Formation feature of organic polyelectrolyte layer on illuminated semiconductor substrate

Introduction: The results of studying the formation processes of the Si/SiO$_2$/polyethyleneimine hybrid structure at semiconductor substrate photostimulation during the polyethyleneimine adsorption are presented. The aim of the work was to determine the formation relationships of an organic polyelectrolyte layer onto illuminated semiconductor substrate as well as to describe the electronic processes in a hybrid structure responsible for organic layer parameters. A specific feature of the used approach was taking into account changes in the charge state of Si/SiO$_2$/polyethyleneimine structure interfaces due to illumination as well as taking into account the influence of immobilized polyelectrolyte molecules charge. Thus, the developed model of polyelectrolytes photostimulated adsorption on a semiconductor takes into account the interinfluence of the substrate and the adsorbed layer, which reflects in the calculation of polyethyleneimine adsorption kinetics on the Si/SiO$_2$ semiconductor substrate. Methods and Approaches: To verify the model, we used in calculations experimentally obtained values of the surface potential at each stage of the hybrid structure fabrication. Results and Discussions: The dependence of the thickness change of a polyelectrolyte molecules coating deposited on the surface both of p-Si and n-Si substrates on the time of photostimulated deposition has been obtained. It has been shown that with an increase in the illumination time during adsorption, a decrease in the thickness of the polyethyleneimine layer occurs according to an exponential law. The result is explained by the simultaneous occurrence of photogeneration of charge carriers, their drift into the SiO$_2$ layer under the influence of cationic molecules electric field as well as by the characteristic times of these processes. The experimentally observed smoothing of the polyethyleneimine layer relief and a decrease in its effective thickness during photostimulated adsorption onto a photosensitive semiconductor substrate correspond to model concepts on the dependence of polyelectrolyte coating thickness on the effective charge of substrate surface. Conclusion: The results of the study are useful for understanding the mechanisms and regularities of the organic polyelectrolyte layer formation on an illuminated semiconductor substrate and contribute to the improvement of technologies for fabricating functional layers of hybrid structures “semiconductor-organic coating”.