HEAT EXCHANGES AND COLUMNAR GROWTH IN ELECTRON-BEAM EVAPORATION OF SILICON FILMS FOR SOLAR CELL APPLICATIONS.

Heat exchanges in electron-beam evaporation of polycrystalline Si films are studied for the first time using an electrical model. The analysis is useful for evaluating the growth kinetics of the film which influence the diameter of the columnar structure. It is shown that Si deposition causes an unsteady thermal state resulting from the radiative interaction of the substrate with the source and adjoining system parts. The calculated values of the heat exchange rates between source, substrate and enclosure, and the temperature gradient along the substrate, are in reasonable agreement with the measured parameters. Columnar films up to 27 mu m in thickness, 6 mu m in column diameter, and with left angle bracket 110 right angle bracket preferred orientation, have been produced by e-beam deposition of Si on Al-coated substrates at temperatures ranging from 400 prime to 600 degree C. SEM micrographs are included showing columnar structure, effects of etching, and previously unreported growth features and the dependence of the column axis on the direction of the vapor stream. The influence of deposition parameters on the column diameter is discussed. The absence of Al near the film surface, as determined by Auger analysis, precludes the possibiliy of liquid-phase crystallization in the present study.