Effects of the implantation of oxygen, nitrogen, and carbon on the density of states of n-type hydrogenated amorphous silicon

The changes in the density of states in the mobility gap g(E) of hydrogenated amorphous silicon (a-Si:H) after the ion implantation of oxygen, nitrogen, and carbon impurities have been examined using a variety of junction capacitance methods. These include deep-level transient spectroscopy, transient voltage-pulse photocapacitance, and drive-level capacitance profiling. Fourier-transform infrared spectroscopy was also employed to evaluate the corresponding changes in bonding that occurred as a result of the implantation. After oxygen implantation with a dose greater than ${10}^{12}$ ${\mathrm{cm}}^{\mathrm{-}2}$ we observed the addition of a distinct defect band to g(E) located approximately 0.7 eV below the conduction-band mobility edge, $E_c$. Some evidence of an additional defect band at $E_c$-0.85 eV was also obtained as a result of nitrogen implantation with doses greater than about 3×${10}^{13}$ ${\mathrm{cm}}^{\mathrm{-}2}$. Carbon-implanted films showed no evidence of any distinct impurity-related defect band, although significant broadening of the intrinsic deep-defect band was observed.