Part 2 : Nanostuctures Module 4 : Transport
Lecture 2 : Direct Recombination
 
Direct Recombination
In a direct band gap semiconductor, the thermal agitation breaks the bonds between neighboring atoms creating electron-hole (e-h) pairs. This thermally generated process of creating carriers is represented by the rate $ G_{th}$ (usually expressed as the number of e-h pairs generated per cm3 per sec).
Fig 4.3 : Direct recombination in direct gap semiconductor.
When an electron makes transition downward from the conduction band to the valence band, an e-h pair gets annihilated and this reverse process is called recombination, represented by the recombination rate $ R_{th}$. In thermal equilibrium, $ R_{th}=G_{th}$, and the condition $ pn=n_i^2$ remains valid.