Determination of the optical energy gap of Ge1−xSnx alloys with 00.14 (original) (raw)

Determination of the optical energy gap of Ge[sub 1−x]Sn[sub x] alloys with 0<x<0.14

Applied Physics Letters, 2004

The optical energy gap of Ge 1Ϫx Sn x alloys has been determined from transmittance measurements, using a fast-Fourier-transform infrared interferometer. Our results show that the change from indirect to direct band gap occurs at a lower critical Sn concentration (x c ) than the value predicted from the virtual crystal approximation, tight binding, and pseudopotential models. However, a close agreement between the experimental results and the predictions with deformation potential theory is observed. The concentration x c , which is theoretically expected to be 0.09, actually it is observed to lie between 0.10Ͻx c Ͻ0.13.

Nonlinear behavior of the energy gap in Ge[sub 1−x]Sn[sub x] alloys at 4 K

Applied Physics Letters, 2007

The optical energy gap of Ge 1−x Sn x alloys ͑x ഛ 0.14͒ grown on Ge substrates has been determined by performing transmittance measurements at 4 K using a fast fourier transform infrared interferometer. The direct energy gap transitions in Ge 1−x Sn x alloys behave following a nonlinear dependence on the Sn concentration, expressed by a quadratic equation, with a so called bowing parameter b 0 that describes the deviation from a simple linear dependence. Our observations resulted in b 0 RT = 2.30± 0.10 eV and b 0 4 K = 2.84± 0.15 eV, at room temperature and 4 K, respectively. The validity of our fit is limited for Sn concentrations lower than 15%.