Cathodoluminescence Study of Gadolinium-Doped Yttrium Oxide Thin Films Deposited By Radio-Frequency Magnetron Sputtering

Abstract A multi-layer gadolinium-doped yttrium oxide thin film was deposited in a combinatorial fashion on a Si (001) substrate using radio-frequency magnetron sputtering. Alternating layers of Y 2 O 3 and Gd were deposited for a total of 9 layers. The film was homogenized in composition by an 850 o C 12 hour thermal treatment producing a range of composition from Y 1.96 Gd 0.04 O 3 -Y 1.54 Gd 0.46 O 3 in a single film. Ultraviolet emission with a peak wavelength at 314-315nm was observed from the gadolinium 8 S 7/2 -6 P 7/2 transition via cathodoluminescence (CL) excitation. The CL-induced intensity was found to be maximum at 9 at% Gd (Y 1.82 Gd 0.18 O 3 ) and an optimized electron probe of V acc = 13 keV was determined for the 1 µm thick thin film. Gadolinium activator saturation was observed for sample current density greater than 0.03 µA/cm 2 . Non-radiative decay via thermal pathways is suspected for the observed activator saturation. Introduction Miniaturized ultraviolet (250 -350 nm) emitting solid-state sources are required as components for proposed device structures such as non-line-of-sight communication transceivers and receivers and bio-particle detection units. Previous work on rare-earth doped yttrium oxide materials have shown emission from the blue to red range of the electromagnetic spectrum from trivalent Pr, Sm, Eu, Tb, Dy, Er, Ho, and Tm [1-2]. We have recently determined that gadolinium-doped yttrium oxide powder exhibits intense emission at~314 -315 nm. In this paper we will report work on gadolinium-doped yttrium oxide (also yttria and yttria sesquioxide) thin films that are being explored as a potential material for thin film solid-state UV device applications. Background and Experimental Gadolinium-doped, yttrium oxide thin films have been prepared by combinatorial sputtering using a radio-frequency magnetron sputtering system (AJA international, ATC 2000 -V). The magnets supporting the sputter targets were operated in an unbalanced mode to maximize the deposition rate. The magnetron system used has a "sputter-up" configuration, where the substrate surface is located above two sputter targets that are tilted and facing the substrate. The sputter guns are spaced 180 o apart in the chamber in reference to the center of the substrate. Hence, the resulting film deposited from this configuration will have a maximum composition gradient along a line on the substrate surface. Gadolinium foil (0.024 in thick, Alfa Aesar) and a yttrium metal target (0.250 in. thick, Kurt J. Lesker), both 99.9% pure, were used as sputtering targets. During deposition, the gadolinium target was operated at 100 W forward power, and the yttrium target was operated at 200 W. The combinatorial film was deposited in a multi-layer fashion; 9 alternating layers, Y 2 O 3 -[Gd -Y 2 O 3 ] 4 were deposited onto Si (001). The Si wafer was 4 in. in diameter, research grade, boron doped, and with 14 -22 Ω-cm resistivity. The total pressure during sputtering was Mat. Res. Soc. Symp. Proc. Vol. 76