arXiv subjects

Leopoldo Diaz

Publications and source records attributed to Leopoldo Diaz.

3 recordsLinked to original sources

arXiv2026

No band gap, no problem: Defects in InAs using a band-avoiding occupation-constrained density functional theory

Density functional theory (DFT) underestimates the experimental band gap---the infamous band gap problem. As the band gap defines the energy scale of defect levels, this complicates computation of charge transition energies for atomic defects. In the extreme case of narrow-gap semiconductors, the DFT band gap collapses to zero, seemingly precluding quantitative predictions of defect levels. We present a band-avoiding occupation-constrained DFT (ba-occ-DFT) approach that prevents spurious occupation of band-edge states and enables reliable total energy calculations of atomic defects. Application to indium arsenide (InAs) shows that ba-occ-DFT circumvents the band gap problem, separates band-edge errors from defect level calculations, and enables rigorous defect level predictions in a narrow-gap semiconductor despite a zero DFT band gap.

cond-mat.mtrl-sci↗

arXiv2025

An Atomistically Informed Device Engineering (AIDE) Method Realized: A case study in GaAs

Radiation-induced defects can have a significant impact on the longevity and performance of semiconductor devices. We present an Atomistically Informed Device Engineering (AIDE) method that integrates first-principles defect properties and experimentally measured parameters into a device model to dynamically simulate the defect chemistry in semiconductors. For a silicon-doped gallium arsenide (GaAs) material, we showcase three capabilities: (i) Fermi level $E_F$ movement including its component electron and hole Fermi levels, (ii) dynamical charge equilibration with the arsenic vacancy serving as an example, and a (iii) diffusion-driven reaction between Coulomb attracted gallium interstitial ($Ga_i$) and arsenic vacancy ($v_{As}$). Governed by charge carrier reactions, the electron and hole Fermi levels remained dissimilar until equilibrium was achieved at $E_F\approx1.32$ eV. The equilibrium Fermi level was verified by successfully identifying $v_{As}^{3-}$ as the most populated charge state within the arsenic vacancy defect. Lastly, a Coulomb attraction, created by the shifted Fermi level and the charge equilibration process, between $Ga_i^{1+}$ and $v_{As}^{3-}$ resulted in the formation of a doubly negative gallium antisite ($Ga_{As}^{2-}$). The AIDE method can access experimentally inaccessible short-time and low-concentration regimes, is generalizable to other more complex systems (e.g., indium gallium arsenide), and, after solving open problems in GaAs, will serve as a virtual experiment to bound estimates for difficult-to-measure physical quantities.

cond-mat.mtrl-sci↗

arXiv2025

The case of the missing gallium vacancy in gallium arsenide: A multiscale explanation

Irradiation of gallium arsenide (GaAs) produces immobile vacancies and mobile interstitials. However, after decades of experimental investigation, the immobile Ga vacancy eludes observation, raising the question: Where is the Ga vacancy? Static first-principles calculations predict a Ga vacancy should be readily observed. We find that short-time dynamical evolution of primary defects is key to explaining this conundrum. Introducing a multiscale Atomistically Informed Device Engineering (AIDE) method, we discover that during the initial displacement damage, the Fermi level shifts to mid-gap producing oppositely charged vacancies and interstitials. Driven by Coulomb attraction, fast As interstitials preferentially annihilate Ga vacancies, causing their population to plummet below detectable limits before being experimentally observed. This innovative model solves the mystery of the missing Ga vacancy and reveals the importance of a multiscale approach to explore the dynamical chemical behavior in experimentally inaccessible short-time regimes.

cond-mat.mtrl-sci↗