A SiGe alloy grown on Si was successfully hyperdoped with S. The results indicate successful resolidification and dopant incorporation and the formation of a p-n junction. Prototype photodetectors exhibit limited sub-band gap photoresponse.

Recently, hyperdoped Si has gained interest as an infrared material for photodetectors due to the possible formation of intermediate bands inside the Si band gap. In particular, Au-hyperdoped Si has been demonstrated to exhibit a sub-band gap photoresponse, but efficiencies remain low. To achieve high efficiency Au-hyperdoped Si (Si:Au) photo devices, we develop a recipe for Ohmic contact to Si:Au materials by understanding the properties of the interfacial region. In this work, we show that Si:Au can form an Ohmic contact, which is relatively independent of the contacting metal due to Fermi pinning behavior. Degenerate boron doping decreases the contact resistivity by 1 order of magnitude, because the Si:Au resistivity decreases immediately below the contact. Cr/Ni/Au 5/200/200 nm metal stacks with boron doping exhibit the lowest specific contact resistivity (0.16 Omega & sdot;cm2) in this work, better than Au-based contacts. We also demonstrate that the Cr silicide formation temperature causes the relocation of Au atoms and degrades sub-band gap behavior.

The performance of hyperdoped silicon-based solar cells and photodetectors synthesized via ion implantation and pulsed laser melting can be enhanced by improving the fabrication process. Considering silicon self-implant as a model system, we show that there are two ways to reduce ion implantation defects and improve material quality: (1) increasing the pulsed laser melting depth and (2) introducing a pre-annealing step. This leads to improved charge carrier lifetimes and mobilities. We apply the pre-annealing method to tellurium- and gold-hyperdoped silicon samples and test the charge-carrier dynamics at two excitation wavelengths. After pre-annealing, for silicon self-implanted samples and tellurium-hyperdoped silicon samples, the carrier lifetime improves beyond our experimental detection limit (>4 ns) and a limited lifetime improvement is observed in gold-hyperdoped silicon. The improvement of mobility in silicon self-implanted sample is 1.3 times higher, two times higher in tellurium-hyperdoped silicon, and 1.1 times higher in gold-hyperdoped silicon after 350 °C pre-annealing. The improvement in carrier lifetime and mobility in Si:Te follows our model system, but the limited improvement in Si:Au suggests that dopant–defect interactions might limit the benefits of pre-annealing. Our study also shows that incorporating one additional step in the fabrication process can enhance carrier transport in hyperdoped-silicon-based solar cells and photodetectors.

Hyperdoping Si with transition metals to form intermediate bands for infrared absorption has attracted attention recently for producing sub-bandgap photoconductivity. In particular, Si hyperdoped with Au has been demonstrated to exhibit optoelectronic response at 1550 nm. However, the reported external quantum efficiencies (EQEs) are low, and the device fabrication processes had not been optimized. In this paper, we demonstrate a significant improvement in sub-bandgap EQE through modification of the material and device fabrication processes. By increasing the Si:Au layer thickness, modification of device design, and formation of Ohmic contacts, the EQE was measured to be as high as 0.44% at 1550 nm, nearly two orders of magnitude higher than previous reports from similar devices. Additionally, the EQE was measured to be in the 10-3 range for wavelengths as long as 2.4 μm. The EQE spectrum showed features that were attributed to defect levels from a substitutional Au acceptor defect. The above bandgap EQE showed gain in one device. Thermal annealing at 300 °C does not improve the efficiency of Si:Au photodiodes. These results demonstrate the viability of Au-hyperdoped Si for infrared detection below the bandgap of Si.

Hyperdoped Si materials extend Si response range into near infrared by forming intermediate band in Si band gap. Ti hyperdoped Si (Si:Ti) has been demonstrated to have subbandgap photo response. In this work, we fabricated and characterized Si:Ti photodiodes and optimized the structure. At room temperature, the 3.5×10-3 EQE has been obtained at telecommunication wavelength 1550nm. And the detectable response extends until 2250nm. The results show the potential of Si:Ti materials being both Si:Ti photovoltaics and commercialized IR detection. To improve the efficiency of Si:Ti photodetectors, the affection of absorption rate, devices structure and the Si:Ti crystal quality is discussed.

Waveguides fabricated from GeSn alloys have recently demonstrated lasing at cryogenic temperatures, but room temperature operation has yet to be achieved. In this work, we model the effects of propagation loss, mirror reflection, Sn content, and recombination lifetime on the lasing threshold at room temperature.

Incorporating ultrahigh concentrations of deep-level dopants in silicon drastically alters silicon’s optoelectronic properties. Photodiodes built from silicon hyperdoped with gold extend light sensitivity into the shortwave infrared region, far beyond the absorption edge of a pristine silicon sample. Deep-level dopants, however, also enhance carrier recombination; even though hyperdoped silicon has great light absorption properties, short charge carrier lifetime limits its applications. In this work, using terahertz spectroscopy, we investigate the charge carrier lifetime of gold–hyperdoped silicon, where the gold dopants are introduced by either film deposition or ion implantation, followed by pulsed laser melting. Using reactive ion etching, we measure how carrier lifetime changes when dopant concentration profiles are altered. Furthermore, using a 1D diffusion and recombination model, we simulate carrier dynamics when electrons are excited by sub-bandgap light. Our results show that the dopant distribution profile heavily influences excited carrier dynamics. We found that etching improves the half-life by a factor of two. In the short-wave-infrared range, the gold dopants are both light absorption centers and recombination centers. Focusing on optoelectronic properties in the short-wave-infrared region, our results suggest that these samples are over doped—etching much of the gold dopants away has little impact on the number of excited electrons at a later time. Our results suggest that dopant profile engineering is important for building efficient optoelectronic devices using hyperdoped semiconductors.

