Synthesis of indium oxi-sulfide films by atomic layer deposition: The essential role of plasma enhancement

Cathy Bugot,Frédérique Donsanti,Nathanaëlle Schneider,Daniel Lincot

doi:10.3762/bjnano.4.85

Abstract

This paper describes the atomic layer deposition of In2(S,O)3 films by using In(acac)3 (acac = acetylacetonate), H2S and either H2O or O2 plasma as oxygen sources. First, the growth of pure In2S3 films was studied in order to better understand the influence of the oxygen pulses. X-Ray diffraction measurements, optical analysis and energy dispersive X-ray spectroscopy were performed to characterize the samples. When H2O was used as the oxygen source, the films have structural and optical properties, and the atomic composition of pure In2S3. No pure In2O3 films could be grown by using H2O or O2 plasma. However, In2(S,O)3 films could be successfully grown by using O2 plasma as oxygen source at a deposition temperature of T = 160 °C, because of an exchange reaction between S and O atoms. By adjusting the number of In2O3 growth cycles in relation to the number of In2S3 growth cycles, the optical band gap of the resulting thin films could be tuned.

Highlights

Chalcopyrite-type thin film solar cells that are based on a Cu(In,Ga)Se2 (CIGS) absorber have reached high efficiencies, up to 20.3% [1] in 2011 and 20.4% [2] on flexible substrates in 2013
Most Cd-free buffer layers are based on zinc and indium-compounds, with current record efficiencies obtained by chemical bath deposition (CBD, 19.7% and 19.1% for Zn(S,O,OH) [4,5], 15.7% for In(S,O,OH) [6]) or atomic layer deposition (ALD, 18.5% for Zn(O,S) [7], 18.1% for (Zn,Mg)O [8], 16.4% for In2S3 [9], and 18.2% for (Zn,Sn)O [10])
In this study we reported the atomic layer deposition of In2(S,O)3 films by using In(acac)3, H2S, and either H2O or O2 plasma as oxygen sources

Summary

Introduction

Chalcopyrite-type thin film solar cells that are based on a Cu(In,Ga)Se2 (CIGS) absorber have reached high efficiencies, up to 20.3% [1] in 2011 and 20.4% [2] on flexible substrates in 2013. ALD is based on sequential self-saturated reactions that allows the conformal and uniform growth of thin films with a high control of their properties [1315]. It is a suitable technique for the deposition of buffer layers. Oxygen-doping of In2S3 films is known to increase their optical band gap value [6,17,18]. By using the spray pyrolysis technique, Maha et al have inserted sulfur atoms in In2O3 thin films and obtained optical band gaps in the range from 3.85 to 3.96 eV [18]. It is widely used to enhance the thin-film deposition of materials such as Al2O3, ZnO, Ta2O5, TiN, TaN and SiNx [19]

Results

Discussion

Conclusion