Influence of doping on the nanomechanical behavior of InGaP/Ge thin films

[Indium gallium phosphide, InGaP thin films with and without Si doping was deposited on Ge substrate by metal-organic vapor phase epitaxy. A lattice mismatch between InGaP alloy and Ge substrate of -5.0×10-3, corresponding to an average In content of x(In)=42.7% is obtained by high resolution X-ray diffraction. Reciprocal lattice maps showed peak broadening that can be attributed to both compositional variation of the alloy and to the presence of defects associated with strain release. The deformation mechanisms of these thin films were studied using nanoindentation with Berkovich diamond indenter. Our experiments provide consistent evaluations of reduced modulus and hardness. The material pile-up and sink-in regions around the indentation impression for the ternary In1-xGaxP/Ge epilayers were observed. The unloading curves are not completely featureless but a change in slope or a very weak kinking observed owing to the minor deviation from ideal elastic-plastic behavior. The understanding and exploitation of this phenomenon might be useful for improving the microscopic surface properties of InxGa1-xP/Ge epilayers. This study reports that the mechanical properties of the films grown at constant growth temperature strongly depend on the doping effect.