Improvement of the material properties by employing external rf substrate bias during a-Si:H deposition by a remote expanding thermal plasma

An external rf substrate bias (ERFSB) has been employed during high rate deposition of hydrogenated amorphous silicon (a-Si:H) by means of the expanding thermal plasma (ETP) deposition technique. The effect of the additional generated ion bombardment on the material properties under these high deposition rate conditions has been studied. Employing a moderate ERFSB results in a significant reduction of the incorporation of nanosized voids and opto-electronic active defects. We argue that under these specific deposition conditions an ion induced surface modification mechanism, i.e. the ion-induced displacement of surface atoms, is the mechanism responsible for the observed improvements in the material properties.