Luminescence Studies of Indirect-Bandgap Layered BN Polytypes

Abstract

  Hexagonal boron nitride (hBN) is a semiconductor that crystallizes in layers of a two-dimensional honeycomb structure composed of sp²-bonded B and N, namely monolayer BN (mBN), which are connected by out-of-plane π bond with a stacking sequence AA'. Since hBN exhibits high quantum efficiency (QE) near-band-edge emission at around 5.77 eV (215 nm) in spite of the indirect bandgap, hBN has attracted attention as a novel deep-ultraviolet (DUV) light-emitting material. Recently, syntheses and characterizations of layered BN polytypes such as AB-stacked graphitic BN (bBN), ABC-stacked rhombohedral BN (rBN), and even mBN have been reported, which included important information with respect to both scientific research and the practical use. In this article, the results of steady-state, temporary resolved, and spatially resolved luminescence measurements on hBN microcrystals and rBN epilayers containing bBN segments are shown to explore the superiority of hBN polytypes. Similar to the case of hBN, rBN and bBN exhibit excellent light-emitting performances in spite of principally indirect bandgap, including the retrograde thermal quenching behavior.