LIGHT ABSORPTION of SMALL CdS QUANTUM DOTS

Abstract

The aim of article is to analyze the conditions of the interface states arise which caused by the polarization trap, and determine the impact of these conditions on the light absorption. Therefore, it was determined the energy of interface states caused by polarization charges arising on heteroboundaries. For calculations we took into account two models: the transition layer on the interface and his absence. In both cases, we shown that polarization traps exist, which can capture the electrons in the case of the small size of quantum dots. The energy spectrum of surface states was calculated by the Ritz variational method. A comparison of these energy states with energy internal states was made.The internal states are defined accurately using the effective masses approximation and the model of rectangular potential wells and barriers. This made it possible to conclude that for the real quantum dot size, the ground state of an electron is always in the internal states of quantum dot. Excited state is not affected. The dependence of the surface states energy on the quantum dot size was obtained. The corresponding energy of these states increases with decreasing of the quantum dot size. This is due to the polarization dependence of the depth of the trap sizes.We calculated matrix elements of the dipole moment of interlrvel transitions into surface states. The light absorption coefficient caused by the interlrvel transitions was defined as a function of the electromagnetic wave frequency. In the final formula of absorption coefficient, we take into account the quantum dots size distribution. It is shown that absorption bands which corresponds to electron transitions into surface states is much smaller than the absorption bands caused by transitions between inner states.