ELECTROABSORPTION MEASUREMENTS AND BUILT-IN POTENTIALS IN AMORPHOUS-SILICON P-I-N SOLAR-CELLS

We present a technique for using modulated electroabsorption measureme nts to determine the built-in potential in semiconductor heterojunctio n devices. The technique exploits a simple relationship between the se cond-harmonic electroabsorption signal and the capacitance of such dev ices. We apply this technique to hydrogenated amorphous silicon (a-Si: H)-based solar cells incorporating microcrystalline Si p(+) layers. Fo r one set of cells with a conventional plasma-deposited intrinsic (i) layer we obtain a built-in potential of 0.98+/-0.04 V; for cells with an i layer deposited using strong hydrogen dilution we obtain 1.25+/-0 .04 V. We speculate that interface dipoles between the p(+) and i laye rs significantly influence the built-in potential, (C) 1996 American I nstitute of Physics.