The structural and electrical properties of N- and In-polar InN films grown directly on substrates were investigated. The twist contribution of directly grown InN films, which was defined by the estimated X-ray rocking curve's full-width at half-maximum (XRC's FWHM) of InN (1 0 (1) over bar 0) reflection, varied considerably by at least 40 arcmin for both N- and In-polar InN films, depending on growth conditions. In contrast, the tilt contribution, defined by the XRC's FWHM of InN (0 0 0 2) reflection, was roughly fixed at 1.5-2.5 arcmin for N-polar InN films and 8-12 arcmin for In-polar InN films. For samples with the same twist contribution, In-polar InN films had larger tilt contribution than N-polar InN films. Nevertheless, electrical properties of In-polar InN had much better properties than those of N-polar InN films. (C) 2008 Elsevier B.V. All rights reserved.