Surface state and surface recombination velocity characteristics of Si-SiO2interfaces

A new device has been used to study the surface recombination velocity and surface state characteristics of Si-SiO
2
interfaces. The device consists of an epitaxially-formed junction diode. When the junction is forward-biased, minority carriers are injected from the heavily-doped substrate into the lightly-doped epitaxial region. The thickness of the epitaxial region is much less than the diffusion length for minority carriers. Thus, the diode current for a given junction forward bias is directly proportional to surface recombination velocity at the Si-SioO
2
interface. A gate electrode over the SiO
2
has been included to vary surface potential. Thus, this new device permits one to simultaneously study MOS capacitance-voltage characteristics as well as surface recombination velocity. The capacitance-voltage characterics indicate the surface states exhibit a quasi-continuous energy distribution. N-type surfaces exhibited donor levels lying in the range of ∼0.15 to ∼0.45 eV above the valence band; their density was found to vary from ∼5 × 10
¹²
to 5 × 10
¹³
states/cm
²
/eV. In contrast, p-type surfaces exhibited acceptor levels lying in the range of ∼0.15 to ∼0.45 eV below the conduction band; their density was comparable to those observed on n-type surfaces. The maximum value of surface recombination velocity was found to vary from 3 × 10
³
to > 10
⁴
cm/s. Surface recombination velocity was found to correlate directly with surface state density.