Raheel Shah | Sultan Qaboos University (original) (raw)

Papers by Raheel Shah

Proceedings of the World Congress on …, Jan 1, 2009

Bulk phonon limited mobility in silicon based MOSFETs, have long been observed to demonstrate a -... more Bulk phonon limited mobility in silicon based MOSFETs, have long been observed to demonstrate a -1/3rd dependence on the effective transverse field at room and higher temperatures. However, despite significant effort, existing phonon scattering models fail to reproduce this dependence. This paper reports on the impact of approximations used in the calculation of the intra-valley scattering rate in existing models which causes a much reduced dependence of phonon limited mobility on the effective field. An expression for scattering rate in the absence of such approximations is derived. The improvement of the new complex model is however, insufficient to match experiment. To improve the situation an empirical model is proposed with deformation potentials dependent on the inversion sheet concentration.

Proceedings of the World Congress on …, Jan 1, 2009

The comprehensive Ando' surface roughness (SR) model is implemented for nMOSFETs. Four distinct s... more The comprehensive Ando' surface roughness (SR) model is implemented for nMOSFETs. Four distinct source terms contribute in SR scattering. Relative strength of these contributing source terms are evaluated and compared. The most influential term turned out to be due to scattering with the "physical steps" at the interface. Remote SR scattering is also significant in ultra-thin MOS structures. The proposed model of Gámiz et al for remote SR scattering is studied. It is shown that modification to the Gámiz model is necessary in order to observe the full impact of rms height of the abrupt "steps".

Lecture Notes in Engineering and Computer …, Jan 1, 2011

Impact of induced strain on charge carrier mobility is investigated for a monolayer graphene shee... more Impact of induced strain on charge carrier mobility is investigated for a monolayer graphene sheet. Mobility is computed within Born approximation by including impurity scattering, surface roughness effects and interaction with lattice phonons. Unlike its sSi counterpart, strained graphene shows a drop in mobility with increasing strain. Main reason for this effect is decrease in Fermi velocity due to induced distortions in the graphene honeycomb. Effect of temperature on graphene mobility under varying strain is studied. Non symmetric temperature dependence was observed for the two crystallographic orientations.

Thin Solid Films, Jan 1, 2008

Germanium is an attractive candidate for ultra fast CMOS technology due to its potential for doub... more Germanium is an attractive candidate for ultra fast CMOS technology due to its potential for doubling electron mobility and quadrupling hole mobility in comparison to silicon. To maintain the requirements of the International Technology Roadmap for Semiconductors (ITRS), high-κ insulators and metal gates will be required in conjunction with Ge technology. Key issues which will have to be addressed in achieving Ge technology are: trap free insulators, assessment of appropriate crystallographic orientations and the selection of gate metals for the best mobility. In this work mobilities are evaluated for Ge-nMOSFET with two metal gates (Al and TiN) and high-κ (HfO 2 ) insulator. Scattering with bulk phonons, surface roughness and high-κ phonons are taken into account. It is predicted that Al as the gate material on Ge {100} substrate performs 50% better than Ge {111} orientation at a sheet concentration of 1 × 10 13 cm − 2 . Surface roughness is likely to be the most damaging mobility degradation mechanism at high fields for Ge {111}.

Electronic Engineering and Computing Technology, Jan 1, 2010

The comprehensive Ando's surface roughness (SR) model examined for nMOSFETs. Four distinct so... more The comprehensive Ando's surface roughness (SR) model examined for nMOSFETs. Four distinct source terms contribute in SR scattering. Relative strength of these contributing source terms are evaluated and compared. The most influential term turned out to be due ...

ABSTRACT Surface optical phonons scattering is essential in determning the channel mobility of hi... more ABSTRACT Surface optical phonons scattering is essential in determning the channel mobility of high-k gate dielectric MOSFETs. Metal gates are believed to modulate the effects of high-k phonons to some extent in comparison to poly-Si gates. In this work nonideal metal gate model is used to study the impact of SO scattering on the nMOSFET channel mobility. Landau damping effects, which are found to be important in the coupled plasmon-phonon scattering, are studied from the perspective of different criteria in selecting the Landau limits.

Arxiv preprint arXiv:1008.4425, Jan 1, 2010

Impact of induced strain on charge carrier mobility is investigated for a monolayer graphene shee... more Impact of induced strain on charge carrier mobility is investigated for a monolayer graphene sheet. Mobility is computed within Born approximation by including impurity scattering, surface roughness effects and interaction with lattice phonons. Unlike its sSi counterpart, strained graphene shows a drop in mobility with increasing strain. Main reason for this effect is decrease in Fermi velocity due to induced distortions in the graphene honeycomb.

Electron Devices, IEEE Transactions …, Jan 1, 2007

The effects of surface phonon scattering in an nMOSFET with a high-κ gate insulator and a nonidea... more The effects of surface phonon scattering in an nMOSFET with a high-κ gate insulator and a nonideal metal gate are examined. The nonideal metal gate model depends on three parameters: 1) the density of electrons in the gate; 2) the electron effective mass; and 3) the high-frequency dielectric constant associated with the choice of gate metal. The impact of these parameters on surface optical (SO) mobility is demonstrated using TiN as an example. For the selected choice of parameters and Landau damping limits, the results indicate that SO phonon scattering does not seem to play a significant role in the mobility degradation of TiN/HfO 2 MOSFETs for the entire range of sheet concentration.

