N and p-type doping of PECVD a-SiC:H obtained under “silane starving plasma” condition with and without hydrogen dilution

Abstract

N and p-type doping of highly structural and chemically ordered a-Si 0.5C 0.5:H films are studied. Ion implantation is utilized as doping technique and the films are obtained by rf plasma chemical vapor deposition (PECVD) in the so-called “silane starving plasma” condition, which plays an important role to improve the structural properties of a-SiC:H films. Since hydrogen plasma improves even more the structural properties of the material, the doping efficiency is studied in two types of a-Si 0.5C 0.5:H samples grown with and without hydrogen dilution of the precursor gaseous mixture. For n-type doping, phosphorus was implanted in concentrations varying between 10 18 and 10 21 cm −3, according to previous theoretical simulations. For p-type doping boron and, for the first time in a-SiC:H technology, boron difluoride (BF 2) were implanted, both with a fixed concentration of 10 20 cm −3. The electrical characterization for phosphorus doping shows that the conductivity of the films increases with increasing impurity concentration and, in the best case a room temperature dark conductivity of ∼10 −4 (Ω cm) −1 and an dark conductivity activation energy of 0.1 eV were obtained. For p-type doping the results indicate that BF 2 + is much more efficient than boron, which is related to the production of a shallow doped layer, in accordance to observations in c-Si. In this way a p-type dark conductivity of ∼10 −1 (Ω cm) −1 and energy of 20 meV were obtained.