Role of Si1-xGex buffer layer on mobility enhancement in a strained-Si n-channel metal-oxide-semiconductor field-effect transistor

Strained-Si n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated on molecular-beam epitaxially grown strained Si with various Si1-xGex buffer layers. Effective electron mobility in n-MOSFETs with a Si1-xGex (x = 0.2, 0.3) graded buffer layer was 60% higher than that in an unstrained-Si n-MOSFET. However, mobility of samples with a Si1-xGex buffer layer on a low-temperature grown Si buffer layer was not increased as much as that of samples on a graded buffer layer. Atomic-force microscopic observation suggests that the power spectrum of surface roughness of the strained-Si layer varies according to the buffer layer, and this variation may affect the enhancement of mobility. (C) 1999 American Institute of Physics. [S0003-6951(99)01545-4].