Phosphorus-doped n-type homoepitaxial diamond films have been successfully grown at high substrate temperatures (> 1000 degrees C) on high-pressure/high-temperature-synthesized type-Ib single-crystalline diamond (1 0 0) substrates, by using a conventional microwave plasma chemical-vapor-deposition (CVD) system with high power densities. The deposition system employed in this work had an easily exchangeable 36 mm inner-diameter quartz-tube growth chamber. The homoepitaxial diamond films thus grown were characterized by means of Hall-effect measurements with an AC magnetic field, atomic force microscope observations and secondary ion mass spectrometry techniques. The dependences of the substrate temperature (<= 1300 degrees C) and the P/C ratio in the source gas (<= 9900 ppm) on the specimen features were investigated. The optimum substrate temperature deduced was approximate to 1160 degrees C, which was also applicable to the CVD growth of undoped homoepitaxial diamond layers. The n-type conductions with an activation energy approximate to 0.6 eV were observed for the specimens with amounts of the P atoms incorporated to approximate to 1.5 x 10(18) cm (3) whereas the doping efficiencies changed from approximate to 0.06% to approximate to 0.92% with the growth condition. Possible origins for these results are discussed in relation to the growth mechanism. (C) 2008 Elsevier B.V. All rights reserved.