Modulation doping in Ge(x)Si(1-x)/Si strained layer heterostructures.

We report the first observation of the modulation doping effect in Si/Ge0.2 Si0.8 heterojunctions grown by molecular beam epitaxy. Peak hole mobilities of ~3,300 cm(2)V(-1)s(-1) have been observed at 4.2K. These values, although non-optimum, are comparable to the best reported values for holes in Si/SiO2 inversion layers. Low temperature, angular dependent, Shubnikov-de Haas measurements have demonstrated the two dimensional nature of the hole gas and yield a surface carrier density of 3.5 x 10 (11) cm(-2).