Improved device isolation in AlGaN/GaN HEMTs on Si by heavy Kr+ Ion implantation

Abstract

GaN high-electron-mobility transistor (HEMT) based technology demonstrated excellent high-frequency, high microwave power and power switching device applications that exceeded the existing Si technology limits. Inter device isolation of GaN-based HEMTs are typically achieved with either plasma mesa etching or ion implantation. The advantage for the ion implantation-based isolation approach is that it can offer device planarity and thus improve the fabrication yield. In addition, the planarity will avoid the gate from touching the 2DEG channel at the mesa-sidewall thus reduces the gate leakage current. For device isolation, different ion species (N+, O+, Ar+, Fe+ and Zn+) have been utilized for AlGaN/GaN HEMTs [1-5]. Except Fe+, no ion species have been proven to maintain the high resistivity of the the GaN buffer layer after high-temperature annealing. Recently, Umeda et al. reported thermally stable device isolation by Fe+ implantation [5]. However, Fe+-ions may create deep levels. In this work, we have selected inert Kr+-ions which can provide heavy damage to the crystal lattice. As Kr+ has ~2×, ~1.5× and 1.2× heavier atomic mass than Ar+, Fe+, and Zn+ ions, respectively. it is expected that the heavy Kr+-ion induced lattice damages/disorders will be hard to recover completely by high-temperature thermal annealing. To investigate the thermal stability of Kr+ implant-isolation, we have investigated thermal stability of implant-isolated samples by isochronal annealing process. To-date, there are also very few reports on the effect of the blocking voltage of implant-isolated AlGaN/GaN HEMT structures with SiN passivation [2], which has significant impact on their high breakdown voltage characteristics. Hence, in this work, we have also investigated the influence of SiN passivation in the device isolation current (i.e. buffer leakage current, Ibuff) on implant-isolated and mesa-isolated devices.