PhD Theses - Hassan Tahini
Controlling Dopant Distributions and Structures in Advanced Semiconductors
Dr. Tahini’s Google Scholar Profile
The suitability of silicon for micro and sub-micro electronic devices is being challenged by the aggressive and continuous downscaling of device feature size. New materials with superior qualities are continually sought-after. In this thesis, defects are examined in two sets of silicon alternate materials; germanium (Ge) and III-V semiconductors. Point defects are of crucial importance in understanding and controlling the properties of these electronic materials. Point defects usually introduce energy levels into the band gap, which influence the electronic performance of the material. They are also key in assisting mass transport.
Here, atomistic scale computational methods are employed to investigate the formation and migration of defects in Ge and III-V semiconductors. The behaviour of n-type dopants coupled to a vacancy in Ge (known as E-centres) is reported from thermodynamic and kinetic points of view, revealing that these species are highly mobile, consequently, a strategy is proposed to retard one of the n-dopants. Further, the electronic structure of Ge is examined and the changes induced in it due to the application of different types of strain along different planes and directions. The results obtained agree with established experimental values regarding the bands transition from indirect to direct under biaxial strain. This is used to support further predictions, which indicate that a moderate strain parallel to the  direction can efficiently transform Ge into a direct band gap material, with a band gap energy useful for technological applications.
Vacancies and antisites in III-V semiconductors have been studied under various growth and doping conditions. Results presented in this thesis help predict and explain the stability of some defects over a range of growth conditions. This, together with knowledge of the kinetics of migration of Ga and As/Sb vacancies is used to explain the disparities in self-diffusion between GaAs and GaSb.
Journal Articles Resulting from this Thesis
- H. A. Tahini, A. Chroneos, H. Bracht, S. T. Murphy, R. W. Grimes and U. Schwingenschlögl, “Antisites and anisotropic diffusion in GaAs and GaSb”, Applied Physics Letters, 103 (2013) 142107. doi:10.1063/1.4824126 PDF
- H. A. Tahini, A. Chroneos, S. T. Murphy, R. W. Grimes and U. Schwingenschlögl, “Vacancies and defect levels in III-V semiconductors” Journal of Applied Physics, 114 (2013) 063517. doi:10.1063/1.4818484 PDF
- H. A. Tahini, A. Chroneos, U. Schwingenschlögl and R. W. Grimes, “Co-doping with antimony to control phosphorous diffusion in germanium” Journal of Applied Physics, 113 (2013) 073704. doi:10.1063/1.4792480 PDF
- H. A. Tahini, A. Chroneos, R. W. Grimes and U. Schwingenschlögl, “Point defect engineering strategies to retard phosphorous diffusion in germanium”, Physical Chemistry Chemical Physics 15 (2013) 367. doi:10.1039/C2CP42973J
- H. A. Tahini, A. Chroneos, R. W. Grimes, U. Schwingenschlögl and A Dimoulas, “Strain induced changes to the electronic structure of germanium”, Journal of Physics: Condensed Matter, 24, (2012) 195802. doi:10.1088/0953–8984/24/19/195802
- H. A. Tahini, A. Chroneos, R. W. Grimes and U. Schwingenschlögl, “Diffusion of tin in germanium: a GGA+U approach”, Applied Physics Letters, 99 (2011) 162103. doi:10.1063/1.3653472 PDF
- H. A. Tahini, A. Chroneos, R. W. Grimes, U. Schwingenschlögl and H. Bracht, “Diffusion of E-Centres in germanium predicted using the GGA+U approach”, Applied Physics Letters, 99 (2011) 072112. doi:10.1063/1.3625939 PDF