快速热退火对ITO薄膜及LED芯片性能的影响

采用金属有机化学气相沉积(MOCVD)技术在蓝宝石衬底上制备了GaN基LED外延层,采用磁控溅射法制备了氧化铟锡(ITO)薄膜,ITO薄膜用于制作与p-GaN的欧姆接触.研究了快速热退火温度为550℃,退火时间为200 s时,不同氧气体积流量对ITO薄膜性能及LED芯片光电性能的影响.结果表明:不通氧气时,ITO薄膜的方块电阻和透过率分别为33 Ω/口和93.1％,LED芯片出现电流拥挤效应,其电光转换效率只有33.3％;氧气体积流量为1 cm3/min时,ITO薄膜的方块电阻和透过率分别为70 Ω/口和95.9％,LED芯片的电流扩展不佳,其正向电压较高,电光转换效率为43.8％;氧气体积流量为0.4 cm3/min时,ITO薄膜的方块电阻和透过率分别为58 Ω/口和95.4％,LED芯片的电流扩展最佳,其亮度最高、正向电压最低,电光转换效率较高,为52.9％.

Effects of Rapid Thermal Annealing on the Performances of ITO Thin Films and LED Chips

GaN based LED epitaxial layers were prepared on sapphire substrates by metal organic chemical vapor deposition (MOCVD) technology.Indium tin oxide (ITO) thin films were deposited by magnetron sputtering method,which were used to make the ohmic contact layer with p-GaN.The effects of different oxygen volume flows on the performance of ITO thin films and photoelectric properties of LED chips were investigated at the rapid thermal annealing temperature of 550 ℃ for 200 s.The results show that without oxygen,the square resistance and the transmittance of ITO thin films are 33 Ω/□ and 93.1％,respectively,and the electro-optical conversion efficiency is as low as 33.3％ due to current crowding effects of the LED chips.When the oxygen volume flow is 1 cm3/min,the square resistance and the transmittance of the ITO films are 70 Ω/□ and 95.9％,respectively.In this case,the current expansion of the LED chips is poor,resulting in high forward voltage,and the electro-optical conversion efficiency is only 43.8％.When the oxygen volume flow is 0.4 cm3/min,the square resistance and the transmittance of the ITO films are 58 Ω/□ and 95.4％,respectively.The current expansion of the LED chips is optimal,and the LED chips have the highest brightness and the lowest forward voltage,resulting in a high electro-optical conversion efficiency of 52.9％.