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EL signal from the Ge and GeSn diode devices compared with room temperature PL spectra from similarly grown Ge and GeSn layers. For the EL spectra, the current density was for the Ge device and for the GeSn device. The PL spectra were obtained under 980 nm laser excitation. The relative scale of all spectra is arbitrary. The main emission peak is assigned to direct gap transitions in all spectra.
(Left) Electroluminescence spectra from a Si/Ge heterostructure diode as a function of the injection current density. (Right) Electroluminescence spectra from a heterostructure diode as a function of the injection current density. The successive spectra have been shifted vertically for easy visualization. The solid lines represent a fit with Eq. (1). All spectra were fit simultaneously using a single normalization parameter. An even better fit of the high-energy tail of the spectra can be obtained if the fit parameters are allowed to vary slightly for the different injection currents.
Experimental electroluminescence peak intensities (markers) and corresponding theoretical predictions (lines) based on Eq. (1). The different emission intensities from the two samples are explained by their different thicknesses as well as by their different electron-hole concentrations at a given injection current.
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