Influence of Strain on Electrical Properties of the Ge Channel in the Modulation-Doped p-Si 0.5 Ge 0.5 /Ge/Si 1− x Ge x Heterostructure

The influence of strain on the electrical properties of the Ge channel in a modulation-doped p-Si0.5Ge0.5/Ge/Si1-xGex heterostructure is studied in relation to the Si mole fraction (1-x) and the thickness of the Si1-xGex buffer layer. In the range of 1-x≤0.25, the hole concentration and mobility increase with strain in the Ge channel. However, in the range of 1-x>0.25, they decrease with strain due to the large number of threading dislocations. It is also found that hole concentration and mobility increase with buffer layer thickness. As a result, a very high mobility of 7600 cm2V-1s-1 at 77 K is obtained at a Si mole fraction of 0.25 and buffer layer thickness of 1 µm.