Brytavskyi I. Influence of inhomogeneous localized charge distribution in nonideal heterojunction CdS-Cu2S on its photovoltaic properties

The thesis is devoted to theoretical generalization, modeling and control of accumulation and re-read signal effect in optical sensors based on nonideal heterostructures. Question concerning minimization of sensor photovoltaic properties time degradation is also discussed. The work is dedicated to the analysis of the characteristics of sensory properties and component composition of micromorphology of thin-film heterojunction CdS-Cu2S In this regard, a complex research aimed at detailing the energy distribution of deep trap centers in the bandgap of CdS, modeling processes in the tunnel barrier layer, determining microstructure characteristics of the samples chemically modified phase composition, degradation study sensory properties and how to minimize it. The paper presents a model that describes the kinetics of concentration of positive charge, accumulated in deep traps after photoexcitation and takes into account both thermal and tunnel holes release mechanisms. Numerical calculations of localized charge distribution changes over time, found out that this distribution in terms of dynamic equilibrium has an exponential character. Close compliance between calculated and experimentally obtained dependences was demonstrated. The mechanisms of signal relaxation, associated with the removal processes of nonequilibrium charge from the space charge region of the image sensor on the basis of non-ideal heterojunction were investigated. The mechanism of the observed two-stage process was determined. Microscopic techniques (AFM, SEM) were used to estimate heterojunction properties (grain size, roughness) and their relations with heterojunction processing parameters. Novel results concerning CdS-Cu2S heterojunction surface morphology and impurities depth distribution were obtained. In particular, the question of observed variation of surface photosensitivity and components interdiffusion on heteroborder was clarified. Also the comparison of samples formed by two different methodics (electrodynamical spraying and vacuum evaporation techniques) was made. X-Ray diffraction (XRD) was performed in order to detect CuxS compounds at CdS-Cu2S heterojunctions.