Solid-state diffusion as an efficient doping method for silicon nanowires and nanowire field effect transistors

In this work we investigate doping by solid-state diffusion from a doped oxide layer, obtained by plasma-enhanced chemical vapor deposition (PECVD), as a means for selectively doping silicon nanowires (NWs). We demonstrate both n-type (phosphorous) and p-type (boron) doping up to concentrations of 1020 cm-3, and find that this doping mechanism is more efficient for NWs as opposed to planar substrates. We observe no diameter dependence in the range of 25 to 80 nm, which signifies that the NWs are uniformly doped. The drive-in temperature (800-950 deg. C) can be used to adjust the actual doping concentration in the range 2 x 1018 to 1020 cm-3. Furthermore, we have fabricated NMOS and PMOS devices to show the versatility of this approach and the possibility of achieving segmented doping of NWs. The devices show high Ion/Ioff ratios of around 107 and, especially for the PMOS, good saturation behavior and low hysteresis.