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

Inasmuch as germanium (Ge) possesses a higher hole mobility than that of silicon, its nanowire structures are anticipated to have significant potential 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. Doping GeNWs with boron (B) during the growth process resulted in more tapered surfaces at higher B-doping concentrations. To prevent the formation of the tapered shape of the GeNWs, a B-doping layer was deposited on the surface of GeNWs after its growth process for the ex situ diffusion B-doping. Afterward, an Al2O3 layer was deposited on 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 high B-doping concentration. In this study, the B-doping process, electrical activation of B, and thermal stability of GeNWs were evaluated using in situ high-temperature X-ray diffraction and Raman spectroscopy. In addition, the electronic transport properties of GeNW with a high B-doping concentration and a cylindrical shape were evaluated.