中文摘要：

硅衬底GaN基发光二极管（LED）的内置n型欧姆接触在晶圆键合时的高温过程中常常退化，严重影响LED的工作电压等器件性能.本文深入研究了内置n电极蒸镀前对n-GaN表面的等离子体处理工艺对硅衬底GaN基发光二极管n型欧姆接触特性的影响.实验结果表明，1.1 mm×1.1 mm的LED芯片在350 mA电流下，n-GaN表面未做等离子体处理时，n电极为高反射率Cr/Al的芯片正向电压为3.43 V，比n电极为Cr的芯片正向电压高0.28 V.n-GaN表面经O2等离子体表面处理后，Cr/Al和Cr电极芯片的正向电压均有所降低，但Cr/Al电极芯片的正向电压仍比Cr电极芯片高0.14 V.n-GaN表面经Ar等离子体处理后，Cr/Al电极芯片正向电压降至Cr电极芯片的正向电压，均为2.92 V.利用X射线光电子能谱对Ar等离子体处理前后的n-GaN表面进行分析发现，Ar等离子体处理增加了n-GaN表面的N空位（施主）浓度，更多的N空位可以提高n型欧姆接触的热稳定性，缓解晶圆键合的高温过程对n型欧姆接触特性的破坏.同时还发现，经过Ar等离子体处理并用HCl清洗后，n-GaN表面的O原子含量略有增加，但其存在形式由以介电材料GaOx为主转变为导电材料GaOxN1-x和介电材料GaOx含量相当的状态，这会使得接触电阻进一步降低.上述两方面的变化均有利于降低LED芯片的正向电压.

英文摘要：

Unlike the finger-like n-contact that is prepared after the wafer bonding and the N-polar GaN surface roughening for GaN-based vertical structure light-emitting diodes （LEDs） grown on Si substrates, the embedded via-like n-contact is formed prior to the wafer bonding. The high temperature process of the wafer bonding often causes the electrical characteristics of the via-like embedded n-contact to degrade. In this paper, we study in detail the effect of plasma treatment of the n-GaN surface on the forward voltage of GaN-based LED grown on Si substrate. It is shown that with no plasma treatment on the n-GaN surface, the forward voltage （at 350 mA） of the 1.1 mm×1.1 mm chip with a highly reflective electrode of Cr （1.1 nm）/Al is 3.43 V, which is 0.28 V higher than that of the chip with a pure Cr-based electrode. The LED forward voltages for both kinds of n-contacts can be reduced by an O2 plasma treatment on the n-GaN surface. But the LED forward voltage with a Cr/Al-based electrode is still 0.14 V higher than that of the chips with a pure Cr-based electrode. However, after an Ar plasma treatment on the n-GaN surface, the LED forward voltage with a Cr/Al-based electrode is reduced to 2.92 V, which is equal to that of the chip with a pure Cr-based electrode. The process window of the n-GaN surface after the Ar plasma treatment is broader. X-ray photoelectron spectroscopy is used to help elucidate the mechanism. It is found that Ar plasma treatment can increase the concentration of N-vacancies （VN） at the n-GaN surface. VN acts as donors, and higher VN helps improve the thermal stability of n-contact because it alleviates the degradation of the n-contact characteristics caused by the high temperature wafer bonding process. It is also found that the O content increases slightly after the Ar plasma treatment and HCl cleaning. The O atoms are mainly present in the dielectric GaOx film before the Ar plasma treatment and the HCl cleaning, and they exist almost equivalently in the conductive GaOxN1-x film