The effects of rapid thermal process on the properties of sputtered SrS:CeF3 thin films

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Abstract
A Y2O3/SrS:Ce/BaTiO3 electroluminescent (EL) structure has been deposited by rf-magnetron reactive sputtering and, subsequently, submitted to various thermal treatments. The effects of the rapid thermal process (RTP) on the properties of SrS:Ce thin films have been investigated, and compared with the results obtained by the conventional furnace. After postdeposition annealing, the SrS film has the tendency to recrystallize preferentially in the (200) plane. The higher RTP temperature also results in the larger grain size of SrS. Auger measurements show that the RTP method can overcome the nonstoichiometry and interdiffusion problems encountered in the furnace-treated sample. It was found that the EL peaks gradually recovered to the band transitions of Ce3+ ions (475 and 530 nm) in the SrS crystal field as the RTP temperature increased from 650 to 850 °C. The threshold voltage can be further reduced to 150 V, and the brightness increases to eight times, as compared with that of the optimum furnace-treated device. The improvements in EL performance are owing to the facts that the RTP can enhance the crystallinity of SrS, alleviate oxygen-induced defect centers from interdiffusion, activate Ce3+ ions in phosphor, and yield a blueshift in emission colors.