High-resolution spectroscopic investigation of the Mn centre in GaN

Abstract

A set of molecular-beam-epitaxy grown GaN:Mn films with Mn concentration from 0.03 to 5.7% was investigated by Fourier transform infrared absorption at 4 K. All the absorption spectra exhibit well-defined zero phonon lines (ZPL) at 11395 cm −1 (1.41 eV) and 11902 cm −1 (1.48 eV) and a series of phonon replicas at higher energy. The position, linewidth and integrated area of the main absorption features were analyzed versus the manganese concentration. The integrated optical cross section of the main ZPL is of 8.6×10 −16 cm/Mn, that is three orders of magnitude larger than that for Cr in II–VI semiconductors, and the intensity of the phonon-related absorption cross section is of the same order of magnitude as the ZPL. This low electron–phonon coupling suggests a delocalized hole weakly bound to the Mn 2+ ions, similar to Mn in GaAs, in contradiction with the high ionization energy. For Mn-concentration higher than 1% the integrated absorption decreases, attributed to the incorporation of Mn in non-isolated and substitutional sites, or compensated by donor growth defects. Linewidth of the main ZPL increases from 11.6 to 55 cm –1 for Mn-concentration increasing from 0.03% to 5.7%. The analysis of these absorption features indicated a peculiar behaviour of Mn in GaN compared to similar impurities in other semiconductors: it has a low electron–phonon coupling such as the shallow impurity Mn in GaAs, and a high ionization energy such as Cr in II–VI materials.