Enabling thin p-GaN Ohmic contacts through ultrathin magnesium deposition and brief thermal annealing

Gallium nitride (GaN) is a key semiconductor for optoelectronic and power electronic applications. However, achieving low-resistance Ohmic contacts to p-GaN remains challenging, particularly after plasma processing. Annealing of metallic magnesium (Mg) film on p-GaN has emerged as a promising approach, but severe surface roughening limits its applicability to thin (<100 nm) p-GaN layers widely used in practical devices. Here, we demonstrate a capless ultrathin (<10 nm) Mg deposition followed by a soft anneal (600 °C, 300 s) that forms a smooth, ultra-shallow, heavily acceptor-doped surface layer. The process maintains surface smoothness while achieving a low specific contact resistivity of (1–3) × 10−4 Ω cm2 at zero-bias with linear I–V characteristics, even on plasma-etched surfaces. Quasi-vertical p–i–n diodes fabricated using this approach exhibit low leakage currents and high breakdown voltages, indicating preserved junction integrity. This work provides a practical and scalable strategy for forming robust Ohmic contacts on thin p-GaN, with broad implications for GaN-based electronic and optoelectronic devices.