CHARACTERIZATION OF ELECTRON TRAPS IN CU2S-CDS POLYCRYSTALLINE CELLS BY CAPACITANCE TRANSIENT MEASUREMENTS

A simple method is proposed to determine the activation energies and the capture cross sections of trap levels in junctions. The method can also be used when the electron trap densities are greater than the donor densities as in the space-charge region of Cu2S-CdS heterojunctions. The technique involves measurement of the time constant associated with each trap level, starting from the initial tangent of the junction capacitance transient at different temperatures. In the evaporated CdS layers of the junctions studied, this method was sufficiently accurate to determine the depth and the capture cross sections of the A, C and D electron traps and to confirm that the C level, produced by doubly ionised sulphur vacancies, is the dominant electron trap in the evaporated CdS layers.