Boron doping of amorphous hydrogenated silicon films prepared by r.f. sputtering

• Published in: Thin solid films Vol. 124; no. 1; pp. 49 - 53
• Main Authors: Jousse, D., Saïd, J., Bruyère, J.C.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.02.1985
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/0040-6090(85)90027-6

Amorphous hydrogenated silicon (a-Si:H) films 1 μm thick were prepared at 190 and 250 °C by r.f. sputtering in an Ar-H 2-B 2H 6 gas mixture whose composition Y g = [B 2H 6]/([Ar] + [H 2]) was varied between zero and 10 -2. Measurements of the optical gap E 0 and the dark conductivity σ d give evidence for the existence of three regions as a function of Y g. Up to Y g = 10 -6, the conductivity activation energy E a increases towards the intrinsic value E 0/2. For Y g between 10 -6 and 10 -3, E 0 and E a decrease to 1.5 eV and 0.4 eV respectively, indicating that efficient p-type doping is achieved. At higher diborane concentrations a boron-rich a-Si:B:H compound is formed which is not conductive. The photoconductivity ratio σ ph/σ d reaches its maximum value (of 10 3) at Y g ≈ 10 -6 and drops to unity for Y g ⩾ 10 -4. The loss in σ ph is related to an increase in the density of states near the Fermi level as revealed by the onset of an important hopping conductivity on the σ d curves.