Surface photovoltage method

The light-induced creation of recombination centers causes the diffusion length to decrease with exposure time as shown in Fig. 3 (Carlson et al., 1984b). The diffusion length was measured by the surface photovoltage method (Dresner et al., 1980), and similar results were obtained from an analysis of device characteristics (Faughnan et al., 1983). 

The diffusion length as a measure of fir in undoped a-Si H is a useful parameter to predict the performance of materials made by different methods. The surface photovoltage method has proven to be a rapid and reliable method of determining the diffusion length, provided provision is made to apply bias light to the sample to the level of one sun. This collapses... 

There are numerous techniques to measure the recombination lifetime. Some of the better known are photoconductive decay (13). diode reverse recovery (14). diode open circuit voltage decay (15). surface photovoltage (JL ) and forward-biased pn junction I-V characteristic (17. I will describe one particular photoconductive decay method, because it is a relatively new, non-contact method that requires no junctions. This makes it very suitable for a large number of measurements as for a process sequence characterization tool. 

For calculating the space-charge conductance (j(F,) we need to know the density of states g E) and the surface potential F,. Under favorable conditions, F, of a free surface can be obtained by the Kelvin probe method or from the saturation value of the surface photovoltage. These methods will be illustrated with some preliminary results obtained on a-Si H. We then shall discuss metastable light-induced changes of the surface potential and conductance. 

If strong illumination produces flat bands at the surface without changing X, that is, without aflfecting the surface dipole layer, then the saturation value of the surface photovoltage measured by the Kelvin method A should be... 

A number of characterization methods for wafers are used today. One group of experiments aims at the purely electronic parameters like DLTS and Photoluminiscence. While DLTS and related measurements give information on the trap energies, methods like surface photovoltage (SPV) or open circuit voltage decay (OCVD) give information on effective diffusion length. 

The surface photovoltage lifetime method (SPV) is a steady-state technique in which optical excitation is used to determine the minority carrier diffusion length. The lifetime must be calculated from the diffusion length through the relation Ln nV attractive technique because it is non-desuuctive. 

Surface photovoltage (SPV) measurements have been used to investigate electronic structures at the semiconductor surfaces for semiconductor-vacuum and semiconductor-gas interfaces. This method is applied to semiconductor-liquid interfaces in case of insulating liquids [39]. 

Table 5-41. Other spectroscopic methods Multiwavelength analysis, NMR, raman spectroscopy, and surface photovoltage spectroscopy. ...

Coating the surface of silicon electrodes with a polymer coating can also be an effective method of stabilizing the electrodes and improving the photovoltage and kinetics of electrode reactions " The polymer film effectively insulates the semiconductor from the superoxide ion and prevents chemical reaction and deterioration. At the same time, the polymer behaves like a surface-bond redox couple to mediate the charge transfer between the semiconductor and the redox species in the solution. Various types of polymers can be used to coat silicon electrodes as shown in Table 6.6. 

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