The effect of electronic correlations on double photoionization spectra of two-electron impurity centers in multi-well quantum structures

Abstract

Background. Impurities of various chemical elements inevitably arise in the process of manufacturing semiconductor nanostructures, or are introduced purposefully to change their transport and optical properties. Moreover, most of impurities can have not one, but two or more electrons in a bound state. In this case, electronic correlations begin to play an important role, due to which one of the fundamental reactions is possible - the process of double photoionization of an impurity atom. The purpose of this research is to calculate the first ionization potential of a two-electron impurity center in a semiconductor quantum well using the variational method, as well as a theoretical study of the effect of electronic correlations on double photoionization spectra of two-electron impurity centers in multi-well quantum structures. Materials and methods. The binding energy and the first ionization potential of a two-electron atom were calculated by the variational method, where the second ionization potential was taken as an empirical parameter. The expression for the coefficient of impurity absorption of light was obtained in the dipole approximation taking into account the dispersion of the width of the quantum wells. Results. The method of the zero-radius potential is generalized to the case of two-electron impurities with an effective nuclear charge equal to zero in semiconductor quantum wells. Within the framework of a semiempirical model, an analytical expression for the first ionization potential of a two-electron impurity center is obtained by the variational method. In the dipole approximation, the coefficient of impurity absorption of light is calculated for the photoionization of a two-electron impurity in a multi-well quantum structure with one photon. Conclusions. It is shown that, due to spatial confinement in a quantum well in one direction, there is an increase in electron correlations, which leads to higher threshold values of the second ionization potential than in quantum dots and, as a consequence, to more stringent conditions for the existence of two-electron impurity states. It was also shown that a decrease in the influence of the quantum size effect and an increase in the electron correlation in multi-well quantum structures as compared to quasi-zero-dimensional structures lead to a transformation of the absorption curve, which is expressed in an increase in the gap between the peaks of the two-humped profile of the spectral curve.

Keywords

• quantum well
• two-electron impurity centers
• electron-electron correlation
• ionization potential
• double photoionization
• absorption coefficient