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Temperature-dependent conductivity and Hall measurements have been carried out on heavily in situ B-doped polycrystalline diamond films in a temperature range from ∼100 to 750 K. The slope of the conductivity is clearly non-Arrhenius leading to a pronounced tail at low temperatures. Carrier transport at low temperatures is dominated by variable range hopping. The activation energy decreases with increasing doping concentration and the most heavily doped diamond films show metallic behavior above room temperature. Hole carrier concentrations up to 1.8×1021 cm−3 were measured in agreement with secondary-ion-mass spectroscopy investigations.

Temperature dependent resistivity and Hall measurements have been carried out on in situ boron doped polycrystalline diamond films. The temperature dependence of the resistivity can be described by a two band conduction model with two conduction mechanisms working parallel. A fair agreement between the depth distribution of the boron concentration determined from spreading resistance and secondary ion mass spectroscopy is found. Room temperature resistivities and activation energies from various sources are compared with the present work. With the aid of these curves the doping and hole concentrations can be estimated from room temperature resistivity measurements. ~ I )

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The influence of He+ implantation on the properties of crystalline silicon solar cells has been investigated. The implantation of 550 keV He+ ions into the masked surface of solar cells was used to form a two-dimensional defect layer inside the cell space-charge region. For suitable implantation doses it is possible to increase the photocurrent without degenerating the values for open circuit voltage thus resulting in an improved efficiency of the cells.