Toward Understanding Radiation Defects in a Ternary InGaAs Alloy

Ternary alloys such as InGaAs enable crucial functionalities in microelectronics and photonics, e.g. infrared photodetectors. Subjected to radiation, InGaAs devices are vulnerable to degradation attributed to displacement damage, point defects created by knocking atoms out of their lattice positions. While great progress has been documented in understanding radiation-induced defects in crystalline semiconductors (e.g. in Si or in binary III-V’s such as GaAs), this understanding is lacking in InGaAs, complicated by compositional disorder on the III{Ga,In} site. There is a dearth of defect-resolved data on one side, its interpretation hampered by lack of predictive theory—due to significant conceptual and computational challenges in modelling defects with random composition of In and Ga on the III-site—on the other. We use density functional theory (DFT) in a supercell approach to compute defect properties in InGaAs. We obtain defect energies and levels via comprehensive sampling from sites in a cubic 64-atom In(0.5)Ga(0.5)As special quasirandom structure (SQS) to computationally approximate the technologically relevant In(0.53)Ga(0.47)As lattice-matched to InP substrates. Invoking an equivalent-site principle, we define atom chemical potentials to obtain and verify site-consistent defect formation energies: e.g.. a III-site vacancy formation energy should be agnostic of the III-atom in the original SQS model. We use a hypercell approach—a 512-atom 2x2x2 supercell of 64-atom SQS supercells—to minimize cell-size errors. A LMCC (local-moment countercharge) eliminates jellium charge-errors and, incidentally, avoids the well-known band gap problem (DFT often severely underpredicts the band gap). Computed defect formation energies and defect levels in InGaAs, obtained as representative averages over all unique SQS sites, are intermediate in many respects between analogous defects in the binary end-members, GaAs and InAs, but with discriminating deviations that might be used in conjunction with experiments to identify and characterize radiation defects. This Rosetta Stone of defect properties is essential to interpret and also to guide radiation-defect experiments in InGaAs.
----- This work was supported, in part, by a Laboratory Directed Research and Development (LDRD) Project, (No. 233119). Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525.