Mott-Schottky Analysis

Figure 1.41 Defect state concentration No determined by Schottky-Mott analysis of capacitance curves and corresponding Nb oxide stoichiometry as a function of the formation potential...

The Relaxation Spectrum Analysis was carried out for a cell consisting of n-CdSe in a liquid junction configuration with NaOH/S=/S 1 1 1M as the electrolyte. Three parallel RC elements were identified for the equivalent circuit of this cell, and the fastest relaxing capacitive element obeys the Mott-Schottky relation. 

As an example, for SCATD 1021 cm 3 and lOpFcm-2, the intercept according to the above analysis is shifted by ca. 70 mV. As Uosaki and Kita show by direct numerical calculation [67], for extreme values of exNd the Mott-Schottky plots are actually curved near flat-band. 

At present there is no unambiguous method for determining the energetic position of the conduction band edge of nanocrystalline semiconductor films under experimental conditions relevant to dye sensitization. Clearly, the lack of a depletion layer precludes traditional capacitance measurements with Mott-Schottky analysis described in Section 1.1. The onset of photocurrents in photocurrent-voltage plots can provide a crude working estimate under some conditions, but is problematic for the reasons described previously. This is unfortunate as accurate energetics are necessary to compare experimental results with even the simplest theory [4[. 

M-S Mott-Schottky analysis An electrochemical technique measuring... 

Of the techniques discussed in this chapter, impedance measurements are arguably the most complicated measurements to perform and interpret. The discussion below is limited to the most common form of impedance analysis used in solar water splitting research measuring a Mott-Schottky plot to determine the donor density... 

Van de Krol, R., Goossens, A., Schoonman, J. Mott-Schottky analysis of nanometer-scale thin-fihn anatase Ti02. J. Electrochem. Soc. 144, 1723-1727 (1997)... 

Erne et al. [240] have recently shown that the potential dependence of the DA under the depletion conditions is similar to the Mott-Schottky line, which allows determination of the flat-band potential of the electrode. Other examples of employing DA in spectroelectrochemical studies are analysis of the relaxation process of free carriers in semiconductor electrodes [241] and elucidating the mechanisms of interfacial processes (Section 7.5). 

An interpretation of the potential dependent capacitance (Mott-Schottky analysis [14]) yields information about semiconducting properties of the electrode. The corresponding experiment requires a modified technique in non-stationary systems, because the complete function must be measured in extremely short times to avoid fundamental system changes. This was done by superimposing small pulse to each step of a potential staircase (Fig. 6). With this technique, the complete analysis requires less than 500 ps [15]. 

Pulse and Step Methods, Fig. 6 Example of pulse measurements of the potential dependent capacitance for Mott-Schottky analysis. The electrode was pre-polarized toE ... 

Combining (20) and (21) leads to a dependence of capacitance on the square root of the concentration of charged defects. To be able to determine the defect concentration by fitting a straight line to the data, the Mott-Schottky analysis involves the plot of C vs applied d.c. voltage. The intersect of C with the voltage axis yields... 

Obviously this analysis is only possible if the width of the space charge regirai is much smaller than the device thickness. The consequences of using the Mott-Schottky analysis in insufficiently thick devices are discussed in one of the case studies in Sect. 4.4. 

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