Highly efficient and stable luminescence of nanocrystalline porous silicon treated by high-pressure water vapor annealing

The effects of a treatment based on high-pressure water vapor annealing (HWA) on nanocrystalline porous silicon have been investigated in terms of the photoluminescence (PL) efficiency and stability. For originally nonluminescent samples with a relatively low porosity, the treatment produces highly efficient and stable luminescent nanocrystalline-Si (nc-Si) layers without affecting the emission wavelength. Under appropriate conditions of pressure (2.6 MPa) and temperature (260 °C), the PL external quantum efficiency reaches 23% at room temperature. Electron-spin-resonance and infrared absorption analyses show that the HWA treatment promotes surface oxidation of nc-Si under a minimized mechanical stress and consequently generates sufficiently passivated nc-Si∕SiO2 interfaces with an extremely low nonradiative defect density. This causes a drastic enhancement in the PL efficiency associated with a strong localization of excitons in nc-Si. As a practical approach, the HWA technique is very useful for fabrication of efficient and stable optoelectronic nc-Si devices.