Improvement of thin film semiconductor conductivities using a transverse current during deposition

Abstract

The effect of electrical current flow parallel to the surface of a growing semiconductor thin film on the electrical conductivity and microstructure of the deposition was investigated. The depositions were produced by filtered vacuum arc deposition. Conducting Sn-O coatings were produced using a 160 A arc on the Sn cathode, with a background O 2 pressure of 0.8 Pa, while B-doped amorphous Si depositions were produced with 20 A arcs on a B-doped Si cathode. The Sn or Si plasma was extracted through a 122 mm inner diameter annular anode and passed through a 160 mm minor diameter, 600 mm major diameter, quarter-torus magnetic filter with a 14 mT magnetic field in order to remove macroparticles. The thin films were deposited on glass microscope slide substrates held at room temperature. Prior to deposition, silver paint electrodes were applied to the substrate in the form of two parallel bands, separated by 20 mm. A potential difference of 0–36 V was applied between the electrodes during the deposition process, and the current flowing along the deposition could be monitored via a shunt resistor. Transparent Sn-O conductivity increased as a function of the applied voltage, reaching an improvement factor of 9 in comparison with films deposited without an imposed transverse current. Scanning electron microscopy examination of the coating surface revealed the presence of numerous round structures. When no current was rejected during film growth, these structures were arranged randomly on the surface, whereas the structures tended to be aligned in long strings parallel to the current field lines when a current was injected during deposition. X-ray diffraction patterns obtained with the sample aligned with the current injection direction parallel and perpedicular to the X-ray beam reveal distinct differences indicating an anisotropy in the microstructure. Preliminary experiments on B-doped Si films similarly showed an improvement by a factor of 2 in the conductivity with the imposition of a transverse potential difference of 36 V.