Hole density and strain dependencies of hole effective mass in compressively strained Ge channel structures

The hole density and strain dependencies of the hold effective mass (m*) in the compressively strained Ge channel structures were studied. The hole density was largely modified by front gate bias and it was found that m* drastically increased with the increase of hole density. This is due to the strong nonparabolicity of the heavy-hole band. The strain dependence of m* was also investigated based on a series of Ge channel samples grown on SiGe buffer layers with various Ge concentrations. It was revealed that m* decreases with the increase of strain, indicating that Ge channels with larger strain are more advantageous for high-performance device applications.