Preparation, Structure, and Electronic Properties of Amorphous Gaas by Tight-Binding Molecular Dynamics
- PDF / 347,088 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 57 Downloads / 211 Views
Dipartimento di Fisica - Universita di Milano, via Celoria 16, 20133 MILANO (Italy)
ABSTRACT
We investigate the short-range structural properties of a-GaAs as obtained in a computer experiment based on a tight-binding molecular dynamics simulation. The amorphous configuration is obtained by quenching a liquid sample well equilibrated at T=1600 K. A detailed characterization of the topology and defect distribution of the amorphous network is presented and discussed. The electronic structure of our sample is calculated as well. Finally, we discuss the reliability and transferability of the present computational scheme for large-scale simulations of compound semiconductor materials by comparing our results to first-principles calculations. INTRODUCTION
Up to now the only reliable computer simulations at finite-temperature of III-V compounds have been obtained by first-principles molecular dynamics (MD) methods. In particular, careful investigations have been carried out on-liquid (1) and amorphous (a) GaAs obtaining a good agreement with available experimental data. 1,2 More recently, a novel semi-empirical simulation scheme has been introduced, 3,4 where the forces governing the atomic motion are derived from the electronic structure of the sample as obtained by a semi-empirical tight-binding (TB) Hamiltonian. Such a TB molecular dynamics (TBMD) scheme has been successfully applied to both elemental5-7 and compound materials8 ,9 showing that it has both a large transferability and the required accuracy to describe complex semicondutor materials. On the other hand, the computational workload of TBMD is that one typical of a parametrized calculation and, consequently, large-scale simulations involving hundreds of atoms and/or long times (hundreds of picoseconds) are possible. In the present paper, we will apply TBMD to study the structural properties of a-GaAs. The choice of such a material is mainly motivated by its fundamental importance as paradigmatic case of amorphous binary semiconductor whose short-range-order (SRO) features are still matter of discussion. 2,10 In particular, two main issues must be clarified: a full characterization of the topological and chemical disorder of the amorphous network and the identification of structural point defects (like dangling or wrong bonds) due to the presence of threefold- and fivefoldcoordinated sites in the amorphous network We have already demonstrated 7 that the SRO feature of an amorphous semiconductor, as obtained in a computer experiment, are affected by the sample preparation. Consequently, one of the key points of the present work is the procedure adopted to prepare the a-GaAs sample. Taking full advantage from the relatively low computational cost of the TBMD code, we have been able to cool slowly a good sample of I-GaAs from 1600 K down to 300 K (at an average cooling rate of 2.7 1012 K/s, much slower than that one achievable in a first-principles simulation2). The resulting amorphous network has global structural properties matching in a 135 Mat. Res. Soc. S
Data Loading...
