Mid-IR-Sensitive n/p-Junction Fabricated on p-Type Si Surface via Ultrashort Pulse Laser n-Type Hyperdoping and High-Temperature Annealing

The mid-infrared (IR)-sensitive n/p-junction was fabricated on a p-doped silicon (Si) wafer via ultrashort laser n-type surface hyperdoping and high-temperature annealing. First, the n-type sulfur hyperdoping regimes were studied by 0.3 ps IR (1030 nm) laser nanopatterning of Si surfaces covered by a millimeter-thick liquid carbon disulfide layer. The nanopatterned sub-micron thick Si surface layers demonstrate high exposure-tunable near-IR (NIR)–mid-IR (MIR) optical density and related high (∼1 at. %) contents of sulfur, carbon, and oxygen, with their abundance and chemical states visualized by cross-sectional energy-dispersive spectroscopy and X-ray photoelectron spectroscopy, respectively. Their spatially inhomogeneous phase and structural features were characterized by high-resolution transmission electron microscopy, electron diffraction, and micro-Raman spectroscopy. High-temperature annealing (30 min) of the nanopatterned sub-micron thick Si surface layers in ambient air at 1150 °C and the following slow or fast quenching result in partial oxidation of the top amorphous layer. Upon oxide film delamination, the surface n/p-junction appears with the high sulfur-doping level (≈0.5 at. %) and related NIR–MIR optical density and n-type conductivity with high free-electron concentration and mobility. This innovative laser-hyperdoping technology and the resulting promising characteristics of the annealed Si layers open a way for revisiting the established CMOS-compatible technology for IR-sensitive solar cell, thermal imaging, and night-vision device fabrication.