerable theoretical and experimental efforts have been devoted to them, in order to gain insight into the structural and electronic properties of the GaN surface, in particular for the polar (c-plane) surface [13][14][15][16]. Comparatively little progress has been made in the understanding of the geometric and electronic characteristics of nonpolar GaN surfaces and the subsequent growth process on such surfaces at the atomic level.…”

Hydrogen Gas Adsorption on Pd‐ and Pt‐Decorated GaN (0001) Surface: A First‐Principles Study

“…This means that Pd and Pt atoms are prone to be dispersed on the GaN (0001) surface. The calculated results are similar to those of other 3d transition metal atoms on the GaN surface . Then, we analyze the structural characteristics of Pd and Pt atoms adsorption on GaN (0001).…”