Ge quantum dot lattices in alumina prepared by nitrogen assisted deposition: Structure and photoelectric conversion efficiency

Abstract

Thin films comprising three dimensional germanium (Ge) quantum dot lattices formed by nitrogen (N) assisted magnetron sputtering deposition in alumina (Al2O3) matrix have been studied for light harvesting purposes. In order to expand the application of this material it is necessary to reduce germanium oxidation and to achieve stabilization of the germanium/alumina interface. Effects of tuning the N concentration, substrate temperature and Ge sputtering power during the films preparation are monitored. It is shown that the N presence not only reduces Ge oxidation during annealing but also affects the internal structure, size and arrangement of Ge quantum dots. Additionally, the deposition temperature and Ge sputtering power are used to tune the Ge quantum dot size, separation and the regularity of their positions. It is shown that the optical and electrical properties of the films, especially their photo-induced current, and quantum efficiency are strongly tunable by the deposition conditions. Moreover, a significant photo-response and effect of multiple exciton generation effect is observed. The materials presented could be used as a sensitive layer for photodetectors or photovoltaic light harvesting devices. The presented tools can be used for future fine tuning of the material to achieve the optimal quantum efficiency.