A novel wet etching method for AlGaN/GaN heterojunction structures is proposed using thermal oxidation f ollowed by wet etching in KOH solution.It is found that an AlGaN/GaN heterostructure after high temperature oxidation above 700℃could be etched off in a homothermal（70℃） KOH solution while the KOH solution had no etching effects on the region of the AlGaN/GaN heterostructure protected by a SiO_2 layer during the oxidation process.A groove structure with 150 nm step depth on an AlGaN/GaN heterostructure was formed after 8 h thermal oxidation at 900℃followed by 30 min treatment in 70℃KOH solution.As the oxidation time increases,the etching depth approaches saturation and the roughness of the etched surface becomes much better.The physical mechanism of this phenomenon is also discussed.
In this article, a detailed analysis of the wet- etching technique for AIGaN/GaN heterostructure using dry thermal oxidation followed by a wet alkali etching was performed. The experimental results show that the oxida- tion plays a key role in the wet-etching method and the etching depth is mainly determined by the oxidation tem- perature and time. The correlation of etching roughness with oxidation time and temperature was investigated. It is found that there exists a critical oxidation temperature in the oxidation process. Finally, a physical explanation of the oxidation procedure for A1GaN layer was given.
Yang LiuJin-Yan WangZhe XuJin-Bao CaiMao-Jun WangMin YuBing XieWen-Gang
Semi-on DC stress experiments were conducted on A1GaN/GaN high electron mobility transistors （HEMTs） to find the degradation mechanisms during stress. A positive shift in threshold voltage （VT） and an increase in drain series resistance （RD） were observed after semi-on DC stress on the tested HEMTs. It was found that there exists a close correlation between the degree of drain current degradation and the variation in VT and RD. Our analysis shows that the variation in Vx is the main factor leading to the degradation of saturation drain current （IDs）, while the increase in RD results in the initial degradation of Ios in linear region in the initial several hours stress time and then the degradation of VT plays more important role. Based on brief analysis, the electron trapping effect induced by gate leakage and the hot electron effect are ascribed to the degradation of drain current during semi-on DC stress. We suggest that electrons in the gate current captured by the traps in the A1GaN layer under the gate metal result in the positive shift in VT and the trapping effect in the gate-drain access region induced by the hot electron effect accounts for the increase in RD.
