SAS Offers for Commercial Sphere
Versatile transient charge processor (VTCP).
It deals with processing transient charges of the system under test equipped with two (three) electrodes in response to excitation pulses superimposed on a quiescent or swept bias. Apart from the sample holder selected, the setup comprises three modules:
- stand-alone charge-to-voltage converter (CVC),
- main application card (MAC),
- subsidiary application card (SAC).
Before passing to details, let us mention that we deal with a versatile facility which integrates several table-top powerful instruments, reducing to a minimum space and costs:
- spectrometer of deep defect levels (charge DLTS - commercially not available),
- feedback charge capacitance- and current-voltage meter (C-V, I-V),
- multimode voltammetric analyser (double-step voltcoulometry, differential pulse voltammetry, steady-state voltammetry, derivative voltammetry).
Dielectric and polarization properties of insulators Knowing precisely the geometry of the capacitor containing either solid or liquid dielectric between its electrodes one can define the time-dependent permittivity as an equivalent (complement) of the frequency domain permittivity determined by ac measurements. From the total amount of the collected charge concentrations of complexes (e. g. dipoles) contributing to dielectric polarization can be obtained.
Spectroscopy of defects in semiconductors
Nowadays there is a huge number of electronic devices which could be explored by the charge DLTS method from the point of view of defects in the band gap of many types of semiconducting materials. The commercially available DLTS spectrometers use exclusively relatively slow capacitance meters as input units. Our CVC input unit is capable of collecting charges down to a few microseconds, a time region not accessible by the capacitance meters. Moreover, the charge DLTS has a complementary spatial detection sensitivity to its capacitance counterpart, a valuable feature if reconstructing spatial density profiles of defects in the vicinity of surfaces (interfaces). Extensive charge DLTS experiments are being conducted on thin films of amorphous undoped (hydrogenated) Si for solar cells, a material known for its complex spatial and energetical distribution of electron traps.
Analytical electrochemistry of solids and liquids
The multimode feature of our setup, if viewed as a voltammetric (polarographic) analyser, makes it suitable for electroanalytical studies of electrically active species (speciation) in waters and drinks even in situations where a supporting electrolyte cannot be added for whatever reasons. In addition, our instrumentation is especially suitable for assessing real concentrations of the species while facing significant deviations of the reaction kinetics from the ideal one.
There is quite a new branch of the voltammetry, known as solid- state voltammetry. It adheres to solids containing high densities of „redox“ centers (centers exhibiting at least two different charge states), responsible for hopping of charge carriers between adjacent sites at relatively low temperatures. As an accompanying attribute, a steady-state voltammetric wave is observed, from which the density of the centres as well as the diffusion coefficient of the hopping charge carriers may be deduced. This phenomenon is well pronounced if a concentration gradient of the centres could initially be induced in an electrochemical way.
The VCTP instrument characterized above is now commercially available with two types of sample holders (cells). For applications labelled A and B, respectively, in the previous paragraph there is a simple evacuated metallic cryostat available, covering the temperature range 80 K – 450 K. As an alternative we are able to supply an electrochemical cell utilizing a carbon fibre microelectrode as the working electrode. A new version of the setup in the form of a condensed single application card is in preparation as a prototype.
We are ready to start both types of experiments on request for either the spectroscopy of defects in insulators and semiconductors, or speciation of metals and acids in waters or drinks. The outcome would be a corresponding protocol, other possible form could be offering the complete VCTP setup to potential customers for buying it.