Thin film electroluminescent (EL) structure of Y2O3/SrS:Ce/BaTiO3 has been deposited by rf-magnetron reactive sputtering and subsequently submitted to various thermal treatments. The effects of rapid thermal process (RTP) on the structural and EL characteristics of SrS:Ce thin films have been investigated, and compared with the results obtained by the conventional furnace. After the post-deposition 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 eight times as much as the optimum furnace-treated device. The improvements in EL performance are due 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 blue shift in emission colors.
- Heat treatment
- Optical properties