Waveguides were fabricated from highly n-type doped GeSn layers with Sn content at 5.4%–6.2% and grown on Ge-buffered Si substrates. The waveguides were optically pumped using a 976 nm continuous-wave laser, and the waveguide emission spectrum was collected and analyzed. The results indicate a non-linear power increase via higher injection-level at room temperature. Comprehensive theoretical models for the waveguide emission power dependence were developed to reproduce experimental data and provide an understanding of the nonlinear power dependence.

We report an investigation on the photo-response from a GeSn-based photodetector using a tunable laser with a range of incident light power. An exponential increase in photocurrent and an exponential decay of responsivity with increase in incident optical power intensity were observed at higher optical power range. Time-resolved measurement provided evidence that indicated monomolecular and bimolecular recombination mechanisms for the photo-generated carriers for different incident optical power intensities. This investigation establishes the appropriate range of optical power intensity for GeSn-based photodetector operation.

We demonstrate a single-layer THz metadevice that exhibits cross polarization transmission, a key factor to achieve optical activity. The device is comprised of a two-dimensional array of split ring resonators, each with a vanadium oxide (VO 2 ) pad, integrated into one of the two capacitive gaps of the unit cell. Through numerical investigations we find that as the conductivity of VO 2 increases the amplitude of the cross-polarization intensity decreases but maintains a wider broadband range than previously reported for single layered hybrid metamaterial (MM) devices as the VO 2 transforms from the insulator to metallic phase. Also the asymmetric transmission, optically modulated by the device, is higher than that of multi-layered MM devices. Due to the materials properties of VO 2 , our results introduce a promising method that allows for an active sub-cycle dynamic tunability for THz polarization conversion with multiple modalities using optical, electrical or thermal switching. The study is an important step forward in developing compact, integrated, passive and active metadevices for polarization and wavefront control application in the THz.

Atom Probe Tomography (APT) is used to explore Si into which a high concentration of Ti has been incorporated through ion implantation and pulsed laser melting. Ti shows abundant segregation out of the Si, with regions near the surface showing evidence of the classic "cellular breakdown" morphology characteristic of constitutional supercooling. Ti concentrations in excess of the nominal Mott limit have previously been reported, but these concentrations have relied on secondary ion mass spectrometry (SIMS) measurements, which are susceptible to artifacts. The APT method provides improvements over the SIMS method and shows that Ti concentrations are below the Mott limit everywhere outside of the broken-down regions below the surface SiO layer. The data confirm that Ti behaves as would be expected under a conventional rapid solidification theory. This has implications for how Ti in Si concentration data produced by non-atomistic techniques are interpreted and also indicates that the use of the conventional solidification apparatus can be used to predict Ti concentrations that may be achievable using implantation and laser melting techniques.

Direct-bandgap germanium-tin (Ge-Sn) alloys are highly sought-after materials for applications in silicon photonic integrated circuits. Other than crystal quality, two main factors determine the transition from the indirect to direct bandgap: the high Sn concentration and the strain relaxation in the materials. Using ion implantation and pulsed laser melting, we demonstrate a fully-relaxed Ge-Sn alloy with a Sn concentration of 6at. %. This concentration is at least 10 times higher than the equilibrium solubility of Sn in Ge. Cross-sectional transmission electron microscopy shows unconventional threading-like defects in the film as the mechanism for the strain relaxation. Due to the high degree of strain relaxation and the good crystal quality, photoluminescence could be obtained from the samples to examine the indirect-direct bandgap transition in the alloys.

Ge-Sn alloys with a sufficiently high concentration of Sn is a direct bandgap group IV material. Recently, ion implantation followed by pulsed laser melting has been shown to be a promising method to realize this material due to its high reproducibility and precursor-free process. A Ge-Sn alloy with ~9 at.% Sn was shown to be feasible by this technique. However, the compressive strain, inherently occurring in heterogeneous epitaxy of the film, evidently delays the material from the direct bandgap transition. In this report, an attempt to synthesize a highly-relaxed Ge-Sn alloy will be presented. The idea is to produce a significantly thicker film with a higher implant energy and doses. X-ray reciprocal space mapping confirms that the material is largely-relaxed. The peak Sn concentration of the highest dose sample is 6 at.% as determined by Rutherford backscattering spectrometry. Cross-sectional transmission electron microscopy shows unconventional defects in the film as the mechanism for the strain relaxation. Finally, a photoluminescence (PL) study of the strain-relaxed alloys shows photon emission at a wavelength of 2045 nm, suggesting an active incorporation of Sn concentration of ~6 at.%. The results of this study pave way to produce high quality relaxed GeSn alloy using an industrially scalable method.

Room temperature photoluminescence (PL) was observed from GeSn layers fabricated by ion implantation of Sn into bulk Ge followed by pulsed laser melting using an Nd:YAG laser at 355 nm. PL measurements indicate regions of high-crystalline quality with Sn concentrations of up to 9%.

Traditional lattice-induced transparency demonstrations are activated by varying the meta-atom lattice constant such that the plasmonic and lattice modes interfere. Here we report on the observation of enhanced coupling between two eigenmodes (first-and second-order) by varying the lattice parameter in a symmetric split ring resonator design. The higher-order quasi-dark mode blueshifts, introducing strong coupling with the fundamental bright mode for periods above 345 mu m. Numerical simulations are verified experimentally and supplemented with a two-oscillator model showing good agreement. Furthermore, larger positive group delay values are achieved in the vicinity of the transparency window with minimal absorption, indicating a strong potential for slow light applications. (C) 2019 Optical Society of America