Studies on capacitive, conductance and interface properties of silicon and silicon carbide mos structures

Abstract

Study on Conductance and Capacitance of Oxide Layers on Silicon and Silicon Carbide Through measurements on dc and ac conductance and incremental capacitance of oxide layers on silicon (n-type) and silicon carbide (n- and p-types), the following information has been obtained:

(i) Conduction Mechanism

The mechanism of conduction is probably of the Poole–Frenkel type, with activation energies of:

0.05 eV for oxides on silicon 0.08 eV for oxides on silicon carbide

An additional activation energy of about 0.95 eV for silicon substrates, applicable to some branches of the I–V curve, has also been observed and related to the bandgap of silicon.

(ii) Interface State Densities

Interface state densities observed:

~10¹? /m² for wet oxides in silicon MOS structures ~10¹² /m² for dry oxides in silicon MOS structures ~10¹¹ to 10¹² /m² in SiC MOS structures

Their distribution in the bandgap has been obtained. Temperature variation studies show:

Increase in interface state density with temperature for n-type Si and SiC MOS structures Decrease with temperature for p-type SiC MOS structures

(iii) Interface Recombination and Capture Cross Section

Interface recombination velocities: 10³ to 10? m/sec Interface state capture cross sections: 10?¹? to 10?¹? m² Temperature variations of recombination velocity and capture cross section have been studied. Capture cross sections:

Approximately constant in the depletion region Decrease steeply by two orders of magnitude toward accumulation in Si–SiO? and SiC–SiO? systems

Capture is probably of holes by neutral centers:

Practically no temperature variation in Si MOS samples Temperature variation observed in SiC MOS samples

The sharp drop toward accumulation and temperature dependence do not support conventional recombination mechanisms.

Additional Observations

Collateral measurements of I–V and C–V characteristics helped establish:

The role of interface state charges Bilateral conduction in Si and SiC MOS structures Occurrence of S-type switching accompanied by negative resistance in silicon carbide