Modified triode plasma configuration allowing precise control of ion-energy for preparing high mobility a-Si:H

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 ≈ 0.1eV) 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.