Si/Si_1-xGe_x/Si Heterojunction PIN nanowires fabricated by using an aqueous electroless etching method

The p⁺ poly-silicon/silicon-germanium/n⁺ single-crystal silicon (Si/Si_1-xGe_x/Si) PIN heterojunction nanowires (NWs) were fabricated by using the aqueous electroless etching (AEE) method. The synthesized NWs were highly aligned in the vertical direction with uniform lengths of approximately 5 μm. Three distinguishable peaks of Si_1-xGe_x (400), with values of x corresponding to 11.8, 16.8, and 22.2%, were clearly observed in the X-ray diffraction (XRD) pattern for the NW structures, which confirms that heterojunction NWs were successfully synthesized. Noticeably, the photo response of the photodiodes (PDs) fabricated using the heterojunction NWs was greatly increased compared to that of the bulk-based PDs. Specifically, a dramatic decrease in the dark current by three orders of magnitude was observed for the heterojunction NW-based PDs. Thus, a clear distinction of four orders of magnitude between the off-currents under the dark and light conditions was observed in the reverse bias region for the NW-based PDs whereas in bulk-based PDs the current levels differed by less than one order of magnitude.