Theoretical Calculation Of Electrical Properties Of Ge FinFET

With the increasing development of microelectronics technology,the size of the device is getting closer to its physical limit,so that the short channel effects is not negligible.As a multi-gate device,FinFET can suppress the short channel effects well,and it is compatible with the existing process.The electron and hole mobility of germanium is about 2.5 times and 4.4 times that of silicon,respectively.Besides,germanium and silicon are in the IV group,with germanium as the channel material,which can increase the drive current and integration.In this paper,we carried out a thorough theoretical analysis on the effects of phonon scattering and channel-gate dielectric interface scattering on the electrical performance of Ge nFinFET.Based on the effective mass approximation theory,we studied the effect of phonon scattering on the mobility of devices under different wafer orientation and channel direction.The coupled Schr?dinger-Poisson equations are solved self-consistently to calculate the electronic structures for the two-dimensional electron gas,and Fermi's Golden Rule is used to calculate the phonon scattering rate,then the corresponding mobility is obtained.It is concluded that the intra-valley acoustic phonon scattering is the dominant mechanism limiting the electron mobility in Ge nFinFETs;Fin directions of[110]?[1~—10]?[1~—1~—0]?[11~—0]within(001)-oriented wafers,[11~—2]?[11~—2~—]?[1~—12~—]?[1~—12]within(110)-oriented wafers,and[1~—10]?[1~—01]?[01~—1]?[11~—0]?[101~—]?[011~—]within(111)-oriented wafers provide the maximum values of electron mobility.The optimized fin width for mobility is also dependent on wafer orientation,channel direction and inversion charge density.Based on the study of the channel-gate dielectric interface,it is concluded that the interface fluctuation could reduce the device mobility by about 50%.The positive and negative of the interface fixed charge will not affect the relationship between the mobility and the inversion charge density,but the lareger the charge,the smaller the mobility.The fixed charge of the interface does not affect the subthreshold swing of the device,but only affects its threshold voltage.The larger the positive charge,the more negative the threshold voltage is.The donor-type interface trap below the intrinsic energy has the small effect on the device characteristic.Because only the donor-type interface trap near the intrinsic energy can capture electrons to change from positive charge to neutral with applying the gate voltage.The acceptor-type interface trap above intrinsic energy has a great influence on the device.The greater the interface state density,the closer to the intrinsic energy,the larger the impact on the device.This is because that with applying the gate voltage,the acceptor-type interface trap near the intrinsic energy is occupied by electrons firstly and more probably.