THIN-FILM CDS-CU2S HETEROJUNCTIONS - DARK IV CHARACTERISTICS AND HEAT-TREATMENT

The temperature dependence of I-V curves of thin-film polycrystalline CdS/Cu2S heterojunctions was investigated as a function of heat treatment applied to them. Prior to any heat treatment, the space charge in the CdS is narrow enough so that electrons can tunnel from the bottom of its conduction band and the tunneling current is temperature independent. Considerable Ohmic shunting is caused by thin layers of Cu2S which had formed along the grain boundaries. After heat treatment, the space charge in the CdS widened due to diffusion of Cu from the Cu2S, so that electrons in CdS now require an activation energy to tunnel, and this results in a temperature-dependent tunneling current. Furthermore, the thin layers of Cu2S disappeared from the grain boundaries, thus eliminating the shunting paths which had existed prior to the heat treatment.