Structural dependence of electrical properties of Ge films prepared by RF magnetron sputtering

This paper investigates the electrical properties of non-hydrogenated and hydrogenated germanium thin films deposited on silicon nitride coated glass in order to develop a material for the bottom cells of low cost monolithic tandem solar cells. Films were deposited by RF magnetron sputtering over a series of substrate temperatures up to 500A degrees C. A structure-dependent conduction property of germanium films was found. As the substrate temperature increased from 255 to 400A degrees C, both series of films first showed n-type conductivity with progressively increasing room-temperature dark resistivity that peaks around the type switch. Upon attaining p-type character the resistivity decreased rapidly with further increase in T (s). Accompanying these trends, the film grain orientation evolved from predominantly (220) to (111).