Spontaneously Conversion from Film to High Crystalline Quality Stripe during Molecular Beam Epitaxy for High Sn Content GeSn

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.

Insights into the Origins of Guided Microtrenches and Microholes/rings from Sn Segregation in Germanium–Tin Epilayers

“…This also explains the occurrence of more Sn segregation with white spots when the growth temperature decreases from 300 14 to 280°C (Part 3.1), which can be attributed to the Sn content that exceeds the threshold value of 8% (bigger Gibbs free energy gap). We notice that our obtained results are slightly different from the recent MBE growth experiment from Wang et al 17 where the density of white-spots increases when the growth temperature increases from 155 to 175 °C. This result is due to the constant of Sn-content of the GeSn films at 20% during growth while the increase of the substrate temperature increases the migration of Sn atoms.…”

“…From the thermodynamic point of view, the migration of the droplets requires large Gibbs free-energy change between the supersaturated GeSn film and crystalline stable Ge (or low-content GeSn). The Gibbs free-energy change for Sn segregation can be written as , where Δ G V is the reduction of the free energy from the high supersaturation GeSn to Ge (or low-content GeSn) and Sn droplet, which is determined by the mixing enthalpy and entropy. Δ G S is the changes of strain energy from compressive GeSn films to strain-free Ge (or low-content GeSn).…”

“…From the thermodynamic point of view, the migration of the droplets requires large Gibbs free energy change between the supersaturated GeSn film and crystalline stable Ge (or low-content GeSn). The Gibbs free energy change for Sn segregation can be written as 17,26…”

“…Several studies have reported two main morphological evolutions for the phase separation process: the development of the densely-packed, isolated Sn-rich islands (droplets) [11][12][13] , and the self-assembly of surface trenches caused by the movement of Sn droplets on surfaces. [14][15][16][17] Despite the report of numerous studies in exploring the relationship between the Sn segregation and the heating temperature, strain relaxation and dislocation formation, [9][10][11][12][13][14] the fundamental mechanisms of the two abovementioned morphological evolutions remain inconclusive. Among the GeSn research communities, much effort has been focused on the growth of high quality GeSn.…”

“…The phase separation in the GeSn films caused by low thermal solubility has been observed not only during growth but also during thermal treatments. Several studies have reported two main morphological evolutions for the phase separation process: the development of the densely packed, isolated Sn-rich islands (droplets) − and the self-assembly of surface trenches caused by the movement of Sn droplets on surfaces. − Despite the report of numerous studies in exploring the relationship between the Sn segregation and the heating temperature, strain relaxation, and dislocation formation, − the fundamental mechanisms of the two abovementioned morphological evolutions remain inconclusive. Among the GeSn research communities, much effort has been focused on the growth of high-quality GeSn. , Meanwhile, there have been limited studies on the growth of GeSn layers with Sn segregation, where a systematic explanation on the mechanism is called for.…”