Grown-in beryllium diffusion in indium gallium arsenide: An ab initio, continuum theory and kinetic Monte Carlo study

Abstract

A roadblock in utilizing InGaAs for scaled-down electronic devices is its anomalous dopant diffusion behavior; specifically, existing models are not able to explain available experimental data on beryllium diffusion consistently. In this paper, we propose a comprehensive model, taking selfinterstitial migration and Be interaction with Ga and In into account. Density functional theory (DFT) calculations are first used to calculate the energy parameters and charge states of possible diffusion mechanisms. Based on the DFT results, continuum modeling and kinetic Monte Carlo simulations are then performed. The model is able to reproduce experimental Be concentration profiles. Our results suggest that the Frank-Turnbull mechanism is not likely, instead, kick-out reactions are the dominant mechanism. Due to a large reaction energy difference, the Ga interstitial and the In interstitial play different roles in the kick-out reactions, contrary to what is usually assumed. The DFT calculations also suggest that the influence of As on Be diffusion may not be negligible.arXiv:1608.00779v2 [cond-mat.mtrl-sci]

On the Charge State of Titanium in Titanium Dioxide

“…In many instances, there is a clear justification of such an assignment, based for example on the analysis of the band structure. 25,54 In the case of TiO 2 however, there is no solid justification for assigning e.g. the Bader charge of about +2.5 e to an oxidation state Ti 4+ .…”

Dopant–dopant interactions in beryllium doped indium gallium arsenide: An ab initio study

“…This is in spite of a well-known propensity of interstitial alkali earth atoms to donate both their valence electrons to Page 5 of 27 the conduction band of the semiconductor host [ 10,11,13,35 ]; the donation of two electrons to the conduction band was also explicitly computed for interstitial Be in InGaAs in Ref. [ 8 ]. In Ref.…”

“…[ 8 ], we proposed an ab initio approach to charge states whereby DFT is used to compute the charge states at 0 K (on a neutral cell, in agreement with the fact that bulk material is neutral), and electronic structure analysis is used to identify defect-centred states which could potentially be occupied at finite temperature, giving rise to a temperature-dependent distribution of charge states. Such ab initio derived charges were validated in continuous and Kinetic Monte Carlo models of Be diffusion which allowed to reproduce experimental diffusion profiles over a range of temperatures [ 8 ]. Here, we also use this approach.…”

“…We tested the effect of randomness in Ref. [ 8 ] and found that they were small; specifically, no significant changes in the band structure are caused by randomness and changes in reaction energies were small when exchanging the positions of In and Ga. Below we also show that In and Ga substitutional defects on Ga and In, respectively, have defect formation energies relatively close to zero and do not perceptibly modify the density of states (contrary to single or double defects involving interstitials considered below). Therefore the conclusions are not expected to be affected by the randomness of the alloys, although a detailed study of these effects is still outstanding but us not the subject of the present paper.…”

“…We now investigate interactions between those defects that are expected to play a role in Be diffusion, 8 as identified in the previous section based in particular on the defect formation energies. These include substitutional Be, In, and Ga as well as interstitial Be and Ga, which, although higher-energy then interstitial Be and Ga, can be significantly stabilized as shown below; Be interstitials are also expected to be involved in diffusion.…”