Ga-doping for β-FeSi2 films prepared by molecular beam epitaxy

β-FeSi2 is expected as a new material for light emitting diode and optical sensor operating at 1.5 μm. However, doping techniques suited for various fabrication methods of β-FeSi2 films have not been established. In this report, we present the results of Ga doping as a p-type impurity into β-FeSi2 films using three molecular beam epitaxy (MBE)-associated growth methods. They are, (i) standard MBE method by depositing simultaneously Fe, Si and Ga molecular beams, (ii) alternating Fe/Si multilayers deposition method with an interval time between the Fe and Si depositions (migration enhanced epitaxy, MEE) in which Ga was deposited only in Si layer, (iii) standard alternating Fe/Si multilayers deposition (superlattice, SL) method in which Ga was deposited only in Si layer. All β-FeSi2 films were prepared on Si substrates at room and elevated temperatures in MBE chamber and were subjected to post-annealing. Ga concentration was adjusted by changing its Knudsen effusion cell temperature or opening time of shutter for K-cell. Unintentionally doped β-FeSi2 films prepared by SL method were n-type, having residual net electron concentration, ∣ND-NA∣ of ∼3 × 1016 cm−3 and mobility of ∼400 cm2/V s. When these β-FeSi2 films were doped with Ga above a critical concentration, they exhibited p-type conductivity. By varying Ga concentration, net hole concentration, ∣NA-ND∣ ranging from 7 × 1016 to 2 × 1018 cm−3 with hole Hall mobility, μh from 200 to 10 cm2/V s were obtained. These results demonstrate that Ga is an effective p-type dopant for β-FeSi2 films to fabricate various electronic and optoelectronic devices.