Electronic Structure of AlAs Nanocrystals

Haider I Isa,Ahmed M Abdul-Lettif

doi:10.5923/j.ajcmp.20120204.02

Haider I Isa, Ahmed M Abdul-Lettif

Open Access

https://doi.org/10.5923/j.ajcmp.20120204.02

Copy DOI

Abstract

Ab initio restricted Hartree-Fock method within the framework of large unit cell formalism is used to investigate the electronic structure of the core and oxidized surface of AlAs nanocrystals. Large unit cells of 8, 16, 54, 64 and 128 atoms are used in the present analysis. Calculations are performed utilizing the Gaussian (03) software. The investigated properties include the cohesive energy, energy gap, valence bandwidth, conduction bandwidth and the density of states of the energy levels. Interesting results are obtained which reveal that the electronic structure of AlAs nanocrystals differs significantly from that of the bulk AlAs crystal. Also, it is found that the energy gap, valence band width and cohesive energy (absolute value) increase as the AlAs large unit cell size increases, for the core part. Whereas, the energy gap of oxygenated (001) - (1Ã1) surface decreases with increasing the large unit cell size. The energy gap is controlled by the surface part of the nanocrystal. The surface part has lower symmetry than the core part with smaller energy gap and wider valence bandwidth. The density of states of the core part is higher than that of the surface part. This is due to the broken bonds and the discontinuity at the surface and the existence of new kind of atoms (oxygen atoms). The present method has threefold results: the method can be used to obtain the converged electronic structure of bulk, surface, and nanocrystals.

Highlights

Aluminiu m arsenide (AlAs) is a co mpound semiconductor with an indirect band gap and it has a zinc-b lend structure[1]
Shima za ki and Asai[5] studied the energy band structure of Si, AlP, AlAs, GaP and GaAs using screened Hartree–Fock exchange method, and they found that the direct and indirect band gaps don't agree with experimental va lues
We show that the cohesive energy and valence band width increase with increasing the number of atoms per (LUC), reach ing to 64 ato ms in which they tend to stabilize, with the increasing number of atoms as shown in Fig. (2) and Fig. (3) respectively

Summary

Introduction

Aluminiu m arsenide (AlAs) is a co mpound semiconductor with an indirect band gap and it has a zinc-b lend (zb) structure[1]. Alu min iu m arsenide has been intensively investigated in the recent years, where Bouarissa and Boucenna[3] studied the electronic, optical and mechanical properties of AlAs and they showed that the results are in agreement with the availab le experimental and theoretical data. Chimata[4] studied theoretically the electronic structure of alu miniu m arsenide crystal, and they found that the band gap value obtained is in good agreement with the e xperimental value. Shima za ki and Asai[5] studied the energy band structure of Si, AlP, AlAs, GaP and GaAs using screened Hartree–Fock exchange method, and they found that the direct and indirect band gaps don't agree with experimental va lues.

Objectives

Results

Conclusion