Drift mobilities and Hall scattering factors of holes in ultrathin Si1-xGex layers (0.3 < x < 0.4) grown on Si

Sheet resistivity and Hall measurements have been performed on a series of p-type modulation-doped Si/Si1-xGex heterostructures. The structures were g rown by a production-compatible atmospheric-pressure chemical-vapor deposit ion technique and all the epitaxial layers were lattice matched to the sili con substrates. A depleted-doping technique was used to supply the quantum well with holes, and this approach has enabled the transport properties of the SiGe layers to be characterized between 4.2 and 295 K. Measurements of the Hall scattering factor and drift mobility are reported for ultrathin, h igh-Ge content layers (0.3 < x < 0.4) with a range of hole densities up to 4x10(12) cm(-2). The drift mobilities are shown to be substantially and con sistently higher than comparable mobilities reported for holes in Si/SiO2 i nversion layers. A drift mobility of 460 +/- 20 cm(2)/V s was measured at 2 95 K for a 6 nm-thick Si0.65Ge0.35 layer. This is more than a factor of 2 g reater than the equivalent Si inversion layer mobility and is comparable to the highest room-temperature mobilities reported for holes in fully strain ed Si/SiGe heterostructures. The Hall scattering factor is shown to be very dependent upon temperature and, at 295 K, very dependent upon the hole den sity. At 295 K the Hall scattering factor does not exhibit a strong depende nce upon Ge content. The variation of the hole drift mobility with temperat ure has been shown to fit a power dependence mu similar to T-gamma in the r ange 120-300 K. The gamma values are consistent with simple acoustic phonon scattering theory, although a variation in gamma with hole density is also observed, suggesting that a more rigorous theoretical treatment is require d. (C) 2000 American Institute of Physics. [S0021-8979(00)01216-0].