Hole effective masses of p-type metal-oxide-semiconductor inversion layer in strained Si_(1-x)Ge_x alloys channel on (110) and (111) Si substrates

摘要

Valence subband properties and hole effective masses of PMOS inversion layer in strained Si_(1-x)Ge_x, alloys channel on (110) and (111) Si substrates are studied theoretically based on the Luttinger-Kohn Hamiltonian. The subband structures under investigation are a result of the quantized levels produced by the triangular quantum well in the inversion layer created by the applied gate bias in the z-direction. Valence subband properties including constant-energy-contours, density-of-states, quantized effective mass in the z-direction m_z, carrier concentration effective mass m_(cc), and conductivity effective mass m_σ are calculated as functions of the Ge concentration at gate electric field of 1 MV/cm. An analytic expression for the Fermi level is derived in terms of m_(cc), the total hole concentration, and subband edges. Our results show that in general m_σ in the (110) system is lower than that in the (111) substrate orientation, which implies that (110) Si substrate is more favorable for carrier transport. Furthermore, m_σ in the [-110] direction of the (110) Si substrate system are the lightest among all other cases.