The Minority Carrier MIS SB Cell

The so-called min MIS cell has recently established itself as probably the most important type of silicon MIS cell since it has been demonstrated to have a markedly better V-I characteristic and efficiency than cells working on the thermionic emission of Majority carriers already described  

The theory of this cell has been fully described by Green and his CO workers. An outline of the principles involved will now be given. 

The forward bias dark current of a Schottky barrier diode has already been demonstrated to be caused by the thermionic emission of majority carriers from the semiconductor to the metal. It can be represented by the equation 

This value of may be significantly lower than that found from equation 33 for the thermionic emission of electrons. 

If the thickness of the insulator is reduced below about 10 A the concept of a tunnel MIS diode apparently becomes invalid, based at least on experimental evidence, and these thin structures perform as basic Schottky barriers. Above 28-30 A the diodes behave as equilibrium tunnel diodes. From Fig 7a it can be observed that even in the minority carrier regime under forward bias the region over which ideal p-n junction diode behaviour is predicted is insulator thickness dependent. Since in the case of p-n junctions in silicon under normal AMI illumination about 0.5 - 0.7 V is developed across the junction this means that for significant conversion efficiencies in these mi MIS devices insulator thickness should not exceed about 20 A. At greater thickness there will be some suppression of the photo-current due to the shape of the I-V characteristic rather similar to that observed in p-n junction solar cells with large series resistance. 

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