Tunable photoluminescence from nc-Si/a-SiN_x:H quantum dot thin films prepared by ICP-CVD

摘要

Intense visible photoluminescence (PL) tunable within 1.66-2.47 eV, under UV 325 nm excitation, was obtained from nanocrystalline silicon quantum dots (~ 5.72-1.67 nm in diameter) embedded in amorphous silicon-nitride matrix (nc-Si/a-SiN_x:H) prepared in RF-ICPCVD (13.56 MHz) at substrate temperatures between 400 to 150 °C. The dominant component of PL, having a narrow band width of ~ 0.16-0.45 eV, originates from quasi-direct band-to-band recombination due to quantum confinement effect (QCE) in the nanocrystalline silicon quantum dots (nc-Si QDs) of appropriate size; however, the contribution of defects arose at lower substrate temperatures leading to asymmetric broadening. Intense atomic hydrogen flux in high-density inductively coupled plasmas (ICPs) provides a very high surface coverage, passivates well the nonradiative dangling bonds, and thereby favors the PL intensity. The average size of nc-Si QDs measured by HR-TEM appears consistent with similar estimates from Raman studies. The red shift of the Raman line and corresponding line broadening originates from the confinement of optical phonons within nc-Si QDs. Photoluminescence emerging from nc-Si/a-SiN_x:H quantum dots obtained from the low temperature and single-step plasma processing holds great promise for the fabrication of light-emitting devices and flexible flat panel displays.