Frequency and temperature dependence of the dielectric and AC electrical conductivity in (Ni/Au)/AlGaN/AlN/GaN heterostructures

The dielectric properties and AC electrical conductivity (σ_ac)of the (Ni/Au)/Al_0.22Ga_0.78N/AlN/GaN heterostructures, with and without the SiN_x passivation, have been investigated by capacitance-voltage and conductance-voltage measurements in the wide frequency (5kHz-5 MHz) and temperature (80-400 K) range. The experimental values of the dielectric constant (ε′), dielectric loss (ε′′), loss tangent (tanδ), σ_ac and the real and imaginary part of the electric modulus (M′ and M′′) were found to be a strong function of frequency and temperature. A decrease in the values of ε′ and ε′′ was observed, in which they both showed an increase in frequency and temperature. The values of M′ and M′′ increase with increasing frequency and temperature. The σ_ac increases with increasing frequency, while it decreases with increasing temperature. It can be concluded, therefore, that the interfacial polarization can occur more easily at low frequencies and temperatures with the number of interface states density located at the metal/semiconductor interface. It contributes to the ε′ and σ_ac.