Admittance spectroscopy measurement

It must also be mentioned that evidence for USTDs with ionization energies down to 23 mcV has been obtained by low-temperature admittance spectroscopy and thermally-stimulated capacitance measurements in standard CZ silicon samples annealed at 470°C in oxygen ambient for up to 500 h [1],... 

In 677-SiC, B replaces a Si atom and its ionization energies in the three non-equivalent sites measured by admittance spectroscopy are 0.27, 0.31, and 0.38 eV [56], In undoped and boron-doped p-type 6H-SiC samples, a photoionization spectrum with a temperature-dependent threshold between 0.5 and 0.7eV, and a maximum at 1.75 eV has been reported [83]. The difference between the threshold energy and the electrically-measured ionization energy of B (0.3-0.4eV) is attributed to lattice relaxation. This photoionization spectrum is correlated with the observation near LHeT of three narrow absorption lines at 2.824, 2.863, and 2.890 eV tentatively attributed to excitons bound to neutral B at the three possible sites in 6H-SiC. 

In this Datareview, we concentrate on deep levels measured by capacitance and admittance techniques those measured by other techniques are detailed in Datareview 4.1. For completeness, trap parameters for major defects and impurities obtained from all techniques are listed. Capacitance techniques have proven useful for the characterisation of deep states in semiconductor devices. In particular, states which are non-radiative can be analysed by this technique. If the state under study is one which principally determines the conductivity of the crystal, the techniques of admittance spectroscopy are used. The set-up for doing capacitance and admittance spectroscopy on SiC is identical to that used for other semiconductors with the exception of the necessity to operate the system at higher temperatures in order to access potentially deeper levels in the energy gap. The data are summarised in TABLE 1. 

Photoluminescence (PL) and EL spectroscopy can be used to determine the presence of traps. Other techniques include current voltage measurements, capacitance voltage measurements, capacitance transient spectroscopy, and admittance spectroscopy. Under favorite conditions, the identification of the nature of the trap is possible. 

In most cases, the measurements are carried out isothermally in the frequency domain and the terms dielectric spectroscopy (DS) and dielectric relaxation spectroscopy (DRS) are then used. Other terms frequently used for DRS are impedance spectroscopy and admittance spectroscopy. Impedance spectroscopy is usually used in connection with electrolytes and electrochemical studies, whereas admittance spectroscopy often refers to semiconductors and devices. Isothermal measurements in the time domain are often used, either as a convenient tool for extending the range of measurements to low frequencies (slow time-domain spectroscopy, dc transient current method, isothermal charging-discharging current measurements) or for fast measurements corresponding to the frequency range of about 10 MHz - 10 GHz (time-domain spectroscopy or time-domain reflectometry). Finally, TSDC is a special dielectric technique in the temperature domain, which will be discussed in Section 2.2. 

Admittance measurements were used extensively prior to the widespread use of impedance spectroscopy in the 1980s. Capacitance bridge methods are typically used, though this limits the lower bound on the measured frequency to several hundred hertz. Corrosion processes, whose time constants are normally measured at or below 1 Hz, cannot be directly interrogated with this method. 

Immittance — In alternating current (AC) measurements, the term immittance denotes the electric -> impedance and/or the electric admittance of any network of passive and active elements such as the resistors, capacitors, inductors, constant phase elements, transistors, etc. In electrochemical impedance spectroscopy, which utilizes equivalent electrical circuits to simulate the frequency dependence of a given elec-trodic process or electrical double-layer charging, the immittance analysis is applied. 

In Section 7.5, we analyze the double layer charge in a solution as a function of the perpendicular distance from the solid surface. No double layer formations are considered in the Maxwell—Wagner theory (Section 3.5.1). However, in wet systems and in particular with a high volume fraction of very small particles, the surface effects from counter-ions and double layers usually dominate. This was shown by Schwan et al. (1962). By dielectric spectroscopy, they determined the dispersion for a suspension of polystyrene particles (Figure 3.10). Classical theories based on polar media and interfacial Maxwell—Wagner theory could not explain such results the measured permittivity decrement was too large. The authors proposed that the results could be explained in terms of surface lateral) admittance. 

Some authors have used the designation modulus spectroscopy to denote small-signal measurement of M vs. v or co. Clearly, one could also define admittance and dielectric permittivity spectroscopy. The latter is just another way of referring to ordinary dielectric constant and loss measurements. Here we shall take the general term impedance spectroscopy to include aU these other very closely related approaches. Thus IS also stands for immittance spectroscopy. The measurement and use of the complex (< ) function is particularly appropriate for dielectric materials, those with very low or vanishing conductivity, but aU four functions are valuable in IS, particularly because of their different dependence on and weighting with frequency. 

A pH sensor, based on a.c. conductivity measurements of a thin polymer film, has been developed. The sensor consists of a planar interdigitated electrode array coated with a polypyrrole multilayer, built-up using the Langmuir-Blodgett technique. Impedance spectroscopy has been used to investigate the complex admittance of the device when exposed to aqueous solutions of different pH. The experimental data have been fitted to the theoretical response of an equivalent electrical network of capacitors and resistors. A response over the pH range 3.5 to 8 has been measured. 

McKubre and Syrett (1983, 1988) were the first to adapt the method of harmonic analysis for the control of the corrosion rate of cathodically polarized systems. They presented a theoretical description of the problem and developed the measuring technique by making measurements over a wide range of frequencies from 1 Hz to 10 kHz. The method applied by them is known in the literature as harmonic impedance spectroscopy (HIS). It is based on the measurement of the zero, first, second, and third harmonics of the current response of an electrode perturbed by a voltage sinusoid signal. The elaborate mathematical treatment of results theoretically gives the possibility of obtaining admittance data independent of the frequency. The numerical solution of a system of three equations with three unknowns allows the determination of required AE, b, and values, and finally the corrosion current. The authors of the HIS method carried out attempts to determine the corrosion rate of copper-nickel alloys, steel, and titanium under cathodic protec-... 

---