(Invited) Advances in Ion Implantation of GaN and AlN

Abstract

Ion implantation is one of the basic tools for semiconductor device fabrication and as such any maturing semiconductor system should be capable of being processed in this form. Currently, III-nitrides dot not possess a robust ion implantation toolbox that allows for reliable implantation control and activation, thus precluding the possibility of pursuing advanced device architectures comparable to those in SiC. This is obvious when trying to advance the capabilities of the III-nitrides for power applications, where the need for proper field managing schemes require spatially distributed doping distributions that can be achieved by ion implantation. Recent advances in ion implantation for the realization n-type AlN and p-type GaN will be discussed. AlN is considered for deep-UV optoelectronics and next generation high power devices due to its ultra wide bandgap. So far, n-type AlN has been achieved by doping with silicon during epitaxial growth. However, achieving high conductivity in n-type AlN is still a major challenge due to self-compensation via DX and vacancy complex formation at equilibrium. This has made it necessary to consider other non-equilibrium based doping methods, such as ion implantation. In this work, doping AlN by Si implantation is considered. Si implantation was realized into AlN homoepitaxial films grown on bulk AlN substrates via metal organic chemical vapor deposition (MOCVD). Samples were implanted with doses ranging between 5x1013and 1x1015cm-2at 100 keV at RT. Although high-temperature annealing is necessary for damage removal, it enables compensating defect formation by vacancy-silicon complex formation favorable at equilibrium as observed in MOCVD grown AlN. Hence point defect control is necessary during annealing. We further demonstrate defect quasi Fermi level (dQFL) control based compensating point defect reduction in Si implanted AlN during damage recovery. Thus, the highest reported n-type conductivity in AlN was achieved. These results show a possible pathway for the realization of n-type AlN for future optoelectronic and power electronic devices. GaN-based high power switches are a promising avenue towards realizing advances in power management. Controlling the selective area doping of both n- and p-type regions is necessary to realize these device structures. Although high n-type carrier concentrations and conductivities in GaN have been reproducibly demonstrated, achieving high p-type conductivity after ion implantation remains a challenge. To prevent the surface decomposition during annealing at these elevated temperatures required for post-implantation anneals, previous efforts have focused on the use of capping layers (e.g. AlN) and/or complicated annealing procedures. In this work we demonstrate the ability to successfully achieve p-type conductivity in GaN films via room temperature Mg implantation and a post-implantation annealing procedure at high pressure (1 GPa). The highest recorded p-type conductivity (~0.1 Ω-1·cm-1) was measured on the Mg implanted GaN film grown on a sapphire substrate and annealed at 1300 °C and 1 GPa. The implantation and annealing conditions that resulted in the highest p-type conductivity were selected to fabricate p-i-njunction diodes by Mg implantation in n-type GaN grown homoepitaxially on Ammono wafers. All these results support the possibility of realizing successful ion implantation in III-nitrides adding to the growing toolbox of capabilities for this technology.