Density Functional Modelling of Point Defects in Semiconductors Chris Ewels, PhD Thesis, July 1997

Models are proposed for three different types of shallow thermal donor in silicon, N_iO_2i, (CH)_iO_4i and Al_sO_4i. This includes a new mechanism for converting otherwise deep level defects into shallow donor level centres, through electrostatic compression via neighbouring oxygen atoms. A reconstruction mechanism is also found whereby (CH)_iO_4i can transform into a deep state defect.

Several thermal donor models are examined, and a centre consisting of a `di-y-lid', O_4i is shown to account for most of the observed experimental properties. Higher order thermal donor formation is discussed, as well as the role of hydrogen and silicon self-interstitials in thermal donor behaviour.

Rapid oxygen diffusion is examined in the context of the oxygen dimer, O_2i. A puckered dimer structure is shown to be stable with ¹⁶O modes in good agreement with experiment. A low energy migration path for dimer diffusion is determined. The role of the dimer in creating other oxygen-based point defects in silicon is discussed.

Oxygen complexes with nitrogen are also modelled, and the most common N/O defect is shown to be N_2iO_i, consisting of bond centred oxygen neighbouring an interstitial nitrogen square. A N_iO_i complex is also identified and correlated with experimental data. Various vacancy--oxygen complexes are studied and their anomalous formation discussed. The structure VO₂ is unambiguously assigned to experimental infra-red absorption at 889 cm^-1.

Finally the interaction between hydrogen, Group-II elements and vacancies in III-V materials is examined, particularly InP. VH₄ in InP is shown to be a single shallow donor, responsible for Fe charge compensation observed in InP:Fe-H. Trends in structure with varying Group-II element and III-V material are examined.

Available as:	HTML	PDF (1.6MB)	Postscript (2.95MB)
	Gzipped Postscript (0.77MB)	Gzipped tarred LaTeX (0.52MB)

---

Home

AIMPRO Thesis page

AIMPRO

TCCM