After a short time, an equilibrium is reached between the diffusion currents (also called recombination currents) and a second, opposing type of current. what causes these secondary currents?

what causes these secondary current is that, the diffusion currents cause buildup of positive charge in the n-type material and negative charge in the p-type material. This makes an electric field.

Explanation:

Solution:

The secondary currents are called drifts currents or generation currents. the charge that moves in the generation currents are called electrons and holes simultaneously generated in the junction zone by thermal excitation.

In context, the temperature measures average kinetic energy. even at room temperature, it is possible for an electron to gain enough energy to cross the band gap of the semiconductor.

When this phenomenon happens, a condition electron abruptly becomes available as does a hole. the electric set up by the diffusion currents then charge the electron and hole out of the junction zone to then n-side and p-side respectively.

The diffusion current cause build up of positive charge in the n-type material and negative charge in the p-type material. this makes an electric field.