The investigation of frequency and voltage dependent electrical and dielectric properties of metal-insulator-semiconductor (Al/SiO2/p-Si) structures

In this study, in order to achieve a better understand of the effects of different charge interface states and their relaxation time and thickness of oxide layer (SiO2) on the electrical characteristics, we fabricated with thin (50 Å) and thicker (826 Å) metal-insulator-semiconductor (Al/SiO2/p-Si) structures and these structures are called sample A and sample B, respectively. The energy distribution profile of the interface states (Nss) and their relaxation time (?) and capture cross section (?p) of these structures have been investigated using admittance spectroscopy method (capacitance-voltage(C-V) and conductance-voltage (G/?-V)). The frequency dependent C-V and G/?-V characteristics of these devices were investigated by considering the series resistance (Rs) effects in a wide frequency range of 1 kHz-1 MHz at room temperature. The increase in capacitance especially at low frequencies results from the presence of interface states at Si/SiO2 interface. The values of Nss, ? and ?p changed from 9,55x1013 to 5,82x1013eV-1cm2, 6,31x10-6 to 1,58x10-6s, 3,55x10-21 to 1,27x10-15cm2, for sample A, 4,29x1013 to 3,36x1012 eV-1cm2,6,31x10-6to 1,58x10-6 s , 6,65x10-21 to 6,69x1015 cm2 for sample B. The values of Nss in sample A is almost one order higher than in those sample B. This indicates that the insulator layer at metal/semiconductor interface can passivate the surface states effectively. On the other hand, the frequency and voltage dependence of real and imaginary parts of dielectric constant (?' and ?'') and electric modulus (M' and M''), loss tangent (tan?) and ac electrical conductivity (?ac) of Al/SiO2/p-Si (MOS) structures have been investigated by admittance spectroscopy method in the frequency range of 1 kHz-1 MHz at room temperature. The values of ?', ?'', tan?, M', M'' and ?ac were found to be a strong function of frequency and applied bias voltage in the depletion region of capacitance (C) and conductance (G/?). The experimental results show that the interfacial polarization can more easily occur at low frequencies consequently contributing to the dispersion in ?', ?'', tan?, M', M' and ?ac values of MOS structure. The dispersion in the dielectric properties may be also attributed to a particular density distribution of interface states (Nss) at Si/SiO2 interface as well as space charge carriers and in-homogeneity of interfacial oxide layer. In addition, the value ac conductivity increase with increasing frequency can be attributed hopping type conduction mechanism.Key Words : Interface states; Relaxation time; Capture cross section; Admittance method; Insulator layer; Dielectric properties; Electric modulus; Conductivity.