Compositional dependence of optical critical point parameters in pseudomorphic GeSn alloys

Abstract

Spectroscopic ellipsometry was used to investigate the optical response of pseudomorphic Ge 1Àx Sn x (0 x 0.17) alloys grown directly on Ge (100) by molecular beam epitaxy. A detailed compositional study of amplitudes, broadenings, energies, and phase angles associated with critical points E 1 , E 1 þ D 1 , E 0 0 , and E 2 of GeSn alloys was carried out using a derivative analysis. The results can be understood in terms of the electronic bandstructure of Ge or relaxed GeSn alloys with the following differences. First, broadening parameters in pseudomorphic alloys are found to have lower values compared to relaxed alloys indicating lower dislocation density in our pseudomorphic alloys relative to relaxed alloys. Second, the amplitudes of E 1 and E 1 þ D 1 are enhanced and reduced, respectively, with respect to relaxed GeSn alloys, and the trends are captured using the k.p method as a biaxial stress induced effect. Third, phase angles are lower than Ge for all the critical points suggesting reduction of excitonic effects in GeSn with respect to Ge.

Mid-infrared to ultraviolet optical properties of InSb grown on GaAs by molecular beam epitaxy

“…This might be attributed to the presence of threading dislocations and small compressive strain in the nearly relaxed films. 27,30 The phase angles for E 1 and E 1 þ D 1 obtained for the film are in good agreement with the bulk values. We notice that the magnitude of phase angle for E 1 is slightly greater than that for E 1 þ D 1 for both our film and bulk, consistent with the finding for bulk InSb 11 at room temperature.…”

Numerical calculation of strain-N+-Ge1−xSnx/P+-δGe1−xSnx/N−-Ge1−y−zSiySnz/P+-Ge1−y−zSiySnzheterojunction tunnel field-effect transistor

“…36,37) In these simulations, direct tunneling at the Γ valley rate is several orders higher than that of the phonon-assisted indirect L valley tunneling, and so direct tunneling is the dominant tunneling process. 38,39) According to the tunneling theory mentioned above, the relationship between the BTBT direct generation rate G dir and the electric field F is…”

“…As mentioned above, the thin Ge 1−x Sn x layer grown on a Ge substrate will suffer compressive strain. Hence, the compressive strain properties of Ge 1−x Sn x should be considered because they lower the Ge 1−x Sn x light hole band, 39) which affects the value of E À tunnel . On the basis of the material band structures and effective masses in Sect.…”

Achieving enhanced hole transport capability of Ge1−xSnxalloys through uniaxial compressive strain

“…Recently, germanium-tin (Ge 1−x Sn x ) alloys are attracting a great deal of attention due to the tunable band gaps. [1][2][3][4][5] The Ge 1−x Sn x alloys may transit from indirect gap to direct gap when the Sn composition x exceeds the critical point x c . 5) The direct gap properties of Ge 1−x Sn x alloys are beneficial for the corresponding optoelectronic devices.…”