STABILITY OF HYDROGENATED AMORPHOUS-SILICON DEPOSITED AT HIGH-TEMPERATURES WITH A REMOTE HYDROGEN PLASMA

It is demonstrated that the stability of hydrogenated amorphous silicon (a-Si:H) is improved by deposition under the combined conditions of high substrate temperature (e.g., T(D) = 400-degrees-C) and high hydrogen dilution, as are readily achieved in a remote hydrogen plasma reactor. In comparison with optimized films from conventional rf glow discharge deposition (e.g., silane, 230-degrees-C, 2 W), undoped high T(D) films possess a lower midgap defect density, the dark dc conductivity in n-type (phosphorus-doped) films displays higher equilibration temperatures and longer relaxation times at a given temperature with an activation energy of 1.0 eV, and undoped high T(D) films have a lower saturated density of light-induced defects. It is proposed that the ability to achieve the improved stability is a consequence of two effects: (1) the use of hydrogen dilution during deposition to maintain the hydrogen concentration in the film near 10 at. % even at 400-degrees-C and (2) the possibility that at high T(D)'s the hydrogen is more stably incorporated in the random network and/or that the density of weak Si-Si bonds is smaller.