Abstract
We present results on CVD growth and electro-optical characterization of Ge(0.92)Sn(0.08)/Ge p-i-n heterostructure diodes. The suitability of Ge as barriers for direct bandgap GeSn active layers in different LED geometries, such as double heterostructures and multi quantum wells is discussed based on electroluminescence data. Theoretical calculations by effective mass and 6 band k∙p method reveal low barrier heights for this specific structure. Best configurations offer only a maximum barrier height for electrons of about 40 meV at the Γ point at room temperature (e.g. 300 K), evidently insufficient for proper light emitting devices. An alternative solution using SiGeSn as barrier material is introduced, which provides appropriate band alignment for both electrons and holes resulting in efficient confinement in direct bandgap GeSn wells. Finally, epitaxial growth of such a complete SiGeSn/GeSn/SiGeSn double heterostructure including doping is shown.
Highlights
Group-IV light sources based on direct bandgap GeSn and indirect bandgap SiGeSn alloys, which can be monolithically integrated on silicon, receive rising attention currently
We demonstrate that multi quantum wells (MQWs) heterostructures with direct bandgap GeSn wells, type I alignment for both L and Γ- valleys and reasonable barrier-well offsets can be obtained in {SiGeSn/GeSn} MQWs
We have presented the growth and electro-optical characterization of both p-i-n GeSn homojunction and {GeSn/Ge} MQW Light emitting diodes (LED) with Sn content of 8 at. %
Summary
Group-IV light sources based on direct bandgap GeSn and indirect bandgap SiGeSn alloys, which can be monolithically integrated on silicon, receive rising attention currently. The charge carriers in those structures are spatially confined to the optically active region, leading to enhanced radiative recombination rates Along these lines, the lasing threshold current density could be reduced by several orders of magnitude compared to homojunction structures, due to the dimensionality induced changes of the density of states. They offer advantages for light detectors [11,12] or optical modulators based on the quantum confined Stark effect, where strong spectral shift of the absorption edge with an applied electric field can be induced [13,14] Such heterostructures can improve tunneling effects, like negative differential resistance in tunneling diodes, recently demonstrated in [15] for p-i-n Ge0.89Sn0.11 homojunctions. We demonstrate that MQW heterostructures with direct bandgap GeSn wells, type I alignment for both L and Γ- valleys and reasonable barrier-well offsets can be obtained in {SiGeSn/GeSn} MQWs
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