(iii) Bir-Aronov-Pikus mechanism:

The Bir-Aronov-Pikus (BAP) mechanism is a source of spin relaxation of electrons in semiconductors where there is a significant concentration of both electrons and holes (see Figure 8.1). In such a case, an electron will be usually in close proximity to a hole, so that their wavefunctions will overlap. This would cause an exchange interaction between them. If the hole's spin flips, then the exchange interaction will cause the electron's spin to flip as well, leading to spin relaxation.

Figure 8.1: Schematic drawing of BAP mechanism. The exchange interaction between electrons (filled circles) and holes (open circles) causes the electron spins to precess along some effective magnetic field determined by hole spins. In the limit of strong hole spin relaxation, this effective field randomly changes before the full precession is completed, reducing the electron spin relaxation [1].

The expression for spin relaxation rate of electrons due to the BAP mechanism in bulk semiconductors was derived by Pikus et al [2] and the expression is

Where n_f (n_b) is the concentration of free (bound) holes, E is the electron energy in the conduction band, m* is the electron effective mass, and

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