Coulomb interaction geminate recombination

The course of the recombination processes in a particular system depends on several factors. One of the most important ones is the polarity of the system. Both geminate and bulk recombination processes are strongly influenced by the Coulomb attraction between electrons and cations, and the range of this interaction in condensed matter is determined by the dielectric constant e. The range of the Coulomb interaction in a particular system is usually represented by the Onsager radius, r, which is defined as the distance at which the electrostatic energy of a pair of elementary charges falls down to the thermal level kj,T. 

A long time ago, Hong, Noolandi, and Street [16] investigated geminate electron-hole recombination in amorphous semiconductors. In their model they included the effects of tunneling, Coulomb interaction, and diffusion. Combination of tunneling and diffusion leads to an S(t) oc t 1/2 behavior. However, when the Coulomb interactions are included in the theory, deviations from the universal t /2 law are observed—for example, in the analysis of photoluminescence decay in amorphous Si H, as a function of temperature. 

Due to their close proximity, the electron-hole pair is bound by their mutual Coulomb interaction as shown in Fig. 8.7. When the potential is strong enough, the particles diffuse together, giving geminate recombination. Otherwise the electron and hole diffuse apart and any subsequent recombination is non-geminate. The Onsager (1938) model... 

Fig. 8.7. Onsager model of geminate recombination showing the Coulomb interaction of the photoexcited electron and hole.

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