Conductivity-Type Conversion in Self-Assembled GeSn Stripes on Ge/Si(100) under Electric Field

We report on the electronic properties of self-assembled Ge99Sn1 stripes surrounded by inhomogeneous Ge96.6Sn3.4 area resulting from the segregation and migration of Sn droplets on Ge89.5Sn10.5/Ge/Si(100). The sample with microscale patterns was characterized at the nanoscale by a combination of techniques including X-ray diffraction, Raman spectroscopy, and scanning probe microscopy. Kelvin probe force microscopy (KPFM) nanoscale maps of the local work function show a spatial inhomogeneity up to 200 meV, which is explained by the band bending induced by holes trapped at the surface states of the Sn droplets. The scanning capacitance microscopy (SCM) of the local charge carrier density shows the dominant p-type conductivity with lateral variation in the hole-density by 1 order of magnitude. The microscale patterns are depleted by holes, and we experimentally revealed an electric-field-induced conductivity-type conversion from p to n in a self-assembled GeSn stripe. Finally, we presented a model and calculations that support the described above experimentally observed phenomena. This work explicitly provides an understanding of the electronic properties of the GeSn micrometer-scale stripes that is important for the implementation of the GeSn in photonic, optoelectronic, electronic, and energy storage devices.