Investigation of hydrogen inductively coupled plasma treatment effect for Ge_0.938Sn_0.062/Ge/Si film using photoreflectance spectroscopy

Temperature-dependent photoreflectance (PR) measurements for Ge_0.938Sn_0.062/Ge/Si films treated with a hydrogen inductively coupled plasma (H₂-ICP) have been performed. The Ge_0.938Sn_0.062 film is grown on Ge-buffered Si substrate by ultra-high vacuum chemical vapor deposition method, and the H₂-ICP treatment was carried out for 5 min for the Ge_0.938Sn_0.062 epitaxial layer. The high-resolution X-ray diffraction results show that the compressive strain of the Ge_0.938Sn_0.062 layer decreases and the tensile strain of the Ge buffer layer increases after H₂-ICP treatment. The PR spectrum of as-grown Ge_0.938Sn_0.062/Ge/Si film at 300 K consists of three signals at 0.603, 0.782 and 0.814 eV, which are assigned to the direct transitions from conduction Γ valley to the valence bands related to the surface of Ge_0.938Sn_0.062, the Ge/Si and GeSn/Ge interfaces, respectively. After H₂-ICP treatment, two PR signals of 0.604 and 0.781 eV were obtained at 300 K and they are attributed to the direct transition energies of the Ge_0.938Sn_0.062 and the Ge buffer layer, respectively. As temperature decreases, new weak PR signals appear in the lower energy regions of both PR signals from the H₂-ICP treated GeSn and Ge layers at 210 K and 130 K, respectively, due to the increase of tensile strain in Ge layer while no new signal appears for the as-grown sample. The PR spectrum of the H₂-ICP treated sample at 10 K shows four signals, and these signals are assigned to the surface of GeSn and GeSn at the interface between GeSn and Ge buffer layers, the Ge at the interface between GeSn and Ge buffer layers, and the Ge at the interface between Ge buffer layer and Si substrate, respectively. These PR results indicate that H₂-ICP treatment significantly affects the strain and defects near the interface between GeSn and Ge layers, and thus optical properties of GeSn layer are also altered by H₂-ICP treatment.