Question

Why does the small current flowing through a reverse. biased diode depend much more strongly on temperature than on the applied (reverse) voltage?

Short answer

The small current through a reverse-biased diode relies more on temperature rather than on the applied reverse voltage because the increase in temperature causes a significant increase in the excitation of charge carriers, thereby increasing the current, while the applied reverse voltage barely affects the current.

Step-by-step solution

Understanding a Reverse-Biased Diode

In electronics, a diode is a device that allows current to flow in one direction but not the other. When the diode is reverse biased, the direction of electric field is in the same direction as the direction of diffusion. This means the current through the diode is very small, mainly due to minor carriers.

Effect of Voltage on Current in a Reverse-Biased Diode

The current flowing through a reverse-biased diode is almost constant irrespective of the applied reverse voltage. This is because the electric field generated by the reverse voltage is unable to overcome the force of the existing electric field to cause any significant movement of charges.

Effect of Temperature on Current in a Reverse-Biased Diode

However, as the temperature increases, the thermal energy provided to the charges results in an increase in current. This is because the increased temperature helps to excite more charge carriers from the valence band to the conduction band in the semiconductor material of the diode, causing an increase in the reverse current.

Conclusion

Therefore, the small current flowing through a reverse-biased diode is more dependent on the temperature than the applied reverse voltage, because the temperature affects the amount of charge carriers that can overcome the force of the electric field, and thus, flow as current.

Key concepts

Temperature Dependence

A reverse-biased diode is highly sensitive to changes in temperature. The small leakage current that flows through such a diode increases significantly with a rise in temperature. This occurs because higher temperatures provide more energy to electrons, allowing more of them to jump from the valence band to the conduction band of the semiconductor material.
As these electrons become mobile, the number of available charge carriers increases, boosting the current.
Contrary to voltage, which maintains a relatively constant current when the diode is reverse-biased, temperature plays a pivotal role in influencing current levels due to its impact on charge carrier activity.

Thermal Energy

Thermal energy is simply the energy that comes from the temperature within a system. In the context of a reverse-biased diode, this energy has pronounced effects on the semiconductor's electrons. When the diode's temperature rises, the thermal energy provided excites more electrons, allowing them to overcome the potential barriers.
The energy transferred to electrons from vibrations in the diode lattice increases, causing more electron-hole pairs to form. As more pairs are generated, the current also rises. This movement due to thermal excitation is a key reason why the current in a reverse-biased diode shows a strong temperature dependency.

Minor Charge Carriers

In a reverse-biased diode, the minimal current flow is largely dictated by minor charge carriers. These carriers include minority electrons in p-type material and minority holes in n-type material. Under reverse bias conditions, majority carriers are repelled, but minority carriers can still cross the junction, facilitating the small but crucial current.
Minor charge carriers are greatly influenced by temperature. As temperature rises, so does the energy available to these carriers due to increased thermal energy.
Consequently, more minor carriers are mobilized, which directly affects the leakage current in the diode.

Semiconductor Material

The semiconductor material used in diodes, like silicon or germanium, has intrinsic properties that determine how it responds to temperature and voltage. It is the arrangement and behavior of electrons within this material that define its function.
At lower temperatures, semiconductors exhibit less movement of charge carriers. However, as temperature increases, more electrons gain sufficient energy to participate in conduction.
The way semiconductor materials react is crucial to understanding why reverse-biased diodes exhibit temperature-dependent behavior. They essentially form the structural basis that allows for the activation of more charge carriers as temperature conditions heighten.