Control of Polarity of AlN Grown on Sapphire Substrate and Growth with Both Al‐ and N‐Polarities

Abstract

AlN with both Al‐ and N‐polarities in the c‐axis direction has attracted attention as a second‐harmonic generation device with a quasi‐phase‐matching structure in the ultraviolet wavelength region. Herein, N‐polar AlN on patterned AlN is regrown by metal–organic vapor‐phase epitaxy, and AlN lateral polar structures (LPSs) are fabricated without the simultaneous growth of Al‐ and N‐polar AlN layers. A 1 μm thick Al‐polar AlN layer is grown on sapphire, followed by the fabrication of a striped pattern. Subsequently, N‐polar AlN is regrown on an exposed sapphire substrate. In the first experiment, the sidewalls after reactive ion etching are not vertical, and voids are formed when N‐polar AlN is regrown. KOH wet etching is performed to overcome this problem and improve the verticality of sidewalls. Consequently, a perfect AlN LPS with a minimum period of 2 μm is fabricated. The verticality of the sidewalls in the LPS and the regrowth conditions of N‐polar AlN with a very low V/III ratio are crucial to the fabrication of AlN LPSs with highly vertical interfaces.