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Valence subband properties and hole effective masses of PMOS inversion layer in strained Si1-xGex 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 mz, carrier concentration effective mass mcc, and conductivity effective mass mσ 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 mcc, the total hole concentration, and subband edges. Our results show that in general mσ 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, mσ in the [-110] direction of the (110) Si substrate system are the lightest among all other cases. [ABSTRACT FROM AUTHOR]

An acoustic mismatch model is used to describe the reflection and transmission of acoustic waves at interfaces of two materials with mismatched impedances. Acoustic attenuation is typically ignored for calculating acoustic impedance, and the parameters in the acoustic mismatch model are thus all real numbers instead of complex numbers. However, acoustic attenuation up to the THz regime is significant. The validity and potential applications of the complex acoustic mismatch model have not been investigated in the sub-THz regime. We report the verification experiments of this model in a complex form. We experimentally measured the amplitude and phase of subpicosecond acoustic pulses, reflected from the interface of GaN and silica. Based on the acoustic mismatch model, the frequency dependence of complex acoustic impedance of silica, which includes the information of sound velocity and attenuation, was experimentally obtained in the sub-THz regime. The acoustic properties of silica were compared with the conventional method, which analyzes the acoustic pulses traveling inside the same silica film. Agreement of sound velocity from two methods was confirmed. The attenuations of the silica film, obtained through using the acoustic mismatch model to analyze the reflected acoustic pulses from silica, were validated by a typical method up to 0.3 THz. This work demonstrates potential applications for characterizing the sub-THz acoustic properties of thick and highly damped materials, which could be challenging by using conventional methods. [ABSTRACT FROM AUTHOR]