Double photoionization of two-electron impurity centers in quasi-zero-dimensional structures

Background. The interest in impurity atoms, possessing two electrons, is associated with the fact that they appear to be the elementary systems within which double ionization by a single photon is possible. The second electron's detachment from the atom occurs due to the recoil effect after the first electron's departure. The aim of the study is to calculate the first potential of ionization of the two-electron impurity center in a quantum dot using the variation method, and to theoretically research the features of the double photoionization of two-electron impurity centers in a quasi-zero-dimensional structure. Materials and methods. Calculation of the binding energy and the first potential of ionization of a two-electron atom is carried out by the variation method, where the second potential of ionization acted as an empirical parameter. An expression for the coefficient of impurity light absorption was obtained in dipole approximation taking into account quantum dot radius dispersion. Results. The authors generalized the method of zero radius potential for the case of two-electron impurities in quantum dots with nuclear charge equaling to zero. In the framework of a semiempirical model, using the variation method the authors obtained an analytical expression for the first potential of ionization of a two-electron impurity center. In dipole approximation the researchers calculated the coefficient of impurity light absorption during photoionization of a two-electron impurity by a single photon. Conclusions. It is shown that a dimensional constraint in quasi-zero-dimensional structures promotes occurrence of two-electron impurity centers and in case a zero charge of the atomic core. Double photoionization of impurities leads to occurrence on a spectral absorption curve of a typical two-humped profile with the peak disposition significantly depending on the quantum dot's average radius.