Capacitance decay after termination of light was measured on AlxGa1−xAs/GaAs heterostructures with p-n junctions. It has been shown that the decay can be well expressed by two curves of stretched exponential forms; exp[−(t/τ)β]. The temperature dependence of the characteristic time τ of each of the two curves was determined in the range from 15 K to 60 K. The dependence follows the theoretical relation for electron capture dominated by tunneling via multiphonon emission. The estimated capture parameters show a strong electron-phonon coupling of two DX centers. Possible relation of these centers to tin is discussed.