Polypeptoids brush layers for the deterministic doping of semiconductors

Introduction To move in the way of nanoelectronics, polymers can be employed for the scaling down of transistors by modulating the doping of semiconductors. Many methodologies have been explored to precisely introduce dopant atoms inside a semiconductor. Among them “monolayer doping” holds a special position as the density of doping atoms is controlled by the steric hindrance of the dopant containing carrier molecules. Polystyrene and poly-(methyl methacrylate) with a terminal phosphate moiety and narrow dispersity, have been used to dope silicon substrate but the effect of polydispersity is still a challenge. Therefore, monodisperse polypeptoid dopants with a phosphorus containing moiety a one end were synthesized by solid phase sub-monomer synthesis (SPSS) and employed to precisely control the dopant atom amount. Methodology Two sets of polypeptoids were synthesized either containing phenyl lateral chains consisting of 5, 10, 14 and 19 monomer units or containing 10 monomer units with linear lateral chains of different length. The polypeptoids were grafted on a silicon substrate by hot plate at different temperature. Finally, the phosphorus dose at the silicon surface was determined by TOF SIMS analysis. Results and discussion The synthesized polymers exhibited a dispersity near to one as determined by MALDI TOF analysis. The suitable conditions for grafting to the silicon wafer by thermal annealing were determined to be 190°C for 40 s. Finally, an inverse correlation was found between the phosphorus dose determined by TOF SIMS and the polypeptoid length or lateral steric hindrance.