Piotr Śpiewak

On the solubility and diffusivity of the intrinsic point defects in germanium

There is a strong interest to use germanium as an active device layer in deep sub-micron devices. This imposes similar stringent material and process requirements for germanium as for silicon. Lattice defect formation during crystal growth and device processing as well as dopant diffusion and activation are to a large extent controlled by the intrinsic point defects in the semiconductor. The properties of the vacancy and the self-interstitial in germanium are, however, not well known. The scarce available experimental data are combined with ab initio and molecular-dynamics calculations and other published simulation results. Based on this a best estimate is made for the formation and migration energies of the vacancy and the self-interstitial in germanium.

First principles calculations of the formation energy and deep levels associated with the neutral and charged vacancy in germanium

Density functional theory with local density approximation including on-site Coulomb interaction has been used to calculate the formation energy of the neutral and charged vacancy in germanium as a function of the Fermi level. The calculations suggest that vacancies in germanium are multiple-level acceptors with a first level at 0.02eV and a second level at 0.26eV above the valence band maximum in agreement with published experimental data. The formation energies of the neutral and charged vacancies line up well with the experimental values estimated from quenching experiments.

Improved calculation of vacancy properties in Ge using the Heyd-Scuseria-Ernzerhof range-separated hybrid functional

The revised Heyd-Scuseria-Ernzerhof screened hybrid functional (HSE06) is used for calculating the formation and migration energies of the vacancy in Ge, and the results are compared with those previously obtained using the local density approximation with the on-site Coulomb interaction U (LDA+U) approach and with other published results. It is demonstrated that using HSE06 gives a much more accurate electronic description of the vacancy and yields an excellent estimate of the activation energy of self-diffusion in Ge consistent with experimental data. The migration energies of the vacancy in different charge states calculated with the HSE06 approach agree well with the results of low-temperature infrared-absorption measurements. In contrast to previous results, the HSE06 calculations suggest that vacancies in Ge are multiple-level acceptors with levels located in the upper half of the bandgap. This can explain the observed high density of acceptor-like interface traps near the conduction band, pinning t...

Recent progress in understanding of lattice defects in Czochralski-grown germanium: catching-up with silicon

Recent progress is presented in the understanding of grown-in defects in Czochralskigrown germanium crystals with special emphasis on intrinsic point defects, on vacancy clustering and on interstitial oxygen. Whenever useful the results are compared with those obtained for silicon.

First Principles Calculations of the Formation Energy of the Neutral Vacancy in Germanium

Density functional theory (DFT) with local density approximation has been used to calculate the formation energy (EF) of the neutral vacancy in germanium single crystal. It was shown that careful checking of convergence with respect to the number of k-points is necessary when calculating the formation energy of the intrinsic point defects in Ge. The formation energy of the single neutral vacancy was estimated at 2.35 eV which is in excellent agreement with published experimental data.

Titanium-related color centers in diamond: a density functional theory prediction

Transition metal-related paramagnetic centers in diamond exhibiting bright photoluminescence are increasingly important defects for realizing high quality solid state single photon sources. Recently, advanced ab initio calculations of single nickel-related NE4 (nickel-vacancy) and NE8 (nickel-vacancy-nitrogen) complexes in nanodiamond provided an insight into the nature of optical transitions and demonstrated their potential for in vivo biomarker applications. For other transition metal-related defects in diamond, however, a comprehensive understanding of photoluminescence is rather scarce. Here we used first principles, hybrid density functional theory analysis to investigate the electronic structure and magneto-optical properties of titanium-related point defects in diamond. Our theoretical results including the paramagnetic S = 1/2 ground state, the calculated zero-phonon lines, quasi-local vibrational modes associated with Ti atoms, and hyperfine coupling parameters provide strong evidence that the neutral Ti–N and TiV–N complexes are indeed the experimentally observed N3 (titanium–nitrogen) and OK1 (titanium-vacancy–nitrogen) color centers. In addition, we predicted another low energy excitation in the spin minority channel of the TiV–N0 defect that needs further experimental verification and might be an interesting candidate for a robust solid state single color emitter in the near IR region. In the case of a yet unobserved, neutral TiV (titanium-vacancy) defect we found a high symmetry D3d configuration in the triplet 3Eu ground state and we calculated the magneto-optical parameters to mediate its future identification. We emphasize the possibility of the dynamic Jahn–Teller effect for some centers and its impact on the experimentally observed hyperfine structure.

Microdefects Modeling in Germanium Single Crystals

The knowledge of the dynamics of intrinsic point defects, is essential for controlling and engineering their formation and clustering and thus also the quality of the germanium crystals used for producing germanium wafers for space solar cells and terrestrial concentrator photovoltaic, as well as of the active layer of germanium in complementary metal-oxide semiconductors technology. The analyses presented in this paper relate technological process parameters with microdefect formation in single crystal germanium.