CHARACTERIZATION OF GRAIN BOUNDARIES IN SILICON SOLAR CELLS. PART 2: EVALUATION OF THE DENSITY OF GRAIN BOUNDARY STATES.

Proceeding from the results for the barrier height of a grain boundary in solar cell material evaluated from the measurement of the zero bias conductance at a bicrystal test structure, the density of grain boundary states and their distribution in energy have been determined. The method is a spectroscopic one and yields a steplike energy distribution. In accordance with theoretical calculations simulating typical energy distributions of the states, we find that the density of states in the middle of the gap is negligible and increases towards the conduction band edge to values of about 10**1**2cm** minus **2 V** minus **1. The capture cross section ratio is found to range from 1 less than equivalent to C//p/C//n less than equivalent to 10. The method is proved to yield definite and unambiguous results by means of additional model calculations.