Abstract
We report on the direct observation of lattice relaxation and Sn segregation of GeSn/Ge/Si heterostructures under annealing. We investigated strained and partially relaxed epi-layers with Sn content in the 5 at. %-12 at. % range. In relaxed samples, we observe a further strain relaxation followed by a sudden Sn segregation, resulting in the separation of a β-Sn phase. In pseudomorphic samples, a slower segregation process progressively leads to the accumulation of Sn at the surface only. The different behaviors are explained by the role of dislocations in the Sn diffusion process. The positive impact of annealing on optical emission is also discussed.
Highlights
Semiconductor heterostructures comprising GeSn alloys are more and more considered a serious candidate as active material for light emitting devices integrated into the Si-CMOS technology[1] after the demonstration of lasing using this material system.[2,3,4] in order to move toward real-market applications, several issues still have to be addressed such as the low laser operating temperature
Li et al.[6] indicate that GeSn layers pseudormorphically grown on Ge buffers undergo plastic strain relaxation by thermal treatment above 420 ◦C, as evidenced by the formation of a strain relieving misfit dislocation (MD) network at the GeSn/Ge interface and of threading dislocations (TD) in the GeSn layers
The asymmetry of the GeSn(004) peak of partly relaxed samples indicates a variation of the Sn content over the layer depth, since Sn incorporation is slightly elevated after the onset of relaxation, as the larger lattice constant allows for an increased number of Sn atoms to be built into the crystal.[14]
Summary
Semiconductor heterostructures comprising GeSn alloys are more and more considered a serious candidate as active material for light emitting devices integrated into the Si-CMOS technology[1] after the demonstration of lasing using this material system.[2,3,4] in order to move toward real-market applications, several issues still have to be addressed such as the low laser operating temperature. Marconi 446, I-00146 Rome, Italy (Received April 2018; accepted June 2018; published online 30 July 2018)
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