Ag/p-GaN欧姆接触的图形化及表面处理工艺研究

Research on Patterning and Surface Treatment Process of Ag/p-GaN Ohmic Contact

摘要:

Ag在可见光范围内具有极高的反射率且具有低的接触接触电阻率,特别适合LED应用。但是Ag与p-GaN的粘附性较差,不利于该工艺的产业化应用。本论文研究了Ag/p-GaN欧姆接触的工艺,得到较为优化的工艺方法并应用于器件制备。文章研究了直接剥离Ag、氧等离子体去底胶后剥离Ag和湿法腐蚀Ag三种工艺制备Ag图形,对比了三种工艺样品的粘附性及接触电性,发现直接剥离Ag工艺欧姆存在Ag脱落问题,去底胶后剥离Ag工艺无法形成欧姆接触,而腐蚀后退火的样品则可以实现较好的粘附和较佳电性；通过XPS分析了不同工艺对接触特性影响的机理。进一步,对比优化了Ag蒸发前表面化学处理工艺,结果表明酸性溶液处理或碱性溶液可以有效降低欧姆接触电阻率,酸性溶液处理略优。优化后的欧姆接触工艺可应用于可见光及深紫外LED器件制备,器件电学性能如下：在40 A/cm2^{电流密度下},蓝色发光二极管电压为2.95 V,紫外发光二极管电压为6.01 V。

Abstract:

Ag is a desirable ohmic contact metal on p-GaN due to its low contact resistivity on p-GaN and high reflectivity in the visible spectrum. However, the poor adhesion of Ag layer on p-GaN hinder its mass production application. In this work, the influences of the process conditions on Ag/p-GaN ohmic contact have been studied. An optimized process was obtained and applied in the fabrication of devices. Ag patterns were prepared by three kinds of processes: direct lift-off, lift-off after an oxygen plasma treatment, and wet etching. The adhesive and electrical properties of the samples which were fabricated by the three kinds of processes were compared. It was found that the Ag layer is easy to peel off after direct lift-off process, and the ohmic contact could not be formed after an oxygen plasma treatment. In contrast, the wet-etch samples showed better adhesion and electrical properties after annealing. The mechanism of the influences of different processes on the contact performances were analyzed by X-ray photoelectron spectroscopy. Furtherly, surface chemical treatments before Ag deposition were compared and optimized. The results showed that acidic or alkaline solution treatment could effectively reduce ohmic contact resistivity, and the effect of acidic solution treatment was slightly better. The optimized ohmic contact process can be applied to fabricate the visible light and deep ultraviolet (DUV) LED devices. At 40 A/cm2 current, the voltages of the fabricated blue LEDs and DUV LEDs were 2.95V and 6.01 V, respectively.