Effects of Electron-Beam Evaporated ITO Films on Performance of AlGaInP Light-Emitting Diodes

• Main Authors: Jun Chang, 張閏
• Other Authors: 武東星
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/22047856057762440360

碩士 === 國立中興大學 === 精密工程學系所 === 94 === Abstract Although III-V light-emitting diodes（LEDs）have been developed for several years, there still exist some problems to be solved, such as the luminescence efficiency and the watt-per-dollar issue. The use of indium-tin oxide（ITO）thin films as the transparent current-spreading layer (TCL) has become an important approach to improve the external quantum efficiency. Currently, the electron-beam evaporation method is widely used in the ITO process line for AlGaInP LEDs because of its mass production capability. However, it is very difficult to precise control the ITO stoichiometric and film quality using an electron-beam evaporator. In this thesis, transmittance and specific resistance of the ITO films were investigated as functions of the oxygen flow and evaporation rates during the deposition process. It was found that a minimum reflectance at 575 nm of ITO can be achieved with an ITO thickness of 250 nm. A suitable thickness of ITO thin film will improve the luminescence efficiency decrease the forward voltages of AlGaInP LEDs from 0.03 to 0.5 V. After the rapid thermal annealing treatment, the lowest reflection wavelength of ITO showed a red shift of 5~10 nm due to the recrystallization effect. In our experimental range, the deposition rate was confirmed to change the grain size of the ITO thin film. However, there is no evident effect on the light output power and electrical properties of the ITO/AlGaInP LEDs. On the other hand, the oxygen partial pressure during the electron-beam evaporation process plays an important role in determining the LED performance. If the oxygen partial pressure is too low, the ITO film will degrade to a metallic property and shows a transmittance down to 70%. Finally, the ITO/AlGaInP LEDs show a maximum luminance and minimum forward voltage with an oxygen flow of 13 and 5 sccm, respectively. The results indicate the deposition parameters of the ITO TCLs should be compromised in order to achieve high performance AlGaInP LEDs .