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Fig. 7. G/w-f graphs of Al/P3HT/p-Si (MPS) structure for various voltages in the frequency range of 3 kHz-1 MHz. Fig. 6. C-f graphs of Al/P3HT/p-Si (MPS) structure for various voltages in the frequency range of 3 kHz-1 MHz. When the C-V and G/w-V plots are obtained at sufficiently high frequency (f =1 MHz), the effect of surface states can be eliminated, since they do not follow ac signal above this frequency as mentioned before. In this case, the R, seems the most important parameter which causes the electrical characteristics of Schottky type structures to be non-ideal. To obtain the real capacitance and conductance, their values for high frequencies under forward and reverse bias were corrected as (C, and G,/a), for the effect of R, using the equations 7-9 [32].

Figure 7 G/w-f graphs of Al/P3HT/p-Si (MPS) structure for various voltages in the frequency range of 3 kHz-1 MHz. Fig. 6. C-f graphs of Al/P3HT/p-Si (MPS) structure for various voltages in the frequency range of 3 kHz-1 MHz. When the C-V and G/w-V plots are obtained at sufficiently high frequency (f =1 MHz), the effect of surface states can be eliminated, since they do not follow ac signal above this frequency as mentioned before. In this case, the R, seems the most important parameter which causes the electrical characteristics of Schottky type structures to be non-ideal. To obtain the real capacitance and conductance, their values for high frequencies under forward and reverse bias were corrected as (C, and G,/a), for the effect of R, using the equations 7-9 [32].

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Fig. 1. Schematic diagram of the Al/P3HT/p-Si (MPS) structure and measurement system. SOE AE ee eS eee eee ee eee ees Eee The C-V and G/w-V measurements of the Al/P3HT/p-Si (MPS) structure was performed in the frequency range of 3 kHz-1 MHz by using HP 4192 A LF impedance analyzer (5 Hz-13 MHz) and the test signal of 50 mV,.). All measurements were carried out at room temperature, with the help of a microcomputer through an IEEE-488 ac/dc converter card in the cryostat to avoid from any external noise.
Fig. 1. Schematic diagram of the Al/P3HT/p-Si (MPS) structure and measurement system. SOE AE ee eS eee eee ee eee ees Eee The C-V and G/w-V measurements of the Al/P3HT/p-Si (MPS) structure was performed in the frequency range of 3 kHz-1 MHz by using HP 4192 A LF impedance analyzer (5 Hz-13 MHz) and the test signal of 50 mV,.). All measurements were carried out at room temperature, with the help of a microcomputer through an IEEE-488 ac/dc converter card in the cryostat to avoid from any external noise.
of R, of the Al/P3HT/p-Si (MPS) structure. The reverse bias C* vs V plots of Al/P3HT/p-Si (MPS) structure were drawn for intermediate and high frequencies (f=3 kHz) at room temperature to extract the real values of some main electrical parameters such as Vp, Na, Ep and ®,. Since the contribution of the surface states to excess capacitance and conductance can be ignored, the measured valued of them is quite low at high frequencies. The C’-V plots exhibit a straight line in a wide bias range, and diffusion potential has been found from the extrapolation of this line to the voltage axis (V=0). For the purpose of getting structure paremeter, the reverse bias C’-V plot was drawn and given in Fig.4. From the slope of this line, one can calculate the different parameters such as Vp, Na, Em, Ep and ®g [36-40]. The found parameters could be seen in Table 1. As shown in Table 1, the obtained Vp, ®g Ep values increase with the increasing frequencies. It has been observed that the voltage axis extrapolation have changed from the reverse bias to forward bias by increasing frequency. For a MS, MIS and MPS type structure, the relationship between C and V in the depletion layer capacitance can be expressed as [31];
of R, of the Al/P3HT/p-Si (MPS) structure. The reverse bias C* vs V plots of Al/P3HT/p-Si (MPS) structure were drawn for intermediate and high frequencies (f=3 kHz) at room temperature to extract the real values of some main electrical parameters such as Vp, Na, Ep and ®,. Since the contribution of the surface states to excess capacitance and conductance can be ignored, the measured valued of them is quite low at high frequencies. The C’-V plots exhibit a straight line in a wide bias range, and diffusion potential has been found from the extrapolation of this line to the voltage axis (V=0). For the purpose of getting structure paremeter, the reverse bias C’-V plot was drawn and given in Fig.4. From the slope of this line, one can calculate the different parameters such as Vp, Na, Em, Ep and ®g [36-40]. The found parameters could be seen in Table 1. As shown in Table 1, the obtained Vp, ®g Ep values increase with the increasing frequencies. It has been observed that the voltage axis extrapolation have changed from the reverse bias to forward bias by increasing frequency. For a MS, MIS and MPS type structure, the relationship between C and V in the depletion layer capacitance can be expressed as [31];
Fig. 3. G/w-V plots of the Al/P3HT/p-Si (MPS) structure in the frequency range of 3 kHz-1 MHz. Fig. 2. C-V plots of the Al/P3HT/p-Si (MPS) structure in the frequency range of 3 kHz-1 MHz.
