Microstructure of epitaxial (InGa)As on a borosilicate glass-bonded compliant substrate

A wafer bonding approach to fabrication of a universal compliant substrate for epitaxial growth of high-quality nitride and other materials is described. The compliant substrate consists of an approximately 10 nm thick GaAs template layer that is wafer-bonded to a 0.5 μm thick layer of borosilicate glass that was deposited on a GaAs handle wafer. To test the approach, ∼2 μm thick films of (In_0.45Ga_0.55)As (3.1% mismatch with GaAs) were deposited on the substrates. Orientation Imaging Microscopy of a sample cross-section showed that the (In_0.45Ga_0.55)As layer had the same crystallographic orientation throughout the 2 mm long section examined. These results demonstrate that the template layer is successfully transferred to the glass-coated handle wafer by wafer bonding and that epitaxial growth on the template is achieved. Diffraction contrast transmission electron microscopy (TEM) revealed a mismatch dislocation network at the (InGa)As/GaAs interface. The local dislocation spacing varied from place to place and was considerably larger (on the order of ∼50-100 nm) than the computed value of about 8 nm. These results suggest that mechanisms of strain relaxation other than mismatch dislocation formation may occur in the compliant substrate.