Conductivity measurements steady-state electronic current

The net photocurrent and the quantum yield are a function of a number of competing processes " as shown in Fig. 1.22. For an n-type semiconductor, the externally measurable current i is the difference between the photocurrent and the forward current of electrons. The electron current is decreased to zero under certain anodic bias. While the flux of holes to the surface is exclusively controlled by the solid-state properties, all the other reaction steps depend on the surface properties of the semiconductor. The holes arriving at the surface can either (i) transfer to an electron donor in the solution, (ii) be trapped at the surface states, or (iii) recombine with electrons in the conduction band in the depletion region or at the surface. Process (iii) does not generate current in the external circuit, whereas process (ii) produces only transient current charging up the surface states. Only process (i) produces steady photocurrent. The measured photocurrent /ph can therefore be different from the flux of holes to the surface due to these processes. 

Use of a metal-semiconductor Schottky diode allowed for the measurement of the steady-state current from the continuous flow of ballistic charge carriers generated by the absorption of photons. Schemes of the photovoltaic device are also described in Fig. 10.9a. To generate electric current through the device, these electrons need enough energy to travel over the Schottky barrier and into the Ti02 conduction band. 

The photo-ionic detection consists in the measurement of the conduction modification of a solution, due to an optical resonant interaction of a laser beam with the species of the solution [1, 2], The optical pulse modifies the distribution on the different electronic energy levels, and therefore the steady-state current. 

A method analogous to the H-W method is used to determine the ionie conductivity O . It is based on blocking the electronic current through the MIEC in steady-state conductivity measurements. Such a blocking electrode is a SE backed by a reversible contact. For determining o(Mj ) in a MIEC the cell configuration would be, e.g.,... 

The first effect of the electronic conductivity on emf measurements was demonstrated by Wagner.A short description is given in this section for an oxide SIC. Electrons and oxygen ions are assumed to be the predominant species. Under steady-state conditions, without dc current. Equations (10.15) or (10.16) can then be written... 

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