SEMICONDUCTOR DIODE

SEMICONDUCTOR DIODE

The semiconductor diode is formed by simply bringing an n- type and p- type materials together. At the instant the two materials joined together the electrons and holes in the region of junction will combine resulting in a lack of carriers in the region near the junction.

This region of uncovered positive and negative ions is called the depletion region due to the depletion carriers in this region.

There are three possible type of diode operating conditions. They are:

(a)  No bias

(b)  Forward biasing

(c)  Reverse biasing

NO BIAS

Under no-bias condition, any minority carriers in the n-type material that find themselves within the depletion region will pass directly into the p-type material. The closer the minority carrier is to the junction, the greater the attraction for the layer of negative ions and the less the opposition of positive ions in the depletion region of the n-type material. In the absence of an applied bias voltage, the net flow of charge in any one direction for a semiconductor diode is zero.

REVERSE BIAS

If an external potential V volts applied across the p-n junction such that the positive terminal is connected to the n-type material and negative terminal to the p-type material. The number of uncovered positive ions in the depletion region of the n-type material will increase due to the large number of free electrons drawn to the positive potential of the applied voltage. The net effect is the widening of the depletion region which will establish a great barrier to the majority carriers, effectively reducing the majority carrier flow to zero. However, number of minority carriers entering depletion region will not change, resulting in minority carrier flow. The current that exists under reverse bias conditions is called the reverse saturation current and is represented by Is.

 

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