Abstract
Two series of Ge0.8Sn0.2 samples were grown on Ge buffered Si substrate by molecular beam epitaxy (MBE) to investigate the influence of growth temperature and film thickness towards the evolution of surface morphology. A novel phenomena was observed that the Ge0.8Sn0.2 film was segregated and relaxed by the formation of GeSn stripes on the film. Under specific growth condition, the stripes can cover nearly the whole surface. XRD, TEM, AFM, PL and TEM results indicated that the stripes are high quality single crystalline GeSn with Sn content around 5%. The formation of GeSn stripes proposes an effective strategy to fabricate high crystalline quality GeSn stripe on Si, where the Ge0.8Sn0.2 film serves as precursor and the segregated Sn works as catalyst droplets. This technique has great potential for future optoelectronic and microelectronic applications.
Highlights
The application of GeSn material faces great challenges in the growth of GeSn film on Si and Ge substrate
If the driving energy of segregated Sn is too small to drive the Sn droplets moving on the surface, the segregated Sn tends to leave motionless Sn particles on the film, while the drive force is bigger enough to drive Sn droplets moving on the surface, the moving Sn droplets would etching the GeSn material it passed by or leave Sn wires behind
Combining the results extract from Series A,B samples and previous work, it can be found that the formation of GeSn stripes is originate from the segregated Sn caused by excessive epitaxial temperature and the relaxation of GeSn film, just as the Sn segregation phenomenon observed in previous work
Summary
Temperature and the occupation area of GeSn stripes. Under certain growth temperature, the stripes covers nearly the whole surface of the film. XRD, TEM, AFM and PL tests are performed and their results indicate that the stripes on Ge0.8Sn0.2 film are high quality single crystalline GeSn with 5% Sn content, and the stripes are formed by the migration of segregated Sn on Ge0.8Sn0.2 film driven by the Gibbs energy gap between the Ge0.8Sn0.2 film and GeSn stripes. These above results indicate that for high Sn content GeSn films, the over critical thickness growth may cause the segregation of Sn on the surface. This is a phenomena can help us understand how Sn and Ge atom interact during epitaxy, and can be used for producing GeSn stripes with high crystalline quality, which has extensive application in Si-based nanoelectronics and optoelectronics
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