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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 4K. All the absorption spectra exhibit well-defined zero phonon lines (ZPL) at 11395cm−1 (1.41eV) and 11902cm−1 (1.48eV) 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 Mn2+ 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 55cm–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. [Copyright &y& Elsevier]

Abstract: The growth of self-organized dots of Mn-doped GaN on AlN by plasma-assisted molecular beam epitaxy was studied. The observations of reflection high-energy electron diffraction (RHEED) revealed that the transition of the growth mode from 2D to 3D was delayed by adding a small amount of Mn flux and it disappeared with the further increase in Mn flux. By atomic force microscope (AFM) measurement on a surface with uncapped dots, it was found that the 2D–3D transition occurs with the formation of high dots density only when a tiny amount of Mn flux was added. A possible mechanism for the suppression of the dot formation by additional Mn atoms is discussed. [Copyright &y& Elsevier]

Abstract: Raman spectroscopy has been used to study the lattice properties of plasma-assisted molecular beam epitaxy grown GaN:Mn layers (0–18% Mn). Raman spectra corresponding to the intrinsic GaN layers demonstrate three Raman active excitations at 144, 570 and 729.2cm−1, identified as , and A1(LO) respectively. The Mn-doped GaN layers exhibit additional excitations attributed to defect-activated Raman scattering and Mn m –N (m =1–4) related frequency modes in the vicinity of mode. Subsequently, detailed X-ray diffraction measurements have revealed the coexistence of cubic phases in the predominantly hexagonal GaN lattice. [Copyright &y& Elsevier]