Proceedings of the World Congress on …, Jan 1, 2009

Bulk phonon limited mobility in silicon based MOSFETs, have long been observed to demonstrate a -... more Bulk phonon limited mobility in silicon based MOSFETs, have long been observed to demonstrate a -1/3rd dependence on the effective transverse field at room and higher temperatures. However, despite significant effort, existing phonon scattering models fail to reproduce this dependence. This paper reports on the impact of approximations used in the calculation of the intra-valley scattering rate in existing models which causes a much reduced dependence of phonon limited mobility on the effective field. An expression for scattering rate in the absence of such approximations is derived. The improvement of the new complex model is however, insufficient to match experiment. To improve the situation an empirical model is proposed with deformation potentials dependent on the inversion sheet concentration.

Proceedings of the World Congress on …, Jan 1, 2009

The comprehensive Ando' surface roughness (SR) model is implemented for nMOSFETs. Four distinct s... more The comprehensive Ando' surface roughness (SR) model is implemented for nMOSFETs. Four distinct source terms contribute in SR scattering. Relative strength of these contributing source terms are evaluated and compared. The most influential term turned out to be due to scattering with the "physical steps" at the interface. Remote SR scattering is also significant in ultra-thin MOS structures. The proposed model of Gámiz et al for remote SR scattering is studied. It is shown that modification to the Gámiz model is necessary in order to observe the full impact of rms height of the abrupt "steps".

Lecture Notes in Engineering and Computer …, Jan 1, 2011

Impact of induced strain on charge carrier mobility is investigated for a monolayer graphene shee... more Impact of induced strain on charge carrier mobility is investigated for a monolayer graphene sheet. Mobility is computed within Born approximation by including impurity scattering, surface roughness effects and interaction with lattice phonons. Unlike its sSi counterpart, strained graphene shows a drop in mobility with increasing strain. Main reason for this effect is decrease in Fermi velocity due to induced distortions in the graphene honeycomb. Effect of temperature on graphene mobility under varying strain is studied. Non symmetric temperature dependence was observed for the two crystallographic orientations.

Thin Solid Films, Jan 1, 2008

Germanium is an attractive candidate for ultra fast CMOS technology due to its potential for doub... more Germanium is an attractive candidate for ultra fast CMOS technology due to its potential for doubling electron mobility and quadrupling hole mobility in comparison to silicon. To maintain the requirements of the International Technology Roadmap for Semiconductors (ITRS), high-κ insulators and metal gates will be required in conjunction with Ge technology. Key issues which will have to be addressed in achieving Ge technology are: trap free insulators, assessment of appropriate crystallographic orientations and the selection of gate metals for the best mobility. In this work mobilities are evaluated for Ge-nMOSFET with two metal gates (Al and TiN) and high-κ (HfO 2 ) insulator. Scattering with bulk phonons, surface roughness and high-κ phonons are taken into account. It is predicted that Al as the gate material on Ge {100} substrate performs 50% better than Ge {111} orientation at a sheet concentration of 1 × 10 13 cm − 2 . Surface roughness is likely to be the most damaging mobility degradation mechanism at high fields for Ge {111}.

Electronic Engineering and Computing Technology, Jan 1, 2010

The comprehensive Ando's surface roughness (SR) model examined for nMOSFETs. Four distinct so... more The comprehensive Ando's surface roughness (SR) model examined for nMOSFETs. Four distinct source terms contribute in SR scattering. Relative strength of these contributing source terms are evaluated and compared. The most influential term turned out to be due ...

ABSTRACT Surface optical phonons scattering is essential in determning the channel mobility of hi... more ABSTRACT Surface optical phonons scattering is essential in determning the channel mobility of high-k gate dielectric MOSFETs. Metal gates are believed to modulate the effects of high-k phonons to some extent in comparison to poly-Si gates. In this work nonideal metal gate model is used to study the impact of SO scattering on the nMOSFET channel mobility. Landau damping effects, which are found to be important in the coupled plasmon-phonon scattering, are studied from the perspective of different criteria in selecting the Landau limits.

Arxiv preprint arXiv:1008.4425, Jan 1, 2010

Impact of induced strain on charge carrier mobility is investigated for a monolayer graphene shee... more Impact of induced strain on charge carrier mobility is investigated for a monolayer graphene sheet. Mobility is computed within Born approximation by including impurity scattering, surface roughness effects and interaction with lattice phonons. Unlike its sSi counterpart, strained graphene shows a drop in mobility with increasing strain. Main reason for this effect is decrease in Fermi velocity due to induced distortions in the graphene honeycomb.

Electron Devices, IEEE Transactions …, Jan 1, 2007

The effects of surface phonon scattering in an nMOSFET with a high-κ gate insulator and a nonidea... more The effects of surface phonon scattering in an nMOSFET with a high-κ gate insulator and a nonideal metal gate are examined. The nonideal metal gate model depends on three parameters: 1) the density of electrons in the gate; 2) the electron effective mass; and 3) the high-frequency dielectric constant associated with the choice of gate metal. The impact of these parameters on surface optical (SO) mobility is demonstrated using TiN as an example. For the selected choice of parameters and Landau damping limits, the results indicate that SO phonon scattering does not seem to play a significant role in the mobility degradation of TiN/HfO 2 MOSFETs for the entire range of sheet concentration.