Effects of Temperature on Conductivity of Semiconductor
The conductivity of a semiconductor is significantly affected by temperature. The relationship between temperature and conductivity in semiconductors can be understood through the following key points:
Increase in Conductivity with Temperature (Intrinsic Semiconductors):
In intrinsic semiconductors (pure semiconductors without intentional doping), as the temperature increases, the electrical conductivity also increases.
This behaviour is primarily due to the increased thermal energy provided to electrons. As the temperature rises, more electrons in the valence band gain enough energy to move to the conduction band, creating additional charge carriers (electron-hole pairs).
The increased number of charge carriers results in a higher electrical conductivity because there are more carriers available for current flow.
Temperature Coefficient of Intrinsic Semiconductors:
The relationship between temperature and conductivity in intrinsic semiconductors can be quantified using the temperature coefficient of intrinsic carriers (α).
The temperature coefficient (α) is positive, indicating that as temperature rises, the intrinsic carrier concentration increases, and thus, the electrical conductivity increases.
Decrease in Conductivity with Temperature (Extrinsic Semiconductors):
In extrinsic semiconductors (doped semiconductors), the behavior depends on the type of impurities and the doping concentration.
In N-type semiconductors (doped with donor impurities), as the temperature increases, the conductivity tends to increase because more thermal energy allows more electrons to participate in conduction.
In P-type semiconductors (doped with acceptor impurities), the conductivity tends to decrease with rising temperature. This is because as the temperature increases, more electrons in the valence band are excited to the conduction band, leaving behind more holes. The increased hole concentration reduces the overall conductivity.
Overall Temperature Dependence:
The temperature dependence of semiconductor conductivity is generally more significant than in conductors, where increased temperature typically leads to increased conductivity.
The behavior of semiconductors at higher temperatures is complex and depends on factors such as bandgap energy, carrier mobility, and doping concentration.
At very high temperatures, intrinsic semiconductors can become intrinsic conductors (similar to metals) as a result of the increased carrier concentration and mobility.
Applications and Considerations:
Understanding the temperature dependence of semiconductor conductivity is crucial for designing and operating electronic devices reliably.
Thermal management is essential in electronic circuits to control temperature-related variations in semiconductor performance.
In some cases, such as thermistors, the temperature dependence of a semiconductor's resistance is deliberately utilized for temperature sensing and control applications.
In summary, the conductivity of semiconductors is influenced by temperature, and the exact effect depends on the type of semiconductor (intrinsic or extrinsic), the doping type and concentration, and the bandgap energy. Intrinsic semiconductors generally exhibit increased conductivity with rising temperature, while extrinsic semiconductors may show varied behavior based on their specific characteristics.