Growth, structural, and electrical properties of germanium-on-silicon heterostructure by molecular beam epitaxy

• Published in: AIP advances 2017-09, Vol.7 (9), p.095214-095214-15
• Main Authors: Ghosh, Aheli, Clavel, Michael B., Nguyen, Peter D., Meeker, Michael A., Khodaparast, Giti A., Bodnar, Robert J., Hudait, Mantu K.
• Format: Article
• Language: English
• Subjects: Carrier mobility; Dislocation density; Electrical measurement; Electrical properties; Electron mobility; Electronic devices; Energy distribution; Epitaxial growth; Germanium; Hall effect; Heterostructures; Molecular beam epitaxy; Morphology; MOS devices; Photomicrographs; Resistance; Silicon; Strain analysis; Surface roughness; Temperature dependence; Thermal expansion; Thin films; Transmission electron microscopy; X-ray diffraction
• ISSN: 2158-3226; 2158-3226
• DOI: 10.1063/1.4993446

The growth, morphological, and electrical properties of thin-film Ge grown by molecular beam epitaxy on Si using a two-step growth process were investigated. High-resolution x-ray diffraction analysis demonstrated ∼0.10% tensile-strained Ge epilayer, owing to the thermal expansion coefficient mismatch between Ge and Si, and negligible epilayer lattice tilt. Micro-Raman spectroscopic analysis corroborated the strain-state of the Ge thin-film. Cross-sectional transmission electron microscopy revealed the formation of 90    ° Lomer dislocation network at Ge/Si heterointerface, suggesting the rapid and complete relaxation of Ge epilayer during growth. Atomic force micrographs exhibited smooth surface morphology with surface roughness < 2 nm. Temperature dependent Hall mobility measurements and the modelling thereof indicated that ionized impurity scattering limited carrier mobility in Ge layer. Capacitance- and conductance-voltage measurements were performed to determine the effect of epilayer dislocation density on interfacial defect states (D it ) and their energy distribution. Finally, extracted D it values were benchmarked against published D it data for Ge MOS devices, as a function of threading dislocation density within the Ge layer. The results obtained were comparable with Ge MOS devices integrated on Si via alternative buffer schemes. This comprehensive study of directly-grown epitaxial Ge-on-Si provides a pathway for the development of Ge-based electronic devices on Si.