Simulation of hole transport in p-channel Si MOSFETs

Electron transport in Si inversion layers has been the primary subject of research for many years now [1], but hole transport has been relegated to the background mainly due to the highly complicated valence band-structure in Si. Hole transport is affected by the warping and anisotropy of the valence bands and the band-structure cannot be approximated with an effective mass picture or with an analytical band model. The advent of alternate device structures [2,3&4] aimed at boosting the speed and density of VLSI circuits however, seems to have revived interest. In this paper, we describe an effective way of incorporating band-structure and quantum effects on hole transport in conventional Si p-channel MOSFETs. This is achieved by coupling a 2D Poisson-1D discretized 6×6 k.p Hamiltonian solver [5] self-consistently to the Monte Carlo particle-based transport kernel. The 2D Poisson solver sets up the electrostatics of the problem while the discretized 6×6 k.p Hamiltonian solver handles the valence band-structure and includes the effect of the confining potential under the gate, thus providing the subband structure in the channel region. Carriers in the source and drain regions are treated as quasi-3D particles and the band-structure information is included by solving for the eigenenergies the regular 6×6 k.p Hamiltonian. The subband structure and the carrier scattering rates thus have to be updated frequently during the course of the simulation to make the calculations self-consistent. It is seen that surface roughness and coulomb scattering play a dominant role in limiting the drive current of the device. This method will be applied to study hole transport in strained layer MOSFETs.