Morphology and Boron Doping Control of Germanium Nanowires by Ex Situ Diffusion Doping

Inasmuchas germanium (Ge) possesses a higher hole mobilitythanthat of silicon, its nanowire structures are anticipated to have significantpotential for use in next-generation transistors. It is, therefore,crucial to control and evaluate impurity doping in Ge nanowires (GeNWs)for the realization of next-generation GeNW-based transistors. DopingGeNWs with boron (B) during the growth process resulted in more taperedsurfaces at higher B-doping concentrations. To prevent the formationof the tapered shape of the GeNWs, a B-doping layer was depositedon the surface of GeNWs after its growth process for the ex situ diffusionB-doping. Afterward, an Al2O3 layer was depositedon the surface of nanowires using an atomic layer deposition method.The ex situ B-doped GeNWs coated with the Al2O3 layer showed an improved thermal stability and a relatively highB-doping concentration. In this study, the B-doping process, electricalactivation of B, and thermal stability of GeNWs were evaluated usingin situ high-temperature X-ray diffraction and Raman spectroscopy.In addition, the electronic transport properties of GeNW with a highB-doping concentration and a cylindrical shape were evaluated.