Reverse Biased P-N Junction
When positive terminal of a voltage source is connected to the n-type region and the negative terminal of the source is connected to the p-type region then the p n junction is said to be in reverse biased condition. When there is no voltage applied across the p n junction, the potential developed across the junction is 0.3 volts at 25°C for germanium p n junction and 0.7 volts at 25°C for silicon p n junction. The polarity of this potential barrier is same as the polarity of voltage source applied during reverse biased condition. Now if reverse biased voltage across the p n junction is increased the barrier potential developed across the p n junction is also increased. Hence, the p n junction is widened. When positive terminal of the source is connected to the n-type region, the free electrons of that region are attracted towards positive terminal of the source because of that more positive impurity ions are created in the depletion layer which makes the layer of positive impurity ions thicker.
At the same time since negative terminal of the source is connected to the p-type region of the junction, electrons are injected in this region. Due to the positive potential of the n-type region the electrons are drifted towards the junction and combine with holes adjacent to the layer of positive impurity ions and create more positive impurity ions in the layer. Hence, the thickness of the layer increases.