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We have found that GeO 2 /Ge MOS structures fabricated by direct thermal oxidation yield significantly low interface trap density (D it ). Thus, Ge pMOSFETs using the GeO 2 /Ge MOS structures with the superior interface properties have been fabricated for achieving high hole mobility and investigated for examining the impact of the interface properties on the device performance. Al 2 O 3 or SiO films were employed for protecting the GeO 2 /Ge MOS structures during the FET fabrication processes. The relationship between mobility and the fabrication conditions, such as the oxidation temperature, the annealing gas species, the substrate impurity concentration, the thickness of Al 2 O 3 cap, and the surface orientation have been clarified.

The exact analytical forms of the low-temperature thermodynamic quantities and correlation functions are obtained for classical one-dimensional Heisenberg ferromagnets with single-site anisotropy including both the systems with an easy axis and with an easy plane. The problem has been managed on the basis of the functional integral method. The calculated results have a few leading terms in series-expansion with respect to the reduced temperature, exhibiting the characteristic points borne out in the recent numerical studies. In particular, the longitudinal correlation function and susceptibility of the system with an easy axis show Ising-like behaviours and the transverse counterparts of the system with an easy plane show isotropic XY- or Heisenberg-like behaviours. Physical implications of the calculated results are also discussed.