a-SiC:H Doped with Reactive Gases and with Ion Implantation
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a-SiC:H DOPED WITH REACTIVE GASES AND WITH ION IMPLANTATION
F.DEMICHELIS, C.F.PIRRI and E.TRESSO Dip. Fisica Politecnico - C.so Duca degli Abruzzi 24, 10129 Torino (Italy) G.DELLA MEA and V.RIGATO Laboratori INFN - Via Romea 4, Legnaro e Unita' INFM Padova (Italy) P.RAVA Elettrorava - Via Don Sapino 120, Savonera Torino (Italy) G.AMATO I.E.N. G.Ferraris - Str. delle Cacce 35, Torino (Italy)
ABSTRACT Boron doped a-SiC:H samples have been obtained both by gas phase doping during film growth and by using ion implantation. All the implanted samples were annealed under vacuum to remove the damage introduced by ion implantation and to produce a dopant diffusion. Physical properties deduced by optical, electrical and structural characterization of the two sets of samples have been compared. Ion implantation technique allows a better control of the dopant dose but increases the compositional disorder and the obtained conductivity values are one order of magnitude lower than those of gas doped samples.
INTRODUCTION Doped amorphous silicon carbide has been a matter of considerable interest over the past years motivated by photovoltaic and opto-electronic applications. The incorporation of thin boron doped films of a-SiC:H into a-Si:H solar cells as a semiconducting window has been one of the major advances in solar technology [1,2]. Usually the p-doped alloys are achieved by directly introducing dopants during the deposition through B2H6 gas diluted in H2. An alternative method is the boron ion implantation after a-SiC:H deposition. The advantages of this last doping system are a better control of dopant doses through ion fluences and the control in dopant profiles through ion energies. However the effects of bombardment damage introduced by the implantation process influence the structure of the films. In this paper we discuss our study on boron doped a-SiC:H samples obtained both by gas phase doping during film growth and by using ion implantation. All the implanted samples were annealed under vacuum to remove the damage introduced by implantation and to produce a dopant diffusion.
Mat. Res. Soc. Symp. Proc. Vol. 219. @1991 Materials Research Society
794
Physical properties deduced by means of optical, electrical and structural characterization of the implanted samples and those prepared by conventional PECVD method are compared.
EXPERIMENTAL
Samples were deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD) in a SiH4 , CH 4, H2 mixture both pure or with addition of varying amount of dopant gas B2H6 , diluted at 1% in H2. Typical discharge conditions include: power density 0.062 WCcm 2 , pressure 40 Pa, substrate temperature 200 °C, SiH 4 flow 70 sccm, CH4 flow 100 sccm, volume part per million (VPPM) of dopant gas varying from 1 103 to 1 104. The choice of the energies for ion implantation of boron in the deposited film, depended on both film's thicknesses and compositions which were determined by means of Rutherford Backscattering Spectrometry and Elastic Recoil Detection Analysis. TRIM [3] calculation
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