Structural Stability of GaAs Nanocrystal Anurag Srivastava, Neha Tyagi, and R. K. Singh Citation: AIP Conf. Proc. 1349, 317 (2011); doi: 10.1063/1.3605862 View online: http://dx.doi.org/10.1063/1.3605862 View Table of Contents: http://proceedings.aip.org/dbt/dbt.jsp?KEY=APCPCS&Volume=1349&Issue=1 Published by the AIP Publishing LLC.
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Structural Stability of GaAs Nanocrystal Anurag Srivastava1*, Neha Tyagi1 and R.K. Singh2 1
Advance Material Research Laboratory, ABV-Indian Institute of Information Technology and Management, Gwalior (M.P.) 474010, India 2 School of Basic Sciences, ITM University, Gurgaon, (HRY.) 122017, India *
[email protected]
Abstract. We have used the first principle density functional approach for analyzing the structural stability of GaAs nanocrystal (NC) in various possible phases like wurtzite (B4), NiAs (B8), zincblende (B3), CsCl (B2) and NaCl (B1). The study reveals that the stable B3 phase of bulk GaAs is unstable in its nanocrystal and better stabilizes in wurtzite (B4) type phase. The study has been performed using local density approximation (LDA) with the Perdew-Zunger(PZ) parameterization and Perdew-Burke-Ernzerhof(PBE) and Revised Perdew-Burke-Ernzerhof (revPBE) parameterization of the GGA potential. The calculated lattice parameter of bulk GaAs is in close agreement with its experimental counterpart. Keywords: GaAs, Nanocrystal, DFT, lattice parameter PACS: 71.55.Eq; 71.15.Mb; 61.46.Hk; 71.15.Nc
simulations are expected to play an important role in elucidating these mechanisms. The success of ab-initio methods in predicting the high pressure behaviour of variety of materials and importance of nanocrystals has boosted us to perform this particular study.
INTRODUCTION The structural stability of III-V semiconductor compounds has been of great interest to the experimental and theoretical researchers. Due to the unique electronic and optical properties of the materials at reduced dimensions, the semiconductor nanocrystals have got much attention in recent years. These semiconductor nanocrystals have been used for wide range of applications, ranging from lasers [1], solar cells [2] to single electron transistors [3]. The bulk gallium arsenide (GaAs) has been found to undergo a transformation from the fourfold coordinated zinc blende structure to a sixfold coordinated orthorhombic structure at low pressure [4] while it further transform to eight-fold coordinated CsCl (B2) structure at comparatively high pressure[5]. Recently Kodiyalam et al. have studied structural transformation in GaAs nanocrystal under pressure using molecular dynamics simulations on parallel computers [6]. Pioneering high-pressure experiments on semiconductor nanocrystals have been carried out by Alivisatos and co-workers [7,8] to investigate the effect of finite size on the solid-solid phase transformation and to explore the possibility of stabilizing bonding geometries that are different from the corresponding bulk. The microscopic mechanism of the structural transformation in nanocrystals is, however, not completely understood and atomistic
COMPUTATIONAL BRIEF Structural stability of GaAs nanocrystal (NC) in different possible phases like wurtzite (B4), NiAs (B8), zincblende (B3), CsCl (B2) and NaCl (B1) have been performed by using atomistix toolkit (ATK). The calculation has been performed using density functional theory (DFT) in the local density approximation (LDA). The Perdew Zunger(PZ) energy functional has been used to approximate the exchangecorrelation energy. The study has been made in self consistent manner using steepest descent geometric optimization technique with pulay algorithm for iteration mixing. All the atoms are fully relaxed to change their position and geometry has been optimized until the maximum force on each atom become ≤ 0.05eV/Å.
RESULT AND DISCUSSION We have analysed the Stability in all the five possible phases of GaAs nanocrystal such as wurtzite (B4), NiAs (B8), zincblende (B3), CsCl (B2) and NaCl
Solid State Physics, Proceedings of the 55th DAE Solid State Physics Symposium 2010 AIP Conf. Proc. 1349, 317-318 (2011); doi: 10.1063/1.3605862 © 2011 American Institute of Physics 978-0-7354-0905-7/$30.00
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(B1). The total energy computation shows that the B3 phase of bulk GaAs more stable with -568.58eV, whereas the same structure is not stable in reduced dimension of host material. Interestingly the nanocrystal of GaAs shows better stability in B4 type phase at lower pressure in contrast to B3 phase its bulk. The computation finds that the lattice parameter for the bulk GaAs material in B3 phase is 5.69 Å shows a close match with its experimental counterpart [9]. We have also tested the stability of these two categories of GaAs, i.e. bulk and nano in other possible phases like B4, B8, B3, B1 and B2 type and found that the trend of total energy in case of bulk GaAs goes like B3
