Defect Engineering Strategies Research Articles

Tin diffusion in germanium: a thermodynamic approach

Point defect properties including diffusion properties are technologically important in semiconductor materials particularly as the characteristic dimension of devices are a few nanometers. Tin is an isovalent dopant in germanium that is presently considered to form radiation tolerant devices and in defect engineering strategies aiming to contain the high n-type dopant diffusion. In the present investigation we show that the cBΩ thermodynamic model linking the defect Gibbs energy to the isothermal bulk modulus and the mean volume per atom, can describe tin diffusion in germanium. The model is used to calculate point defect thermodynamic parameters such as the activation entropy, activation enthalpy and activation volume of tin diffusion in germanium as a function of temperature.

An atomistic vision of the Mass Action Law: Prediction of carbon/oxygen defects in silicon

We introduce an atomistic description of the kinetic Mass Action Law to predict concentrations of defects and complexes. We demonstrate in this paper that this approach accurately predicts carbon/oxygen related defect concentrations in silicon upon annealing. The model requires binding and migration energies of the impurities and complexes, here obtained from density functional theory (DFT) calculations. Vacancy-oxygen complex kinetics are studied as a model system during both isochronal and isothermal annealing. Results are in good agreement with experimental data, confirming the success of the methodology. More importantly, it gives access to the sequence of chain reactions by which oxygen and carbon related complexes are created in silicon. Beside the case of silicon, the understanding of such intricate reactions is a key to develop point defect engineering strategies to control defects and thus semiconductors properties.

Enhanced Electrical and Nuclear Radiation Detection Performance in BiI3 Wide Bandgap Semiconductor Detectors

BiI3 is a wide band-gap compound semiconductor with a high effective atomic number that is anticipated to exhibit higher detection efficiency than other compound semiconductors such as HgI2, PbI2, and CdZnTe. This makes BiI3 of particular interest for moderate and high energy gamma-ray detection applications. However, the low resistivity of BiI3 results in high leakage currents and degrades the electrical properties and detecting performance of the detectors. Here we show that the main reason for the low resistivity in BiI3 is due to the high volatility of iodine and the high concentration of intrinsic Schottky defects. Furthermore, we will discuss novel defect engineering strategies that successfully mitigate the obstacles associated with iodine vacancies in the material. Density functional theory (DFT) calculations, as well as experimentally measured electrical properties, and radiation response will be presented for undoped and Sb-doped BiI3 (SBI) single crystals grown via the vertical Bridgman growth technique. Most importantly, we will demonstrate the first ever recorded gamma-ray spectrum using BiI3-based detectors.

Diffusion ofn-type dopants in germanium

Germanium is being actively considered by the semiconductor community as a mainstream material for nanoelectronic applications. Germanium has advantageous materials properties; however, its dopant-defect interactions are less understood as compared to the mainstream material, silicon. The understanding of self- and dopant diffusion is essential to form well defined doped regions. Although p-type dopants such as boron exhibit limited diffusion, n-type dopants such as phosphorous, arsenic, and antimony diffuse quickly via vacancy-mediated diffusion mechanisms. In the present review, we mainly focus on the impact of intrinsic defects on the diffusion mechanisms of donor atoms and point defect engineering strategies to restrain donor atom diffusion and to enhance their electrical activation.

Strategies to suppress A-center formation in silicon and germanium from a mass action analysis viewpoint

We investigate the impact of tin (Sn) doping on the formation and the thermal stability of the vacancy-oxygen (VO or A-center) in the electron-irradiated Czochralski silicon (Si) and its conversion to the VO2 defects. Previous experimental studies are consistent with the viewpoint that Sn (and other oversized isovalent atoms) doping suppresses the formation of the A-center. The results are discussed in view of recent density functional theory calculations, whereas we employ mass action analysis to calculate the impact of isovalent dopants on the suppression of the A-center. We propose point defect engineering strategies to suppress the concentration of the deleterious A-centers in Si and in related materials such as germanium.

Defect engineering in germanium

State of the art nanoelectronic devices are mainly fabricated on silicon (Si). In order to take advantage of the properties of germanium (Ge) in advanced electronic nanodevices all steps of device fabrication must be controlled. This, in particular, concerns the diffusion, doping, and activation of dopants in Ge. In this paper, the mechanism of self‐ and dopant diffusion in Ge under thermal equilibrium and non‐equilibrium conditions are reviewed. Non‐equilibrium conditions can, e.g., be realized by irradiation, implantation, and the dissolution of unstable defect clusters. Defect reactions mediating dopant diffusion and dopant deactivation in Ge under different experimental conditions are discussed. Special attention is paid to the charge states of the involved point defects and their Coulomb interactions that explain numerous results on dopant diffusion and dopant deactivation. Controlling the formation of vacancies V and self‐interstitials I is the key to develop successful defect engineering strategies that are required to achieve the objectives for the fabrication of Ge‐based devices.

