Double‐Polarity Selective‐Area Growth of GaN by Metal‐Organic Vapor‐Phase Epitaxy Using Narrow‐Pitch Patterns

Abstract

GaN films are prepared via double‐polarity selective‐area growth (DP‐SAG) using metal‐organic vapor‐phase epitaxy. Here, we demonstrate an improved DP‐SAG process using a carbon mask and an initial Ga‐polar GaN layer to fabricate a GaN film consisting of periodic Ga‐polar and N‐polar domains. The GaN films with periodically poled structures (alternating Ga‐polar and N‐polar regions) can serve as quasi‐phase‐matching (QPM) crystals in second‐harmonic generation (SHG) devices for ultraviolet laser applications. Deposition of the initial Ga‐polar GaN layer allows the employment of a wider range of growth conditions (e.g., growth rate), while preventing the lateral overgrowth of N‐polar GaN domains on the Ga‐polar GaN ones. The pitch of the pattern is successfully decreased from 120 μm used previously by our group to a narrower one of 20 μm, as confirmed by scanning probe microscopy. Moreover, thick Ga‐polar GaN layers with sharp hetero‐interfaces and a surface potential difference of ≈100 mV can be achieved using a 20‐μm‐pitch pattern. The method proposed in this report is useful for the fabrication of a QPM crystal for UV SHG devices with sharp hetero‐interfaces.