Gallium interstitial contributions to diffusion in gallium arsenide

Joseph T Schick,Caroline G Morgan

doi:10.1063/1.3644937

Abstract

A new diffusion path is identified for gallium interstitials, which involves lower barriers than the barriers for previously identified diffusion paths [K. Levasseur-Smith and N. Mousseau, J. Appl. Phys. 103, 113502 (2008), P. A. Schultz and O. A. von Lilienfeld, Modelling and Simulation in Materials Science and Engineering 17, 084007 (2009)] for the charge states which dominate diffusion over most of the available range of Fermi energies. This path passes through the ⟨110⟩ gallium-gallium split interstitial configuration, and has a particularly low diffusion barrier of 0.35 eV for diffusion in the neutral charge state. As a part of this work, the character of the charge states for the gallium interstitials which are most important for diffusion is investigated, and it is shown that the last electron bound to the neutral interstitial occupies a shallow hydrogenic bound state composed of conduction band states for the hexagonal interstitial and both tetrahedral interstitials. How to properly account for the contributions of such interstitials is discussed for density-functional calculations with a k-point mesh not including the conduction band edge point. Diffusion barriers for gallium interstitials are calculated in all the charge states which can be important for a Fermi level anywhere in the gap, q = 0, +1, +2, and +3, for diffusion via the ⟨110⟩ gallium-gallium split interstitial configuration and via the hexagonal interstitial configuration. The lowest activation enthalpies over most of the available range of Fermi energies are found to correspond to diffusion in the neutral or singly positive state via the ⟨110⟩ gallium-gallium split interstitial configuration. It is shown that several different charge states and diffusion paths contribute significantly for Fermi levels within 0.2 eV above the valence band edge, which may help to explain some of the difficulties [H. Bracht and S. Brotzmann, Phys. Rev. B 71, 115216 (2005)] which have been encountered in fitting experimental results for heavily p-type, Ga-rich gallium arsenide by simply extending a model for gallium interstitial diffusion which has been used for less p-doped material.

Highlights

Gallium interstitial diffusion in gallium arsenide was proposed to be modeled well with doubly or triply positive charge states.[4]
A new diffusion path is identified for gallium interstitials, which involves lower barriers than the barriers for previously identified diffusion paths[1,2] for the charge states which dominate diffusion over most of the available range of Fermi energies.[13]. This path passes through the 110 gallium-gallium split interstitial configuration, and has a low diffusion barrier of 0.35 eV for diffusion in the neutral charge state
As a part of this work, the character of the charge states for the gallium interstitials which are most important for diffusion is investigated, and it is shown that the last electron bound to the neutral interstitial occupies a shallow hydrogenic bound state composed of conduction band states for the hexagonal interstitial and both tetrahedral interstitials

Summary

INTRODUCTION

Into gallium arsenide under arsenic-rich and arsenic-poor conditions,[7] and concluded that the doubly and triply positive charge states of gallium interstitials can adequately model the diffusion profiles.[6, 7]. Activation enthalpies for diffusion via these paths are presented as a function of Fermi level both for the case where interstitial concentrations are determined by thermal equilibrium, and for the case where there are high, non-equilibrum concentrations of interstitials, such as may occur in irradiated material. From these energetic studies a comprehensive picture of gallium diffusion across experimentally accessible conditions emerges

APPROACH

Defect energy and structure

Pathways for diffusion

Diffusion dependence on stoichiometry and doping

CONCLUSION