Room-temperature photoluminescence from Tb3+ ions in SiO2 and a-SiC:H thin films deposited by magnetron co-sputtering

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Abstract

The laser excited photoluminescence (PL) of SiO2 and a-SiC:H thin films doped with Tb deposited by co-sputtering has been studied. In the case of SiO2:Tb the PL is due to 4f–4f transitions of Tb3+ ions starting from the 5D4 level which is resonantly excited by the 488 nm Ar+ laser line. The PL in this case has no temperature quenching from 18 K up to room temperature. The inhomogeneous broadening of the PL bands predominates over the homogeneous one. In the case of a-SiC:H:Tb a broad band covering the whole visible spectrum is observed. It is tentatively assigned to a recombination centre created by the Tb impurity.

Introduction

Rare earth ions in silicon based materials have been the object of much interest recently. This is stimulated by the aim to develop light emitters integrated in the silicon electronics. Er3+ has drawn the most attention because one of its most efficient radiative intra-4f transitions is at 1.5 μm, which is a very important wavelength for telecommunications. Tb3+ is a rare earth ion, which has strong radiative intra-4f transitions in the visible. That is why it is a potential candidate for visible LEDs. H. Amekura et al. [1] have demonstrated visible photoluminescence from thin SiO2 layers implanted with Tb. Magnetron co-sputtering is an alternative method for obtaining rare earth ion containing films which gives a uniform depth distribution of the impurity atom. In this paper, we study the photoluminescence (PL) properties of thin SiO2:Tb and a-SiC:H:Tb films prepared by magnetron sputtering.

Section snippets

Experiment

The thin films of SiO2:Tb were co-sputtered in Ar. The target consisted of a silica (SiO2) plate with a varying number of Tb chips placed on it. For the a-SiC:H:Tb films a complex target of c-Si with graphite and Tb chips placed on it was used. The sputtering was performed in Ar and H2. Crystal silicon substrates were used. The thickness of the films was 1000 nm. The Tb concentration in the films was measured using RBS. Films of SiO2 with Tb concentrations between 0.37 and 13.5 at.% were

SiO2:Tb

A typical room temperature PL spectrum of the SiO2:Tb thin films is shown in Fig. 1. It consists of three characteristic bands which are assigned to the following 4f–4f transitions of the Tb3+ ion, 5D4→7F5 (∼545 nm), 5D4→7F4 (∼590 nm), 5D4→7F3 (∼620 nm). The 488 nm laser line excites resonantly the 5D4 level of the Tb3+ ion and the radiative transitions to the levels lying just above the ground level are observed in this experiment. The first of these transitions is the strongest and it has a

Conclusion

We have demonstrated that thin films of SiO2 and a-SiC:H containing Tb and exhibiting room temperature photoluminescence can be prepared by magnetron co-sputtering. The room temperature visible PL of the SiO2:Tb samples increases up to concentrations of 2.5 at.% Tb and then starts to fall. It shows no temperature quenching from 18 to 300 K. It is due to intra-4f transitions in the Tb3+ ions. It is proposed that the PL in a-SiC:H is connected to a recombination centre introduced by the Tb

Acknowledgements

This study was supported by the Bulgarian National Scientific Fund under Contract X-903.

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