The nature of the metal-insulator transition in silicon germanide quantum wells.

A study of the temperature dependence of the resistivity of gated SiGe quantum well structures has revealed a metal-insulator transition as a function of carrier density at zero magnetic field. Although early scaling theories (Abrahams et al., 1979) have argued against the existence of a metal-insulator transition at zero temperature in infinite 2D and 1D systems, more recent theoretical results using a random set of two-dimensional point potentials have shown that such a transition is allowed in two dimensions (Az'bel, 1992). Mounting experimental evidence for such a transition in 2D systems with short range scattering has accumulated in both semiconducting and superconducting structures (Kravchenko et al., 1995, and others). Pseudomorphic, CVD-grown p-type Si/Si$\sb{0.87}$Ge$\sb{0.13}$/Si quantum wells of various widths (65-200 A) have been studied. The samples were gated using a Ti-Au Schottky gate to allow for carrier density variation. Measurement of the transport to quantum lifetime ratio indicates that the transport is dominated by short range scattering. In the temperature range from 400 mK - 4.2 K, the temperature dependence shows a transition from a metallic phase in the high density regime to an insulating phase in the low density regime with a transition boundary close to 2.2 $\times$ 10$\sp $ cm$\sp{-2}$. The scaling properties of the observed metal-insulator transition will be discussed, and compared to previous scaling results from silicon MOSFETs. Below 400 mK, the onset of another transition is accompanied by a sharp drop in resistivity with temperature followed by a monotonic decrease in resistivity below 115 mK. The phase diagram was explored using temperature and density dependences of the current-voltage characteristics