Unveiling the physics of excellent ohmic contact in Mg-intercalated p-GaN

Abstract

This study investigates the underlying physics responsible for the formation of excellent Ohmic contacts in Mg-intercalated p-type GaN. Through comprehensive analysis of temperature-dependent current–voltage characteristics and electron energy loss spectroscopy (EELS), several previously unreported phenomena are identified. Key findings include a significant reduction in barrier height, enhanced hole concentration with increasing annealing temperature, and a transition from mixed conduction mechanisms to direct tunneling dominance in samples annealed at 550 °C or above. EELS measurements further confirm bandgap narrowing in Mg-intercalated GaN. These results are coherently explained by the formation of a two-dimensional Mg-intercalated superlattice, which induces strong internal polarization fields and elastic strain. These results give rise to four effects: (i) reduced barrier height, (ii) narrowed barrier width, (iii) enhanced hole generation, and (iv) a shallower Mg acceptor level that also functions as a trap center facilitating Poole–Frenkel emission and trap-assisted tunneling. Collectively, these effects promote direct tunneling, resulting in a significant reduction in contact resistance. This work provides new physical insights into the role of Mg intercalation, offering a promising pathway toward the development of high-performance GaN-based optoelectronic and power devices.