Warpage of GaAs-on-Si wafers and its reduction by selective growth of GaAs through a silicon shadow mask by molecular beam epitaxy.

The warpage of GaAs-on-Si wafers, caused by the different thermal expansion coefficients of GaAs and Si, has been studied as a function of the GaAs thickness on 3 inch diameter Si wafers. The warpage increases from 7microns to 52microns as the GaAs layer thickness increases from 1.2microns to 4.2microns. Under vacuum clamping conditions the GaAs/Si wafers can be forced to the original flatness. By growing GaAs selectively through a Si shadow mask as islands of 1mmx1mm size with a periodicity of 2mm in 5cmX5cm central area of the wafer, the warpage was reduced considerably. Spatially resolved cathodoluminescence (CL) spectra indicated that the tensile strain is reduced significantly within 10microns from the edge of the growth. Near the edge, the CL intensity is also increased indicating a reduction in nonradiative recombination at defects. The use of the Si shadow mask to obtain patterned growth is relatively simple, requiring no processing step before or after the growth, and has a great potential in the integration of GaAs and Si circuits or devices.