Yasuo Matukura

Anisotropic Stress Effect of Silicon pn Junctions

The effect of large anisotropic stress on shallow silicon pn junctions is investigated. Anisotropic stresses are applied perpendicularly to four types of junction planes, each having an orientation of (100), (110), (211) or (111). The current through the region stressed increases exponentially with the increasing stress, and its dependence on the applied voltage is similar to that of a normal pn junction. Current under the stressed condition is shown empirically as follows: Is=(1-α)I+αAJ0*exp (W/W0)[exp (qV/mkT)-1]. W0 is the characteristic weight, which can be a measure of the sensitivity to the increased current. The characteristic weight is found to be minimum for the (100) pn junction and maximum for the (111). An influence of the spreading resistance on the current through the stressed region has been considered, and possible explanations of the anisotropic stress effect are given.

Some Factors Influencing on the Anisotropic Stress Effect of pn Junctions

The anisotropic stress effect in silicon and germanium pn junctions is studied for various values of factors, such as stress, junction depth from the surface, resistivity and dislocation density of bulk semiconductor, and temperature. On the basis of the empirical formula for this effect, the most important parameters, W0 and J0*, are obtained from the dependence on the above mentioned factors. W0 increases linearly with the increase of junction depth and slightly with the increase of resistivity, while it does not depend on the dislocation density. On the other hand, J0* does not depend on the junction depth, but it increases a little with decreasing impurity concentration and dislocation density. The contribution of stress to the effect changes stepwise during successive increase of the stress. The results are discussed in connection with the strain created of the stress. The results are discussed in connection with the strain created by stress and the recombination current due to the strain, but at the present stage it is difficult to explain the temperature dependence of the anisotropic stress effect.