Research On Electron Mobility Of Main-Valley And Sub-valley In Strained Si

Although providing a continual performance improvement of integrated circuits, geometric scaling of Si devices can not enhance carrier mobility physically. A key method to improve device performance is to enhance the carrier transport by changing the material properties. A promising candidate is strained Si which has the advantage of high-mobility and adjustable energy structure. In the current semiconductor industry, Si-based strained devices and circuits have been in practical use.This work dealt with electron mobility of main-valley and sub-valley in strained Si. Firstly, with principle of stress introduction demonstrated, research on the effect of stress of different type on band structure of Si has been done and the parameters: density-of-state effective mass and conductivity effective mass, necessary to solve mobility, were obtained. Secondly, based on the quantum mechanical theory, three electron scattering mechanisms in conduction band, including ionized impurity scattering, acoustical phonon scattering and inter-valley phonon scattering, have been specifically analyzed, and the corresponding model of electron scattering set up. With average relaxation time and scattering probability calculated, at 300K, electron mobilities of main-valley and sub-valley in strained Si were deduced. The mechanism of enhancement in mobility of strained Si was also given. Since mobility in sub-valley was lower than that in main-valley, with reference of RWH (Ridley-Watkins-Hilsum) standard, the conclusion that there existed a weak transferred electron effect in strained Si was drawn.At room temperature, electron mobility of main-valley in strained Si has reached as high as 3012.86 cm2/V.s for Ge fraction of 0.3, an obvious enhancement compared with conventional Si. Moreover, mobility of sub-valley in strained Si was calculated for the first time.