The growth of Y2SiO5:Ce thin films with pulsed laser deposition

Abstract

Y2SiO5:Ce phosphor thin films were grown onto Si(100) substrates with pulsed laser deposition (PLD) using a 248-nm KrF excimer laser. Process parameters were varied during the growth process and the effect on the surface morphology and cathodoluminescence (CL) was analysed. The process parameters that were changed included the following: gas pressure (vacuum (5×10−6 Torr), 1×1−2 Torr and 1 Torr O2), different gas species (O2, Ar and N2 at a pressure of 455 mTorr), laser fluence (1.6±0.1 J cm−2 and 3.0±0.3 J cm−2) and substrate temperature (400 and 600°C). The surface morphology was investigated with atomic force microscopy (AFM). The morphology of the thin films ablated in vacuum and 10 mTorr ambient O2 showed more or less the same trend. An increase in the pressure to 1 Torr O2, however, showed a definite increase in deposited particle sizes. Ablation in N2 gas resulted in small particles of 20 nm in diameter and ablation in O2 gas produced bigger particles of 20, 30 and 40 nm as well as an agglomeration of these particles into bigger size clusters of 80 to 100 nm. Ablation in Ar gas led to particle sizes of 30 nm and the particles were much more spherically defined and evenly distributed on the surface. The higher fluence deposition led to bigger particle and grain sizes as well as thicker layers with respect to the lower fluence. The particle sizes of the higher fluence vary mainly between 130 and 140 nm and the lower fluence sizes vary between 50 and 60 nm. The higher fluence particles consist of smaller particles ranging from 5 to 30 nm as measured with AFM. The surface structure of the thin film ablated at 400°C substrate temperature is less compact (lesser agglomeration of particles than at 600°C). The increase in substrate temperature definitely resulted in a rougher surface layer. CL was measured to investigate the effect of the surface morphology on the luminescent intensities. The increased O2 ambient (1 Torr) resulted in a higher CL intensity compared to the thin films ablated in vacuum. The thin film ablated in Ar gas showed a much higher CL intensity than the other thin films. Ablation at a high fluence resulted in a higher CL intensity. The higher substrate temperature resulted in better CL intensities. The more spherically shaped particles and rougher surface led to increase CL intensities.