Density functional calculations of the binding energies and adatom diffusion on strained AlN (0001) and GaN (0001) surfa
- PDF / 2,604,343 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 88 Downloads / 215 Views
1040-Q06-02
Density functional calculations of the binding energies and adatom diffusion on strained AlN (0001) and GaN (0001) surfaces Vibhu Jindal, James Grandusky, Neeraj Tripathi, Mihir Tungare, and Fatemeh Shahedipour-Sandvik College of Nanoscale Science and Engineering, University at Albany, 255 Fuller Road, Albany, NY, 12203 ABSTRACT Density functional calculations were carried out to study the binding energies and diffusion barriers of various adatoms on AlN and GaN (0001) surfaces. The binding energies and potential energy surfaces were investigated for Al, Ga, and N adatoms on both Al (Ga) terminated and N terminated (0001) surfaces of AlN (GaN). Calculations were performed to investigate the diffusion paths and obtain diffusion energy barriers of these adatoms. It was found that the N adatom on N terminated AlN and GaN surfaces faces a high diffusion barrier due to strong N-N bond. The Al and Ga adatom on Al (Ga) terminated AlN (GaN) surfaces showed lower diffusion barriers due to the weak metallic bonds. However, the diffusion barrier for an Al adatom was always larger than that of a Ga adatom on any surface. To investigate the effect of strain on diffusion barriers the surfaces were subjected to a hydrostatic compressive and tensile strain in the range of 0 to 5%. The diffusion energy barrier for N adatom on N terminated AlN and GaN surfaces decreased when the strain state was changed from tensile to compressive. In contrast, Al and Ga adatoms show continuous increase in diffusion barriers from tensile to compressively strained Al (Ga) terminated AlN (GaN) surfaces. INTRODUCTION III-Nitride based devices have become very important in the past decade for applications in optoelectronic and electronic devices [1]. Although, there has been great progress on epitaxial growth of high quality AlInGaN device structures, deeper fundamental understanding of the growth mechanisms for homoepitaxy and heteroepitaxy of such layers is required [2-3]. Considerable theoretical efforts have been made in order to gain insight on physical processes such as adsorption, desorption, and diffusion of various adatoms on clean and adsorbate-covered GaN surfaces [4-6]. However, the influence of strain on such physical processes in III-Nitride systems is not very well known. The effect of strain on surface diffusion properties is not only of general scientific interest but also of technological importance. Strain plays an important role in any lattice mismatched heteroepitaxial growth system [7-8]. Phenomena occurring due to strain such as formation of quantum dots and nanostructures (transition of growth mode from 2D to 3D), coarsening of 2D island arrays, alloy fluctuation and phase ordering, emphasize the role of strain in a heteroepitaxial system [9-13]. Understanding of the effect of strain is also essential in homoepitaxy as the substrates often contain large impurity concentrations and residual strain [14]. This has driven the focus towards the development of a fundamental understanding of the effect of strain on kinetic p
Data Loading...
