(Invited) Prospects for Magnesium Diffusion Doping of GaN

Abstract

Ex-situ p-type doping of GaN has been a long-standing challenge and prevented adoption of numerous devices. While regrowth of p-GaN on etched surfaces and ion implantation have made progress, technical challenges remain. Diffusion of Mg into GaN has received considerably less attention, primarily due to the extremely low diffusivity of Mg in GaN as well as the instability of GaN at the temperatures required (typically >1000oC), as well as its propensity to form compensating defects. Recent work at LLNL on GaN grown both on sapphire and n-type GaN substrates has demonstrated the potential for diffusion of Mg at temperatures as low as 700oC. This is theorized to be through enhanced formation of Gallium vacancies, which provide a pathway for rapid diffusion into GaN. Use of a solid Mg source, such as MgF2, capped by a metal has been shown to be effective, with the diffusivity dependent on the specific metal cap (Figure 1).This talk will discuss the chemical thermodynamics of this process, termed Gallidation Assisted Impurity Diffusion or GAID, methods for control, current challenges, and device results including enhanced barrier height Schottky contacts resulting from the process. Prospects for the future of the technique and its applicability to new device concepts will be briefly addressed.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, LLNL-ABS-821793. This support does not constitute an express or implied endorsement on the part of the Government. The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, PNDIODES program monitored by Dr. Isik Kizilyalli. Figure 1