Improved internal quantum efficiency in high-quality BaSi2 films grown by molecular beam epitaxy

A new method has been developed for the formation of undoped BaSi₂ absorption layers on an Sb-doped n⁺-BaSi₂/p⁺-Si tunnel junction (TJ) formed on Si(111). The diffusion of Sb atoms from the n⁺-BaSi₂ layer was effectively suppressed by inserting a thin Si layer between the n⁺-BaSi₂ and 400-nm-thick undoped BaSi₂ layers. The inserted Si layer was firstly deposited at room temperature, followed by annealing at 650°C by solid phase epitaxy (SPE). Both X-ray diffraction (XRD) and reflection high-energy electron diffraction (RHEED) patterns indicated the good crystalline quality of undoped BaSi₂ overlayers; the I-V characteristics revealed the excellent tunneling effect of the TJ. The photoresponsivity has been greatly improved by the new growth method and reached a maximum of 0.37 A/W at 1.55 eV under a bias voltage of 2 V; the corresponding external quantum efficiency (EQE) and internal quantum efficiency (IQE) increased up to 60% and 70%, respectively, which is the highest value ever reported for semiconducting silicides.