Fig. 3. G/w-V plots of the Al/P3HT/p-Si (MPS) structure in the frequency range of 3 kHz-1 MHz. Fig. 2. C-V plots of the Al/P3HT/p-Si (MPS) structure in the frequency range of 3 kHz-1 MHz.
Fig. 5. D,- In(f) plot of Al/P3HT/p-Si (MPS) structure in the frequency range of 3 kHz-1 MHz. Fig. 4. C*-V plots of Al/P3HT/p-Si (MPS) structure in the frequency range of 3 kHz-1 MHz. where Ny is the effective density of states in Si valance band, the effective mass of holes m*;,= 0.55mo [32] and m, is the rest mass of the electron. As to the changes in the Op it was given in Fig.5. As it is seen, the frequency dependent value of BH (®g(C—V)) increases with increasing frequency. This expected behavior of ® ,(C-V) is attributed to particular density distribution of N,, and the interfacial layer [33, 35]. At the same time, the decrease in C with increasing frequency depends not only on the decrease in N,, but also on the increase in Wp. As can be noted in Table | the values of Vp. Na, Ep, ®g(C-V) and Wp for the MPS capacitor increase with increasing frequency, whereas the value of Na decreases due to the surface states and relaxation time.
Fig. 5. D,- In(f) plot of Al/P3HT/p-Si (MPS) structure in the frequency range of 3 kHz-1 MHz. Fig. 4. C*-V plots of Al/P3HT/p-Si (MPS) structure in the frequency range of 3 kHz-1 MHz. where Ny is the effective density of states in Si valance band, the effective mass of holes m*;,= 0.55mo [32] and m, is the rest mass of the electron. As to the changes in the Op it was given in Fig.5. As it is seen, the frequency dependent value of BH (®g(C—V)) increases with increasing frequency. This expected behavior of ® ,(C-V) is attributed to particular density distribution of N,, and the interfacial layer [33, 35]. At the same time, the decrease in C with increasing frequency depends not only on the decrease in N,, but also on the increase in Wp. As can be noted in Table | the values of Vp. Na, Ep, ®g(C-V) and Wp for the MPS capacitor increase with increasing frequency, whereas the value of Na decreases due to the surface states and relaxation time.
