Slurry-Free Chemical Mechanical Planarization (CMP) of Engineered Germanium-on-Silicon Wafers

Background: Germanium has been widely considered as an interlayer to facilitate III-V integrations on silicon. For instance demand for low-cost and high-efficiency solar cells has motivated the development and use of germanium-on-silicon (Ge/Si) heterostructures to extend the optoelectronic application of Si technology. Numerous manufacturers as well as research groups are currently exploring engineered Ge/Si structures for direct heteroepitaxy of gallium arsenide (GaAs) for multijunction solar cells. A common challenge for such III-V integration on engineered Ge/Si substrates is to planarize and prepare the Ge surface for subsequent GaAs growth. Touchdown Ge grown on Si using molecular beam epitaxy was subjected to CMP using a dilute hydrogen peroxide solution. The root-mean-square (RMS) roughness of the Ge measured was less than 0.2 nm. As a qualitative indicator of the CMP processs effectiveness subsequently grown GaAs on touchdown Ge/Si substrates has shown room-temperature photoluminescence whose intensity is approaching that from GaAs grown on Ge substrates. Technology Description: This invention is a slurry-free method of Chemical Mechanical Planarization (CMP) of engineered germanium on silicon wafers. Touchdown Ge grown on Si using molecular beam epitaxy was subjected to CMP using a dilute hydrogen peroxide solution. The root-mean-square (RMS) roughness of the Ge measured was less than 0.2 nm. As a qualitative indicator of the CMP process’s effectiveness subsequently grown GaAs on touchdown Ge/Si substrates has shown room-temperature photoluminescence whose intensity is approaching that from GaAs grown on Ge substrates. Applications: Solar cells and optoelectronics