The doping of a-Si:H with liquid boron and phosphorus sources

ABSTRACTThe conductivity control of amorphous hydrogenated silicon (a-Si:H) by incorporation of electron donors or acceptors is prerequisite for the application of these layers in devices. The doping sources B2H6 and PH3 which are usually highly toxic are substituted by not dangerous boron and phosphorus liquid sources based on hydro-carbons. The avoidance of gas cylinders and expensive safety measure techniques is another advantage of these liquids.In this paper we have studied the influence of boron, phosphorus and carbon on the electrical, photoelectrical and optical properties. The layers were produced in a capacitively coupled reactor in a silan-doping gas mixture. The maximum of the dark conductivities (300K) of the p- and n-type a-SiC.,:H layers was 10-5 and 103 (Ωcm)-1, respectively, the activation energys decreases to 0.4 and 0.2 eV respectively. With a high quantity within the range of doping gas in the mixture, the carbon determines the layer properties. At a gas mixture ratio of 1:1 ( silan: doping gas) the optical gap expands to 2.7 eV and the dark conductivity decreases below 10∼13 (Ωcm)-1.