Growth of highly tensile-strained Ge on relaxed InxGa1-xAs by metalorganic chemical vapor deposition

Highly tensile-strained Ge thin films and quantum dots have the potential to be implemented for high mobility metal-oxide-semiconductor field-effect transistor channels and long-wavelength optoelectronic devices. To obtain large tensile strain, Ge has to be epitaxially grown on a material with a larger lattice constant. We report on the growth of tensile-strained Ge on relaxed InxGa1-xAs epitaxial templates by metal-organic chemical vapor deposition. To investigate the methods to achieve high quality Ge epitaxy on III-V semiconductor surfaces, we studied Ge growth on GaAs with variable surface stoichiometry by employing different surface preparation processes. Surfaces with high Ga-to-As ratio are found to be necessary to initiate defect-free Ge epitaxy on GaAs. With proper surface preparation, tensile-strained Ge was grown on relaxed InxGa1-xAs with a range of In content. Low growth temperatures between 350 and 500 degrees C suppress misfit dislocation formation and strain relaxation. Planar Ge thin films with tensile strain as high as 0.5% were fabricated on relaxed In0.11Ga0.89As. For relatively high In-content (x > 0.2) InxGa1-xAs templates, we observed an islanded growth morphology forming tensile-strained Ge quantum dots. Tensile strain as high as 1.37% was measured in these Ge quantum dots grown on In0.21Ga0.79As. The ability to grow these structures will enable us to further study the electronic and optoelectronic properties of tensile-strained Ge. (c) 2008 American Institute of Physics. [DOI: 10.1063/1.3005886]