To measure the relative permittivity of a p-type semiconductor material (a metal phthalocyanine ) , a M-S-M structure was made by thermal evaporation method. The capacitance was measured by a LCR meter at room temperature under the frequency of 1 kHz and the thickness of semiconductor layer and active area of our sample were known .{ C=ε_r ε0 A/d }this equation was used to calculate the ε_r.
but the calculated value was lower than one! about 0.000035
I think that our LCR meter must be defective.
What do you think?
Relative dielectric constant can not be less than one. Either you are doing some mistake in calculation or your measurements are defective. You can check your LCR meter by measuring capacitance of a known value capacitor. Also check the conductance range of your meter. If your sample conductance is more than the conductance range of your meter, it may not give correct values for your sample even if the meter is O.K.
Relative dielectric constant can not be less than one. Either you are doing some mistake in calculation or your measurements are defective. You can check your LCR meter by measuring capacitance of a known value capacitor. Also check the conductance range of your meter. If your sample conductance is more than the conductance range of your meter, it may not give correct values for your sample even if the meter is O.K.
I agree with Dr. Kumar
What is the measured C value that you substituted in the equation?
Was it measured at Vg=0 ?
How were A and d measured?
What does an I-V curve of this structure look like?
absolutely agree with Dr. A. Kumar , it can't be less than 1, definitely there is some calculation mistake...
In addition to the previous comments, the frequency is very low. Either you try something like 100 kHz and more or try to do a frequency sweep. It should give you an indication if your LCR meter is capable of measuring at 1 kHz.
thanks for your good answers
the sample fabricated like a parallel plate capacitor and we know the active aria.
the thickness of evaporated MPc layer was determined using thickness monitor.
my calculation is true and i check it several times.
in this word AL was used as electrode, this metal and MPcs have Schottky contact
i used 1 kHz frequency because i read this method in some papers like
Effect of γ-rays on the optical and electrical properties of copper-phthalocyanine thick films...10.1109/MIEL.2002.1003209
Electrical properties of hybrid phthalocyanines thin films using
gold and lead electrodes...10.1140/epjb/e2005-00352-7
Electrical and optical properties of vacuum deposited MnPc
thin films...10.1140/epjb/e2005-00317-x
Influence of oxygen and post deposition annealing on the electrical properties of MnPc and MnPcCl Schottky barrier devices...http://link.springer.com/article/10.1007%2Fs10853-005-6926-0
Dear Prof. J.Grigas
thanks for your answer but as mentioned in these papers
Effect of γ-rays on the optical and electrical properties of copper-phthalocyanine thick films...10.1109/MIEL.2002.1003209
Electrical properties of hybrid phthalocyanines thin films using
gold and lead electrodes...10.1140/epjb/e2005-00352-7
Electrical and optical properties of vacuum deposited MnPc
thin films...10.1140/epjb/e2005-00317-x
Influence of oxygen and post deposition annealing on the electrical properties of MnPc and MnPcCl Schottky barrier devices...http://link.springer.com/article/10.1007%2Fs10853-005-6926-0
their measurements were done in 1KHz frequency
they have studied a kind of MPc material
I am curious about how do you know the depletion width of your device?
Do you mean the entire active area can be your depletion area?
In regions of strong dispersion the reletive dielectric constant may be smaller than one but only in a narrow frequency range (c.f. metamaterials).
However when doing meaurements at 1 Khz its much more likely that this is a measurement error ..there are MANY possibilities..but as said above...maybe the measurment method is not adequate and the material (film) is rather lossy...then anything can happen..or at least the test method should be crosschecked.
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