Doping of β-FeSi2 films with boron and arsenic by sputtering and its application for optoelectronic devices

We fabricated impurity-doped β-FeSi2 thin films with boron as p-type and arsenic as n-type dopants by sputtering method. The doping source materials were elemental boron chips and heavily arsenic-doped Si chips. They were put on two separate silicon targets and were co-sputtered with silicon during Fe/Si multilayer deposition. For boron-doped p-type β-FeSi2 films, microstructures were affected by the temperature decrease rate after annealing at 800 °C, and cracks were observed when the temperature decrease rate was high as 20 °C/min. It was found that cracks were eliminated by slow cooling at the rate of 2 °C/min. By changing boron concentration, net hole concentration from 3.0 × 1017 to 1.0 × 1019 cm−3 and Hall mobilities from 100 to 20 cm2/Vs were successfully achieved. SIMS measurements showed homogeneous distribution of boron dopant in β-FeSi2 film. For arsenic-doped n-type β-FeSi2 films, the activation of arsenic dopant requested longer annealing time at 800 °C than for boron. The microstructures were independent on the cooling rate after annealing. The doping level of net electron concentration from 2.0 × 1017 to 4.0 × 1017 cm−3 and mobility from 250 to 160 cm2/Vs were obtained when the arsenic concentration was changed from about 1.2 × 1018 to 3.2 × 1018 cm−3. β-FeSi2 thin film p/n homojunctions were formed by successive deposition of p- and n-type β-FeSi2 films on Si substrates in the same sputtering chamber. The diodes showed rectifying I-V characteristics and photoresponse to 1.3-1.6 μm near-infrared light.