First-principles survey of the structure, formation energies, and transition levels of As-interstitial defects in InGaAs

Abstract

While point defects in elemental (Si) and compound (GaAs, GaN, AlN) semiconductors have been extensively studied both experimentally and theoretically, only limited theoretical studies of these defects exist for technologically important binary (Si x Ge 1-x ) and pseudo-binary (In x Ga 1-x As, In x Ga 1-x N, Al x Ga 1-x N) semiconductor alloys. Here, we use density-functional theory (DFT) and a recently developed boundsanalysis approach to survey the atomic structures, formation energies, and charge-state transition levels of the stable and metastable states of As interstitials in the pseudo-binary alloy In 0.5 Ga 0.5 As. Our studies consider seven different candidate defect structures for the As interstitial, with calculations performed for selected defect charge states in the range q=-2 to q=+3. In each case, the mean and standard deviation of the defect formation energy are determined using statistical sampling methods that place the defect into a wide variety of differing local-alloy environments. When examined from the point of view of the mean formation energy of the defect, the stable configurations of the As interstitial in In 0.5 Ga 0.5 As are found to resemble previous findings for GaAs, with a C 1h -p001 III interstitial structure in a q=+1 charge state favored near mid-gap and below, and a C 2v -110 a split-interstitial structure in a q=-1 charge state favored above mid-gap (the named point-group symmetries refer to the underlying symmetry that the alloy defect would possess if within GaAs). The statistical sampling reveals a strong dependence of the defect formation energy on the local alloy environment, with the standard deviation, σ, of the formation energy approaching 0.21 eV for the most stable As-interstitial structures. Because the range of ground-state 2 energies encountered by an As interstitial defect when moving through the alloy is found to be quite large, approaching ~ 1.2 eV (±3σ), defect-diffusion pathways in In 0.5 Ga 0.5 As will have spatial and temporal complexities not found in GaAs. ________________________ a) Electronic mail: srlee@sandia.gov 3

Native Defects and Their Doping Response in the Lithium Solid Electrolyte Li7La3Zr2O12

“…In addition, in a system with inherent lithium disorder, the energy change (formally enthalpy change) upon adding or removing a lithium ion is no longer given by the energy difference between a single host and defect configurations (as in eq ). Instead, the energies of the host and defective systems should be computed as ensemble averages over all thermally accessible microstates. ,, The development of quantitatively accurate models of defect equilibria in inherently disordered solid lithium-ion electrolytes is therefore expected to require advances in both the thermodynamic formalism used in constructing models and in the computational approaches used for calculating defect energies. Meeting these goals, however, brings the promise of a more precise understanding of defect chemistry of a broad range of solid electrolytes, and the potential for more accurate and practical tuning of their material properties through doping and controlled synthetic conditions.…”

CoFFEE: Corrections For Formation Energy and Eigenvalues for charged defect simulations

“…Point defects, ubiquitous in materials, influence their electrical and optical properties. First principles electronic structure calculations have proven to be vital in understanding and predicting the role of defects [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]. Defect engineering to enhance or suppress certain characteristics of materials often rely on such simulations for inputs [19,20,21,22,23,24,25].…”

N-type Doping Strategies for InGaAs

“…Other recent DFT studies have been carried out to calculate the energetics of the possible diffusion mechanisms and defects in InGaAs [98,99]. Their work supports the trend that formation energies of cation vacancies V In V Ga , decreases with increasing Fermi level and that the formation energy of interstitial Si is much higher than that of substitutional silicon.…”