Modified Triode Plasma Configuration Allowing Precise Control of Ion-Energy for Preparing High Mobility a-Si:H

Abstract

We have previously shown that the carrier drift mobility in amorphous silicon can be enhanced by optimizing the ion-bombardment energy during growth on conducting substrates. However, there exists a lack of reproducibility of samples exhibiting high mobility which we attribute to the rf field induced fluctuation of the plasma potential in a conventional (T_e} ≈ 2eV) silane plasma. Here we introduce an enclosed plasma configuration that allows us to confine the effect of the rf field and therefore obtain a low-electron-temperature (T_e ≈ 0.1 eV) silane plasma as determined from Langmuir probe measurements. The measured ion-energy distributions correlate with those for electrons and the mean ion-energy can be controlled by biasing the substrate which allows us to reproducibly fabricate high drift mobility amorphous silicon.