The Growth of, and the Formation of Grain Boundaries in, Cu2 S  Films Grown on Faceted Single Crystal CdS Substrates

Abstract

It is shown that large angle grain boundaries are formed in the Cu2S film at the intersection of adjacent prismatic normalCdS planes and that small angle grain boundaries are formed at the intersection of adjacent prismatic and non‐prismatic normalCdS planes and at the intersection of a nonprismatic plane with the basal plane. The large angle grains are formed because the orthorhombic Cu2S c‐axis is at most a 2‐fold axis whereas the normalCdS axis is a 6‐fold axis. It is shown that the open‐circuit voltage is reduced in the vicinity of these grain boundaries. The small angle grain boundaries form because the effective c/a axis of Cu2S is different than the c/a axis of normalCdS so that the Cu2S is distorted when it is made to conform with the normalCdS substrate. The open‐circuit voltage in the vicinity of these grain boundaries did not noticeably decrease. It is also shown that the growth rate and morphology of the Cu2S films depend on the orientation and morphology of the normalCdS substrate.