AlGaInP與GaN發光二極體之特性提升

Abstract

本研究為改善四元發光二極體與金屬反射層之特性，使用晶圓接合技術將LED磊晶層轉移至SiC基板並配合金屬反射層與表面粗化方式增加光的取出與焦耳熱之問題。在20mA電流驅動下比傳統發光二極體提升了4倍發光強度，飽合電流也提升了4倍。由於接合金屬中In會有擴散之問題，於是使用Ti/Pt/Au作為擴散阻擋層，使用Auger分析可發現Ti/Pt/Au防止了In之擴散。 另一部份，使用Ag作為金屬反射層。由於Ag退火會有氧化與表面聚集使反射率下降，實驗中添加了Ni當阻擋層。最後證實了Ni之添加可有效防止Ag氧化使反射率仍然維持90%，並將此系統沉積於GaN在470nm量測其反射率仍有90~100%。

In this thesis, the AlGaInP epi layer was transferred successfully from GaAs to SiC substrate by wafer bonding technology at first. Then the light-extraction efficiency was also increased by surface roughening and new metal reflector.

The results of the experiments showed that the saturation current of SiC-light emitting diodes (LEDs) was increased. Therefore, the issue of joule-heat effect was solved by using SiC substrates instead of GaAs substrates, because of the better heat conduction SiC substrates have.

The improvement of the light-extraction efficiency was due to the surface roughening and new metal reflector. As the light driven by multi-quantum well passed through the boundary of air and LEDs, the rougher surface can decreased the probability of the total reflection. Therefore, the light-extraction efficiency was improved.

Because of the high reflectivity, the Ag metal was chosen to replace the BeAu alloy for reflector in the next experiments. The results of experiments also showed that the light intensity of LEDs was enhanced by using Ag reflector. The light intensity of SiC-LEDs withAg reflector and surface roughening was 4 times than that of general GaAs-LEDs at the injection current of 20mA.

However, there are still some issues for using Ag reflector. The advance analyses showed that heating process might cause the agglomeration of Ag reflector and the diffusion of indium atoms. These phenomenons decreased the reflectivity of the Ag reflector. Therefore, the diffusion barrier layer (Ti/Pt/Au) and Ni thin film were used in the structure of LEDs to solve these issues. Finally, the reflectivity of the Ag reflector was enhanced as high as ~90% by means of the new scheme, even after annealing at 270℃ for 1 hour.