Effect of temperature on semiconductor

Effect of temperature on Semiconductor

The electrical conductivity of a semiconductor change appreciably with temperature variations. when the temperature is raised some of the covalent bond in the semiconductor break due to the thermal energy supplied. The breaking of bonds sets those electron free which are engaged in the formation of these bond. The results is that a few free electrons exist in the semiconductor. These free electrons can provide a tiny electric current if potential difference is applied across the semiconductor. This show that the resistance of a semiconductor decrease with the increase in temperature example it has negative temperature coefficient of resistance it may be noted that at room temperature, the current through a semiconductor is too small to be of any practical value.

‌It is important to note that each time a valence electron enter into the conduction band, a hole is created in the valence band. A hole represent missing electron in the covalent bond the holes covalent bond . The holes also contribute to current in a semiconductor.

Hole current
At room temperature some of the covalent bonds in the pure semiconductor break, setting up free electrons. Under the influence of electric field, these free electron contribute electric current. At the same time another current -the whole current- also flow in the semiconductor. When a covalent bond is break due to thermal energy, the removal of one electron leaves a vacancy.

Example:-A missing electron in the covalent bond. This missing electron is called hole which act as a positive charge. For make one electron set free, one hole is created. Therefore, thermal energy creates whole electron pairs ; there being as many holes as the free electrons.

When potential difference is applied across the semiconductor, the free electrons moves towards the positive terminal while the holes drift towards the negative terminal of the supply. Therefore current in a semiconductor is due to the free electrons and holes. it may be noted that current in the external wire is fully electronic i.e. by free electrons.

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