Diffusivity of the double negatively charged mono-vacancy in silicon

Area of Science:

• Materials Science
• Solid State Physics
• Semiconductor Physics

Background:

• Understanding point defects in silicon is crucial for semiconductor device performance.
• Silicon vacancies (V) are mobile defects that can interact with impurities, affecting material properties.

Purpose of the Study:

• To investigate the migration of silicon vacancies (V) in n-type silicon.
• To characterize the formation and properties of vacancy-oxygen (VO) complexes.
• To quantitatively determine the diffusivity of the silicon vacancy in its double negative charge state (V^2-).

Main Methods:

• Irradiation of lightly-doped n-type silicon with 2.0 MeV He+ ions at 30 K.
• In situ characterization using Deep Level Transient Spectroscopy (DLTS).
• Isothermal annealing studies in the temperature range of 70-90 K.

Main Results:

• Silicon vacancy (V^2-) migration begins above ~70 K.
• V^2- trapping by interstitial oxygen (O_i) forms vacancy-oxygen (VO) centers, creating an acceptor level at ~0.17 eV below E_c.
• First-order kinetics for VO formation were observed, enabling quantitative determination of V^2- diffusivity.

Conclusions:

• The diffusivity of V^2- exhibits an activation energy of ~0.18 eV and a pre-exponential factor of ~[Formula: see text] cm² s^-1.
• The migration of V^2- appears to be a simple jump process without significant entropy effects.
• The energy level of the V^2- defect is likely deeper than ~0.19 eV below E_c.