We report room-temperature operation of 1 × 1 cm2 infrared photoconductive photodetectors based on silicon supersaturated with titanium. We have fabricated these Si-based infrared photodetectors devices by means of ion implantation followed by a pulsed laser melting process. A high sub-band gap responsivity of 34 mV W−1 has been obtained operating at the useful telecommunication applications wavelength of 1.55 μm (0.8 eV). The sub-band gap responsivity shows a cut-off frequency as high as 1.9 kHz. These Si-based devices exhibit a non-previous reported specific detectivity of 1.7 × 104 cm Hz1/2 W−1 at 660 Hz, under a 1.55 μm wavelength light. This work shows the potential of Ti supersaturated Si as a fully CMOS-compatible material for the infrared photodetection technology.

Hyperdoping silicon, which introduces deep-level dopants into Si at concentrations near one atomic percent, drastically changes its optoelectronic properties. We review recent progress in the fundamental understanding of the material properties and state of the art sub-bandgap infrared photodetectors. Different hyperdoping techniques are reviewed and compared, namely ion implantation followed by pulsed laser melting (PLM) or other fast annealing methods and PLM of Si with a dopant precursor. We review data available in the literature for material properties related to the success of optoelectronic devices such as the charge carrier lifetime, mobility, and sub-bandgap light absorption of hyperdoped Si with different dopants. To maximize carrier generation and collection efficiency in a sub-bandgap photodetector, charge carrier lifetimes must be long enough to be transported through the hyperdoped layer, which should be on the order of light absorption depth. Lastly, the charge transport properties and photodetector responsivities of hyperdoped Si based photodiodes at room temperature and at cryogenic temperatures are compared. The charge carrier transport mechanisms at different temperature ranges and in different dopant systems are discussed. At room temperature, despite different dopant energetics and hyperdoped thicknesses, light detection exhibits similar spectral responsivities with a common cutoff around 0.5 eV, and at low temperatures, it extends further into the infrared range. The roles of the dopant energetics and process-induced defects are discussed. We highlight future material development directions for enhancing device performance.

We have analyzed the increase of the sheet conductance (ΔG□) under spectral illumination in high dose Ti implanted Si samples subsequently processed by pulsed-laser melting. Samples with Ti concentration clearly above the insulator-metal transition limit show a remarkably high ΔG□, even higher than that measured in a silicon reference sample. This increase in the ΔG□ magnitude is contrary to the classic understanding of recombination centers action and supports the lifetime recovery predicted for concentrations of deep levels above the insulator-metal transition.

We have analyzed the spectral sub-bandgap photoresponse of silicon (Si) samples implanted with vanadium (V) at different doses and subsequently processed by pulsed-laser melting. Samples with V concentration clearly above the insulator-metal transition limit show an important increase of the photoresponse with respect to a Si reference sample. Their photoresponse extends into the far infrared region and presents a sharp photoconductivity edge that moves towards lower photon energies as the temperature decreases. The increase of the value of the photoresponse is contrary to the classic understanding of recombination centers action and supports the predictions of the insulator-metal transition theory.

Intermediate band formation on silicon layers for solar cell applications was achieved by titanium implantation and laser annealing. A two-layer heterogeneous system, formed by the implanted layer and by the un-implanted substrate, was formed. In this work, we present for the first time electrical characterization results which show that recombination is suppressed when the Ti concentration is high enough to overcome the Mott limit, in agreement with the intermediate band theory. Clear differences have been observed between samples implanted with doses under or over the Mott limit. Samples implanted under the Mott limit have capacitance values much lower than the un-implanted ones as corresponds to a highly doped semiconductor Schottky junction. However, when the Mott limit is surpassed, the samples have much higher capacitance, revealing that the intermediate band is formed. The capacitance increasing is due to the big amount of charge trapped at the intermediate band, even at low temperatures. Ti deep levels have been measured by admittance spectroscopy. These deep levels are located at energies which vary from 0.20 to 0.28 eV below the conduction band for implantation doses in the range 10¹³-10¹⁴ at./cm². For doses over the Mott limit, the implanted atoms become nonrecombinant. Capacitance voltage transient technique measurements prove that the fabricated devices consist of two-layers, in which the implanted layer and the substrate behave as an n⁺/n junction.