Dielectric Response And Electric Properties Of Organic Semiconducting Phthalocyanine Thin Films

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Journal Title, Volume, Page: 
Journal of Semiconductors, Volume 33, Number 8
Year of Publication: 
A. M. Saleh
Physics Department, Al-Quds University, Jerusalem, Palestine
S. M. Hraibat
Physics Department, Al-Quds University, Jerusalem, Palestine
R. M-L. Kitaneh
Physics Department, Al-Quds University, Jerusalem, Palestine
M. M. Abu-Samreh
Physics Department, Al-Quds University, Jerusalem, Palestine
S. M. Musameh
Physics Department, An-Najah University, Nablus, Palestine
Preferred Abstract (Original): 
The dielectric function of some phthalocyanine compounds (ZnPc, H2Pc, CuPc, and FePc) were investigated by analyzing the measured capacitance and loss tangent data. The real part of the dielectric constant, ε1, varies strongly with frequency and temperature. The frequency dependence was expressed as: ε1 = Aωn, where the index, n, assumes negative values (n < 0). In addition, the imaginary part of the dielectric constant, ε2, is also frequency and temperature dependent. Data analysis confirmed that ε2 = Bωm with values of m less than zero. At low frequencies and all temperatures, a strong dependence is observed, while at higher frequencies, a moderate dependence is obvious especially for the Au-electrode sample. Qualitatively, the type of electrode material had little effect on the behavior of the dielectric constant but did affect its value. Analysis of the AC conductivity dependence on frequency at different temperatures indicated that the correlated barrier hopping (CBH) model is the most suitable mechanism for the AC conduction behavior. Maximum barrier height, W, has been estimated for ZnPc with different electrode materials (Au and Al), and had values between 0.10 and 0.9 eV For both electrode types, the maximum barrier height has strong frequency dependence at high frequency and low temperatures. The relaxation time, τ, for ZnPc and FePc films increases with decreasing frequency. The activation energy was derived from the slopes of τ versus 1/T curves. At low temperatures, an activation energy value of about 0.01 eV and 0.04 eV was estimated for ZnPc and FePc, respectively. The low values of activation energy suggest that the hopping of charge carriers between localized states is the dominant mechanism.
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