EVIDENCE FOR A METAL-INSULATOR-TRANSITION AT B=0 IN SI SIGE/SI QUANTUM-WELLS/

The temperature dependence of the resistivity of gated Si-SiGe quantum -well structures has revealed a metal-insulator transition as a functi on of carrier density at zero magnetic field. Although early scaling t heories have argued against the existence of a metal-insulator transit ion at zero temperature in infinite two-dimensional systems, it is now clear experimentally that such a transition can occur in systems with short-range scatterers. We have studied the magneto-transport propert ies of holes confined in strained p-type Si-Si0.87Ge0.13-Si quantum we lls grown by ultra-high-vacuum chemical-vapor deposition. In the tempe rature range 25 mK-4.2 K, there is a transition from an insulating pha se at low carrier densities to a metallic phase at high carrier densit ies with a transition boundary near 3.3 x 10(11) cm(-2) Evidence for a Coulomb gap is presented in the insulating phase.