Abstract
The conductivity and Hall effect of micro-crystalline selenium have been measured as a function of iodine content under two different conditions of crystallization, over a range of temperatures The conductivity increases with iodine concentration, a maximum being reached at a concentration of about 0.03 atomic per cent. The Hall effect shows this increase to be due to an increasing mobility, the carrier concentration remaining nearly constant The effect of carrying out the first crystallization of the amorphous Se at 175° c. instead of 110° C is to reduce the conductivity by a factor of ten This is due to reductions in both mobility and current carrier concentration. With increasing temperature the mobility rises and the carrier concentration falls, the product of the two resulting in a rising conductivity with samples crystallized at 175° and a slightly falling conductivity with samples crystallized at 110° C The results are discussed in terms of the grain structure of the material Microscopic examination has shown that the grain size is different for different crystallization temperatures and it is suggested that larger crystals contain a smaller density of acceptor centres. The fall in carrier concentration with increasing temperature is thought to be due to the relief of stress set up due to anisotropic contraction when the material is cooled from the annealing temperature. The low absolute value of the mobility and its rise with temperature are ascribed to intergranular high resistance barriers.
Published Version
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