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

We fabricated impurity-doped beta-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 beta-FeSi2 films, microstructures were affected by the temperature decrease rate after annealing at 800 degrees C, and cracks were observed when the temperature decrease rate was high as 20 degrees C/min. It was found that cracks were eliminated by slow cooling at the rate of 2 degrees C/min. By changing boron concentration, net hole concentration from 3.0 x 10(17) to 1.0 x 10(19) cm(-3) and Hall mobilities from 100 to 20 cm(2)/Vs were successfully achieved. SIMS measurements showed homogeneous distribution of boron dopant in beta-FeSi2 film. For arsenic-doped n-type beta-FeSi2 films, the activation of arsenic dopant requested longer annealing time at 800 degrees C than for boron. The microstructures were independent on the cooling rate after annealing. The doping level of net electron concentration from 2.0 x 10(17) to 4.0 x 10(17) cm(-3) and mobility from 250 to 160(2)cm/Vs were obtained when the arsenic concentration was changed from about 1.2 x 10(18) to 3.2 x 10(18) cm(-3). beta-FeSi2 thin film p/n homojunctions were formed by successive deposition of p- and n-type beta-FeSi2 films on Si substrates in the same sputtering chamber. The diodes showed rectifying I-V characteristics and photoresponse to 1.3-1.6 mu m near-infrared light. (c) 2004 Elsevier B.V. All rights reserved.