P-doped germanium nanowires with Fano-broadening in Raman spectrum

The optimized growth conditions for high density germanium (Ge) nanowires and P-doped Ge nanowires on Si (111) substrate were investigated, the phosphorus (P)-doping in Ge nanowires was also characterized. Vapor liquid solid-low pressure chemical vapor deposition (VLS-LPCVD) of Ge nanowires was conducted with different thicknesses of Au film as catalyst, different flow rates of GeH4 as precursor and PH3/Ar as co-flow. The morphologies of the Ge nanowires were characterized by scanning electron microscopy (SEM), the P-doping was verified by micro Raman spectroscopy via measuring the P local vibrational peak (342-345 cm-1) and asymmetric broadening of Ge-Ge vibrational peak (about 300 cm-1), respectively. The characterization results show that 1 nm thickness of Au catalyst is the most suitable condition among thicknesses of 0.1, 1, 5, and 10 nm for the growth of high density Ge nanowires at 300 and 350 °C, and 0.5 sccm is the best flow rate of PH3/Ar to grow high density and large scale P-doped Ge nanowires among flow rates of 0.5, 1 and 2 sccm. The P impurity can be doped into Ge nanowires effectively during LPCVD process at 350 °C.