Carrier mobilities in modulation doped Si1-xGex heterostructures with respect to FET applications

Room temperature carrier mobilities in both p- and n-type modulation doped SiGe heterostructures were investigated by the magnetic field dependent Hal l (B-Hall) technique. B-Hall allows a selective determination of mobility a nd sheet carrier density in the channel and in parasitic parallel conductin g layers. The heterostructures grown by MBE on Si (100) substrates consiste d of a strained Si1-xGex, channel on a Si1-yGey strain relieved buffer (SRB ) with x - y = 0.3. Structural assessment was done by high resolution X-ray diffraction (HR-XRD) and cross-sectional TEM (XTEM). The hole mobility in p-type heterostructures depends clearly on the Ge content x in the channel and increases from 635 cm(2)/Vs for a SiGe alloy layer with x = 0.67 up to 1665 cm(2)/Vs for a pure Ge channel, which is close to the value of undoped bulk Ge. For the corresponding n-type structure with a Si channel on a Si0 .7Ge0.3 SRB, a room temperature electron mobility of 2700 cm(2)/Vs was meas ured. (C) 1998 Elsevier Science S.A. All rights reserved.