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Electrical characterization of low temperature plasma epitaxial Si grown on highly doped Si substrates
Cyril Léon, Sylvain Le Gall, Marie-Estelle Gueunier-Farret, Jean-Paul Kleider, Pere Roca I Cabarrocas
To cite this version:
Cyril Léon, Sylvain Le Gall, Marie-Estelle Gueunier-Farret, Jean-Paul Kleider, Pere Roca I Cabarrocas. Electrical characterization of low temperature plasma epitaxial Si grown on highly doped Si substrates. EPJ Photovoltaics, EDP sciences, 2020, EPJ Photovoltaics, 11, pp.4.
�10.1051/epjpv/2020002�. �hal-02472834�
R
EGULARA
RTICLEElectrical characterization of low temperature plasma epitaxial Si grown on highly doped Si substrates
Cyril Leon
1,2,3,*, Sylvain Le Gall
1,2,3, Marie-Estelle Gueunier-Farret
1,2,3, Jean-Paul Kleider
1,2,3, and Pere Roca i Cabarrocas
3,41
Université Paris-Saclay, CentraleSupélec, CNRS, Laboratoire de Génie Electrique et Electronique de Paris, 91192 Gif-sur-Yvette, France
2
Sorbonne Université, CNRS, Laboratoire de Génie Electrique et Electronique de Paris, 75252 Paris, France
3
Institut Photovoltaïque d’Ile-de-France (IPVF), 30 Route départementale 128, 91120 Palaiseau, France
4
LPICM, CNRS, Ecole polytechnique, IP Paris, 91128 Palaiseau, France
Received: 8 October 2019 / Received in fi nal form: 19 December 2019 / Accepted: 7 January 2020
Abstract. Epitaxial silicon layers were grown on highly doped c-Si substrates using the plasma-enhanced chemical vapour deposition process (PECVD) at low temperature (175 °C). The transport and defect-related properties of these epi-Si layers were characterized by current density-voltage ( J–V ) and capacitance–voltage ( C–V ) techniques. The results show that the epi-Si layers exhibit a non-intentional n-type doping with a low apparent doping density of about 2 10
15cm
3. The admittance spectroscopy technique is used to investigate the presence of deep-level defects in the structure. An energy level at 0.2 eV below the conduction band has been found with a density in the range of 10
15cm
3which may explain the observed apparent doping profile.
Keywords: Capacitance – voltage / current – voltage / impurity pro fi le / epitaxial Si
1 Introduction
Low temperature plasma epitaxy has been developed over the past years. The process, based on the interaction of positively charged clusters with the fi lm surface has been studied experimentally [1,2] and modeled using ab initio simulations [3]. Moreover, thin epitaxial layers have been successfully integrated into heterojunction type solar cells on cristalline silicon (c-Si) wafers [4,5] and successfully transferred to glass substrates [6,7] resulting in devices with energy conversion ef fi ciencies in the range of 6 – 8%.
Modeling the J–V characteristics and external quantum ef fi ciency of such devices has revealed that the defect density in these epitaxial layers should be around 1 10
15cm
3and that ef fi ciencies up to 13% are within reach [8]. In this paper we use current density-voltage ( J–V ) and capacitance – voltage ( C–V ) measurements to study the electrical proper- ties (transport and defect states) of Schottky diodes made with a thin crystalline silicon fi lm grown using epitaxy at 175 ° C on a highly doped c-Si substrate.
2 Fabrication process
Undoped (non-intentionally doped) hydrogenated crystalline silicon layers (epi-Si) were deposited by plasma-enhanced
chemical vapour deposition (PECVD) at 175 ° C from the dissociation of silane-hydrogen mixtures in a hot-wall multi- plasma monochamber reactor [9]. The fi lms were co-deposited on highly doped p
++and n
++(100) oriented crystalline silicon substrates with resistivity values below 0.005 ohm.cm and cleaned either using a standard dip in a 5% HF solution for 30 s or in-situ in the plasma reactor using an SiF
4plasma [10]. In the following, the structures will be denoted “ (epi/p
++)
i” and
“ (epi/n
++)
i” for the epi-Si deposited on p
++and n
++c-Si substrates, respectively (with i the sample number). After deposition the fi lms were characterized by spectroscopic ellipsometry measurements from which their crystallinity and their thickness were determined. Au contacts were thermally evaporated through a shadow mask to de fi ne the area of the devices (1 mm and 2 mm diameter dots). Al contact was deposited on the rear side of the structure. Measurements were performed between the Au and the Al contacts. Table 1 summarizes the growth conditions for the samples presented in this study.
3 Current–voltage measurements
The dark J–V characteristics are shown in Figure 2 for both (epi/p
++)
i(Fig. 2a) and (epi/n
++)
i(Fig. 2b). It can be observed that the (epi/n
++)
iexhibit a single junction behavior with one barrier at one electrode and no barrier at the other one, while the linear current for both polarities in
* e-mail: cyril.leon@geeps.centralesupelec.fr
© C. Leon et al., published by EDP Sciences, 2020
https://doi.org/10.1051/epjpv/2020002 EPJ EPJ Photovoltaics Photovoltaics
Available online at:
www.epj-pv.org