Growth of highly tensile-strained Ge on relaxed InxGa1−xAs by metal-organic 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 ${\text{In}}_x{\text{Ga}}_{1-x}\text{As}$ 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 ${\text{In}}_x{\text{Ga}}_{1-x}\text{As}$ with a range of In content. Low growth temperatures between 350 and $500°\text{C}$ suppress misfit dislocation formation and strain relaxation. Planar Ge thin films with tensile strain as high as 0.5% were fabricated on relaxed ${\text{In}}_{0.11}{\text{Ga}}_{0.89}\text{As}$ . For relatively high In-content $\left(x>0.2\right)$ ${\text{In}}_x{\text{Ga}}_{1-x}\text{As}$ 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 ${\text{In}}_{0.21}{\text{Ga}}_{0.79}\text{As}$ . The ability to grow these structures will enable us to further study the electronic and optoelectronic properties of tensile-strained Ge.