Polarity Inversion of Ga‐Polar GaN Surfaces by Exposing to Mg and NH₃ in Metal–Organic Vapor Phase Epitaxy

Abstract

A metal–organic vapor phase epitaxy process of polarity inversion (PI) from Ga‐ to N‐polar is reported by exposing the Ga‐polar surface simultaneously to Mg and ammonia flows. This process differs from the conventional Mg heavy‐doping technique by intentionally predepositing a Mg‐rich thin layer on the Ga‐polar surface for PI. A full PI with a smooth surface in the subsequent GaN overgrowth is achieved by an exposure process for 900 s at 700 °C. Atomic force microscopy and piezo‐force microscopy characterizations reveal that the polarity change undergoes simultaneously with pyramid formation after ≈15 nm thick GaN overgrowth. The electron dispersion spectroscopy mapping of Mg indicates high Mg concentrations at the regrowth interface and in the PI domain boundary. A Mg‐rich thin layer is believed to cover the surface after the exposure process and release Mg dopants in the subsequent growth, leading to a high Mg incorporation in the GaN overlayer and therefore inducing PI. P‐type conduction with a hole concentration of ≈2.7 × 1017 cm−3 is achieved in the N‐polar GaN overlayer. It is also demonstrated that such a PI technique can be employed in the growth of a hybrid polarity structured ultraviolet‐light‐emitting diode with a reversed N‐polar contact layer on a Ga‐polar main body.