Geometry Controlled White Light Emission and Extraction in CdS/Black-Si Conical Heterojunctions

The light emission characteristics of Si nanocrystallites on a chemically etched black-Si surface, coupled with its excellent light extraction feature of nanocone geometry is reported for potential use in future Si-based CMOS-compatible light-emitting applications. As a proof of concept, n-CdS/p(+)-black-Si conical-heterojunction arrays, fabricated by depositing n-CdS film on vertically standing nanoporous Si nanocones, exhibiting intense white light emission, have been studied. Si nanocone arrays of 1 to 3 mu m height were fabricated using a metal-assisted chemical etching technique followed by CdS deposition by pulsed laser deposition. A broad EL emission covering the entire visible spectrum and extending up to the NIR wavelength region (450 to 860 nm) has been achieved at room temperature and low forward bias condition. Improved light extraction characteristics in the nanocone textured geometry of black Si over a planar heterojunction have been corroborated by optical simulation analysis. The enhanced light emission characteristics of n-CdS/p(+)-black-Si conical-heterojunction arrays at a low bias voltage may open up a new opportunity for CMOS-compatible, low-power-consuming, and highly efficient phosphor-free white LEDs in the near future.