Researchers have fabricated a single-crystalline selenium-hyperdoped silicon photodetector operating at room temperature to detect short-wavelength infrared light. Utilizing flash-lamp annealing instead of laser methods, the technology suppresses impurity segregation, achieves an effective electron concentration of up to (2.8 ± 0.7) × 1020 cm−3, and improves industrial sorting and inspection capabilities.
Fabrication and Annealing of Selenium-Hyperdoped Silicon Layers
The fabrication process begins with double-side polished 100 p-type silicon substrates carrying a resistivity of 1 to 10 ohm centimeters. These substrates undergo room-temperature selenium ion implantation at fluences of 3 × 1015 cm−2, 6 × 1015 cm−2, and 9 × 1015 cm−2 with an implantation energy of 60 keV. This procedure yields a projected range of 50 nanometers alongside atomic selenium concentrations of roughly 1.1 percent, 2.3 percent, and 3.5 percent, as verified by Rutherford backscattering spectrometry measurements.
To recrystallize the amorphized material, researchers apply flash-lamp annealing in a nitrogen atmosphere utilizing an energy density of 33 joules per square centimeter for 1.3 milliseconds. A preheating step at 300 degrees Celsius for 30 seconds precedes the annealing to mitigate internal strain. In contrast to liquid phase epitaxy driven by laser methods, this solid phase annealing technique induces single-crystalline hyperdoped silicon free from extended defects while suppressing selenium segregation and diffusion.
Microstructural Properties and Lattice Integration
Micro-Raman spectroscopy confirms the elimination of amorphous damage following the flash-lamp treatment. Virgin single-crystalline silicon exhibits a sharp transverse optical phonon mode peak at 520 cm−1 alongside a second-order transverse acoustic phonon scattering peak at 303 cm−1. The as-implanted samples show a broad band centered around 460 cm−1 attributable to ion-induced amorphization. Subsequent to annealing, only the sharp 520 cm−1 band remains, proving full recrystallization of the implanted layer.
High-angle annular dark-field scanning transmission electron microscopy combined with energy-dispersive X-ray spectroscopy mapping demonstrates a uniform selenium distribution spanning approximately 50 nanometers in width. Unlike gold-hyperdoped silicon synthesized through pulsed laser melting, the flash-lamp-processed material displays no surface segregation and no nanoscale selenium agglomerates despite high dopant concentrations. Channeling spectra further reveal a substitutional fraction of approximately 70 percent, with a near-surface minimum backscattered yield of about 4 percent.
Electrical Characteristics and Infrared Detection Performance
Room-temperature Hall effect measurements performed in van der Pauw geometry characterize the electrical properties of the hyperdoped layers. The samples achieve effective electron concentrations reaching (8.1 ± 0.7) × 1019 cm−3 for the 1.1 percent selenium concentration, (3.6 ± 0.7) × 1020 cm−3 for the 2.3 percent concentration, and (2.8 ± 0.7) × 1020 cm−3 for the 3.5 percent concentration. These values surpass the solid solubility limit of selenium in silicon by four orders of magnitude.
This electronic profile enables room-temperature operation as a short-wavelength infrared photodetector. Integrating these hyperdoped silicon layers bridges the gap between conventional silicon detectors and expensive compound semiconductor alternatives, offering extended spectral sensitivity without the need for cryogenic cooling systems.
Industrial Applications in Sorting and Inspection
Advanced infrared detection technologies leverage distinct optical absorption and reflection profiles across specific spectral bands to perform industrial sorting and non-destructive quality checks. Water strongly absorbs radiation at 1,450 nanometers, rendering moisture-rich areas dark in captured images. This principle allows systems to detect bruises and dents on the surface of agricultural produce like apples during high-speed sorting.
Beyond agriculture, short-wavelength infrared imaging penetrates opaque packaging materials to inspect internal product integrity. Manufacturers utilize these wavelengths to identify pinching errors in sealed food containers, distinguish black-colored contaminants from black beans, and detect fine strands of hair on processed food items. Sorting facilities also apply multi-spectral processing to separate cotton from synthetic polyester fibers regardless of their visible color.
