Characterization of phosphorus and boron heavily doped LPCVDpolysilicon films in the temperature range 293-373 K

In this paper, thermal properties of phosphorus and boron-doped low pressure chemical vapor deposition (LPCVD) polysilicon layers with regard to sensor applications are presented. Thermoelectric coefficient and relative resistance variations of polysilicon are investigated within the temperature range of 293-373 K. Test structures and characterization benches have been developed to obtain measurements with precision of 5%. Ion implantation has been experimented to achieve low electrical resistivities and high Seebeck coefficients. It can be seen that the temperature coefficient of resistance of doped polysilicon is negative, approaches zero, or positive depending on the doping concentration. These results are, to our knowledge, the first reported for such dopant concentrations and are important for design and optimization of high sensitivity thermal sensors using n- and p-doped-LPCVD polysilicon thermopile     

Photoconductivity of Hf-based binary metal oxides

In order to explore the possibility of bandgap engineering in binary oxide insulators we studied photoconductivity of nanometer-thin Hf oxide layers containing different fractions of cations of another sort (Si, Al, Sr, or Ce) deposited on (1 0 0)Si. The smallest bandgaps of the Hf:Al and Hf:Ce oxides are close to the values found in elemental Al₂O₃ (6-6.2 eV) and HfO₂ (5.6 eV), respectively, and show little sensitivity to the concentration of Al or Ce. This result suggests that the oxide sub-network with the largest bandgap preserves its gap energy, while development of a narrower gap is prevented, likely, by dilution of the second cation sub-network. In Hf:Si oxide samples photoconductivity thresholds of 5.6-5.9 eV, corresponding to the bandgap of HfO₂, were observed for all studied Si concentrations, suggesting phaseseparation to occur during deposition. Photoconductivity of SrHfO₃ exhibits two thresholds, at 4.4 and 5.7 eV, which are close to the bandgaps of elemental SrO₂ and HfO₂, respectively. These gap values indicate the phase separation also to occur in this binary oxide. Through this work photoconductivity is demonstrated to be a feasible method to trace phase separation in binary oxides, even in nanometer-thin layers.