Normal and Anomalous Dember Effect

Using Gärtner's equations, effect of sample thickness on the Cember potential (VD) for strong and weak absorption is discussed. It has been found that for strong absorption, as the thickness of the sample increases, VD tends to a saturation value which decreases as the front-surface recombination velocity increases. For weak absorption, initially the behavior of VD depends upon front and back surface recombination velocities, but for large thickness it becomes independent of them and increases linearly with thickness. When front-surface recombination velocity is large as compared to back surface recombination velocity, a sign reversal can take place. Expressions are obtained for VD(i) when surface recombination is dominant, or (ii) when bulk recombination is dominant, for weak and strong absorption in the case of thin and thick specimens. A physical explanation of anomalous Dember effect is given by considering the contribution of the concentration gradients set up by front, back, and bulk recombinations. It appears that simultaneous measurements of Hall angle and ratio of PME and Dember potential can be helpful in measuring electron-hole mobility ratio.