Low-frequency noise in Si1-xGex p-Channel metal oxide semiconductor field-effect transistors

Low-frequency noise (LFN) in Si1-x Gex p-channel Metal Oxide Semiconductor Field-Effect Transistors (pMOSFETs) with a relatively wide range of Ge fraction x = 0.2, 0.5, 0.7, and Si1-xGex thickness dSiGe of 2-14 nm are investigated. Although LFN of Si1-x Gex pMOSFETs seems to be complicated functions of dSiGe and Ge fraction, it is shown that LFN in Si1-x Gex pMOSFETs can be lower than that in conventional Si pMOSFETs. Moreover, in order to evaluate the trap density at the Si1-xGex/Si heterostructure interface, the noise power at bias conditions showing the maximum transconductance gmMAX is examined. At the bias conditions, drain current is confirmed to flow mainly in the buried Si1-x Gex channel, but not in the surface Si channel. Surface generation current is also examined to evaluate the trap density at the interface between the gate oxide and the Si capping layer. The dependence of the noise power on dSiGe and Ge fraction corresponds well to that of gmMAX, but not to that of the surface generation current. It is concluded that the noise characteristics at the gmMAX bias conditions reflect the trap density at the Si1-xGex/Si heterostructure interface, and correspond well to gmMAX behaviour.