Molecular beam epitaxy, photoluminescence from Mn²⁺ multiplets and self-trapped exciton states of γ-MnTe single-crystalline thin films

Single-crystalline γ-MnTe thin films with zinc-blende structure were grown epitaxially on InP(1 1 1) by molecular beam epitaxy. Two-dimensional growth regime and atomic surface flatness are achieved, and appearance of Laue's oscillation peaks illustrates the superior crystalline quality and interface of γ-MnTe films. A pseudocrystal buffer layer is formed at interface releasing the strain led by the large lattice mismatch between γ-MnTe and InP, and then growth of γ-MnTe films with a perfect lattice evidences the high-quality crystallinity in a fully relaxed state. Photoluminescence (PL) emissions from ⁴T_1g(⁴G) and ⁴T₁(⁴G) related to Mn²⁺ ions d-d multiplets are observed with their respective activation energies of ∼142.5 meV and ∼323.5 meV. Such high potentials reflecting the nonradiative recombination indicate the thermal stability of these PL. Moreover, two extra PL transitions assigned to be the emissions from self-trapped exciton (STE) states are found below T_N. Time-resolved PL (TRPL) spectra at various temperatures indicate that the relaxation dynamics of photoexcited d-electrons is strongly correlated to the antiferromagnetic ordering transition due to the synergy of magnon, phonon and STE states. These findings suggest that introduction of STE states in a material by controlling its magnetic ordering qualifies the competition in optoelectronics devices.