Defect engineering strategies for germanium

After years of neglect germanium is emerging as a mainstream material for microelectronics applications. This is partially due to the introduction of high-k dielectrics that have allowed the substitution of native oxides. Nevertheless, there are still difficulties concerning the fast diffusion and deactivation of n-type dopants. The aim of this review is to show how density functional theory (DFT) calculations can aid to the understanding of dopant-defect interactions and the design of defect engineering strategies to optimize the properties of doped germanium.

Point defect engineering strategies to retard phosphorous diffusion in germanium

The diffusion of phosphorous in germanium is very fast, requiring point defect engineering strategies to retard it in support of technological application. Density functional theory corroborated with hybrid density functional calculations are used to investigate the influence of the isovalent codopants tin and hafnium in the migration of phosphorous via the vacancy-mediated diffusion process. The migration energy barriers for phosphorous are increased significantly in the presence of oversized isovalent codopants. Therefore, it is proposed that tin and in particular hafnium codoping are efficient point defect engineering strategies to retard phosphorous migration.

Impact of isovalent defect engineering strategies on carbon-related clusters in silicon

In electron-irradiated silicon (Si) the formation of oxygen-vacancy pairs (VO or A-centers) is deleterious and for this reason isovalent defect engineering strategies have been proposed to suppress their concentration. Carbon-related clusters such as CiOi and CiCs are also important as they are electrically active and their properties need to be determined. The present study has two aims. The first aim is to review the impact of isovalent doping [germanium (Ge), tin (Sn) and lead (Pb)] on the thermal stability of the CiOi and CiCs pairs in Si by means of infrared (IR) spectroscopy. The second aim is to analyze these results and show that the presence of isovalent dopants in Si reduces the temperature of annealing (Tann) of the CiOi pairs and increases the temperature of annealing of the CiCs pairs. The results are discussed in view of recent experimental and theoretical studies. It is suggested that the change in the thermal stability of the C-related defects is due to the local strains induced in the lattice by the oversized isovalent dopants. It is surmised that these strains have an opposite impact on the Tann of the CiOi and CiCs pairs as a result of their different structures.

Point defect engineering strategies to suppress A-center formation in silicon

We investigate the impact of tin doping on the formation of vacancy-oxygen pairs (VO or A-centers) and their conversion to VO2 clusters in electron-irradiated silicon. The experimental results are consistent with previous reports that Sn doping suppresses the formation of the A-center. We introduce a model to account for the observed differences under both Sn-poor and Sn-rich doping conditions. Using density functional theory calculations, we propose point defect engineering strategies to reduce the concentration of the deleterious A-centers in silicon. We predict that doping with lead, zirconium, or hafnium will lead to the suppression of the A-centers.

Screw Dislocation-Driven Epitaxial Solution Growth of ZnO Nanowires Seeded by Dislocations in GaN Substrates

In the current examples of dislocation-driven nanowire growth, the screw dislocations that propagate one-dimensional growth originate from spontaneously formed highly defective "seed" crystals. Here we intentionally utilize screw dislocations from defect-rich gallium nitride (GaN) thin films to propagate dislocation-driven growth, demonstrating epitaxial growth of zinc oxide (ZnO) nanowires directly from aqueous solution. Atomic force microscopy confirms screw dislocations are present on the native GaN surface and ZnO nanowires grow directly from dislocation etch pits of heavily etched GaN surfaces. Furthermore, transmission electron microscopy confirms the existence of axial dislocations. Eshelby twist in the resulting ZnO nanowires was confirmed using bright-/dark-field imaging and twist contour analysis. These results further confirm the connection between dislocation source and nanowire growth. This may eventually lead to defect engineering strategies for rationally designed catalyst-free dislocation-driven nanowire growth for specific applications.

First-principles study of defects and carrier compensation in semiconductor radiation detector materials

AbstractWe discuss defect engineering strategies in radiation detector materials. The goal is to increase resistivity by defect-induced Fermi level pinning without causing defect-induced reductions in the carrier drifting length. We show calculated properties of various intrinsic defects and impurities in CdTe. We suggest that the defect complex of a hydrogen atom and an isovalent impurity on an anion site may be an excellent candidate in many semiconductors for Fermi level pinning without carrier trapping.