Fig. 8 (a) The corrected C-V and (b) the corrected G/w-V plots of the Al/P3HT/p-Si (MPS) structure for 1 MHz and room temperature. where G, is the corrected conductance. As can be seen in Fig. 8(a), the values of corrected capacitance, C,, increase compared to the measured value o capacitance for 1 MHz especially in the depletion and accumulation regions. On the other hand, the values o corrected conductance, G,/@ decrease compared to providing that the charge transfer can take place through that be affected by R,, particularly at higher frequencies, structures and in the techniques used in measurements. inter polarization mechanism. Also, it can be attributed to traps localized at M/S interface. However, we observed cons ant at high voltages. he value of measured conductance as seen in Fig. 8(b), it is he interface. From the measured data, we also observed he values of corrected capacitance change with frequency. It is clear that both the C and G/o measurements can herefore a care should be exercised both in the preparation o This change in C, means that the dielectric constant of facial layer at M/S interfaces, whether native or deposited, changes with measured frequency because of the he trap charges which have enough energy to escape from the hat the values of corrected conductance remain almos
Fig. 8 (a) The corrected C-V and (b) the corrected G/w-V plots of the Al/P3HT/p-Si (MPS) structure for 1 MHz and room temperature. where G, is the corrected conductance. As can be seen in Fig. 8(a), the values of corrected capacitance, C,, increase compared to the measured value o capacitance for 1 MHz especially in the depletion and accumulation regions. On the other hand, the values o corrected conductance, G,/@ decrease compared to providing that the charge transfer can take place through that be affected by R,, particularly at higher frequencies, structures and in the techniques used in measurements. inter polarization mechanism. Also, it can be attributed to traps localized at M/S interface. However, we observed cons ant at high voltages. he value of measured conductance as seen in Fig. 8(b), it is he interface. From the measured data, we also observed he values of corrected capacitance change with frequency. It is clear that both the C and G/o measurements can herefore a care should be exercised both in the preparation o This change in C, means that the dielectric constant of facial layer at M/S interfaces, whether native or deposited, changes with measured frequency because of the he trap charges which have enough energy to escape from the hat the values of corrected conductance remain almos
Fig. 10. Nss-In(f) plots of the Al/P3HT/p-Si (MPS) structure in the wide frequency range of 3 kHz-1 MHz. Fig. 9. R,-V plots of the Al/P3HT/p-Si MPS type structure in the frequency range of 3 kHz-1 MHz. region correspond to R, values. As can be seen in Fig. 9, the change in R, becomes rather important in the depletion and accumulation regions, but nearly independent of the frequency in the strong inversion and depletion regions. This variation of R, with the frequency can be attributed to the the existence of N,, at P3HT/p-Si interface, interfacial layer, surface and dipole polarization. We believe that the traped charges at surface states or interface traps can easily follow the external ac signal especially at low frequencies. In general, the source of R, could be due to the non-ohmic back contact, leakage paths at interfacial layer/back contact interface, the contact made by the probe wire to the gate, the resistance of the bulk semiconductor, an extremely non-homogeneity of doping concentrations atoms distribution in the semiconductor and interfacial layer. The C-V measurements of the MS, MIS and MPS type structures confirmed the effect of the R,, N,, and interfacial layer which can be considered as a layer structures with nonlinear resistance, N,, and capacitance. Also, it is well known that the density of N,, is a useful guide for the quality of semiconductor devices such as SBDs. There are several methods to determine N,, [17, 22]. Among them, Hill-Coleman method [41] is important in terms of being fast and reliable. According to this method, the density of surface states can be expressed as
Fig. 10. Nss-In(f) plots of the Al/P3HT/p-Si (MPS) structure in the wide frequency range of 3 kHz-1 MHz. Fig. 9. R,-V plots of the Al/P3HT/p-Si MPS type structure in the frequency range of 3 kHz-1 MHz. region correspond to R, values. As can be seen in Fig. 9, the change in R, becomes rather important in the depletion and accumulation regions, but nearly independent of the frequency in the strong inversion and depletion regions. This variation of R, with the frequency can be attributed to the the existence of N,, at P3HT/p-Si interface, interfacial layer, surface and dipole polarization. We believe that the traped charges at surface states or interface traps can easily follow the external ac signal especially at low frequencies. In general, the source of R, could be due to the non-ohmic back contact, leakage paths at interfacial layer/back contact interface, the contact made by the probe wire to the gate, the resistance of the bulk semiconductor, an extremely non-homogeneity of doping concentrations atoms distribution in the semiconductor and interfacial layer. The C-V measurements of the MS, MIS and MPS type structures confirmed the effect of the R,, N,, and interfacial layer which can be considered as a layer structures with nonlinear resistance, N,, and capacitance. Also, it is well known that the density of N,, is a useful guide for the quality of semiconductor devices such as SBDs. There are several methods to determine N,, [17, 22]. Among them, Hill-Coleman method [41] is important in terms of being fast and reliable. According to this method, the density of surface states can be expressed as
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