Dunkelleitfähigkeit

Dunkelleitfähigkeit refers to the electrical conductivity of a material or device when it is in the dark, meaning in the absence of incident light. This property is particularly relevant for semiconductor devices that are sensitive to light, such as photodiodes, solar cells, and phototransistors. Even in the absence of light, a small amount of current can still flow through these devices. This is known as dark current.

The Dunkelleitfähigkeit is primarily determined by the intrinsic properties of the semiconductor material and the presence of impurities or defects within its structure. In an intrinsic semiconductor, at absolute zero temperature, there are no free charge carriers, and thus no conductivity. However, at room temperature, thermal energy can excite a small number of electrons from the valence band to the conduction band, creating electron-hole pairs. These charge carriers contribute to the dark current.

In extrinsic semiconductors, intentionally added impurities (dopants) create a larger concentration of majority charge carriers (either electrons or holes). While these dopants primarily enhance conductivity under illumination, they also contribute to the Dunkelleitfähigkeit by providing a baseline level of charge carriers even in the dark. Defects in the crystal lattice, such as vacancies or dislocations, can also act as generation-recombination centers, influencing the number of free charge carriers and thus the Dunkelleitfähigkeit.

A low Dunkelleitfähigkeit is generally desirable for many optoelectronic devices. For instance, in a photodiode, a low dark current ensures that the signal generated by light is significantly larger than the background current, leading to a higher signal-to-noise ratio and improved sensitivity. Conversely, a high Dunkelleitfähigkeit can reduce the effectiveness of light detection. Understanding and minimizing Dunkelleitfähigkeit is therefore a crucial aspect of device design and fabrication in optoelectronics.