The integration in Si technology of highly doped of Ge layers with a controlled amount of strain is crucial for nanoelectronic and photonic applications. N-type doping of Ge layers epitaxially grown on Si by P ion-implantation and pulsed laser melting is reported. In particular, samples with or without a post-growth annealing cycle in order to reduce the amount of threading dislocations (TDs) have been studied, in comparison with bulk Ge. Samples have been characterized by Secondary Ion Mass Spectrometry, Van der Paw-Hall and High-Resolution X-ray Diffraction. A very low out-diffusion, 1 x 10(20) cm(-3) carrier concentration with 100% P activation, as well as an increase of the tensile strain together with an improvement of the crystalline quality is reported, regardless of the as-grown TD density.

Germanium recently attracted a renewed interest for its potential applications in several fields such as nanoelectronics, photonics, plasmonics, etc., but well-known issues about doping at high concentration and controlling impurity profiles prevent its integration in technology. To this purpose, p-type doping aluminum ion implantation followed by pulsed laser annealing in the melting regime has been investigated for the first time. In particular, two different regimes have been studied, in order to explore the limit of incorporation for such a method: 6.4 x 10(14) Al/cm(2) and 4.2 x 10(15) Al/cm(2), both at 25 keV, corresponding to concentrations below and above the solid solubility, respectively. We found that in the former case, oxygen contamination precludes full activation (< 60%), as suggested by Raman characterizations. Besides, secondary ion mass spectrometry evidences pronounced out-diffusion and pile-up of the dopant near the surface. In the letter case, remarkable (similar to 1 x 10(20) Al/cm(3)), although partial (similar to 30%), electrical activation is obtained, independently on O occurrence. Therefore, O-Al and Al-Al clustering are proposed as concurrent mechanisms, limiting full activation at high implanted dose. Nevertheless, the samples display good crystalline quality and, surprisingly, a significant thermal stability (up to 600 degrees C).

Obtaining short-wavelength-infrared (SWIR; 1.4 ?m-3.0 ?m) room-temperature photodetection in a low-cost, group IV semiconductor is desirable for numerous applications. We demonstrate a non-equilibrium method for hyperdoping germanium with selenium or tellurium for dopant-mediated SWIR photodetection. By ion-implanting Se or Te into Ge wafers and restoring crystallinity with pulsed laser melting induced rapid solidification, we obtain single crystalline materials with peak Se and Te concentrations of 1020 cm-3 (104 times the solubility limits). These hyperdoped materials exhibit sub-bandgap absorption of light up to wavelengths of at least 3.0 ?m, with their sub-bandgap optical absorption coefficients comparable to those of commercial SWIR photodetection materials. Although previous studies of Ge-based photodetectors have reported a sub-bandgap optoelectronic response only at low temperature, we report room-temperature sub-bandgap SWIR photodetection at wavelengths as long as 3.0 ?m from rudimentary hyperdoped Ge:Se and Ge:Te photodetectors.

Short-wavelength-infrared (SWIR; 1.4-3.0 ?m) photodetection is important for various applications. Inducing a low-cost silicon-compatible material, such as germanium, to detect SWIR light would be advantageous for SWIR applications compared with using conventional (III-V or II-VI) SWIR materials. Here, we present a scalable nonequilibrium method for hyperdoping germanium with gold for dopant-mediated SWIR photodetection. Using ion implantation followed by nanosecond pulsed laser melting, we obtain a single-crystal material with a peak gold concentration of 3 × 1019cm-3 (103 times the solubility limit). This hyperdoped germanium has fundamentally different optoelectronic properties from those of intrinsic and conventionally doped germanium. This material exhibits sub-band-gap absorption of light up to wavelengths of at least 3 ?m, with a sub-band-gap optical absorption coefficient comparable to that of commercial SWIR photodetection materials. We show that germanium hyperdoped with gold exhibits sub-band-gap SWIR photodetection at room temperature, in contrast with previous doped-germanium photodetector studies, which only show a low-temperature response. This material is a potential pathway to low-cost room-temperature silicon-compatible SWIR photodetection.

Laser Thermal Annealing (LTA) at various energy densities was used to recrystallize and activate amorphized germanium doped with phosphorous by ion implantation. The structural modifications induced during the recrystallization and the related dopant diffusion were first investigated. After LTA at low energy densities, the P electrical activation was poor while the dopant distribution was mainly localized in the polycrystalline Ge resulting from the anneal. Conversely, full dopant activation (up to 1 × 10 cm) in a perfectly recrystallized material was observed after annealing at higher energy densities. Measurements of lattice parameters performed on the fully activated structures show that P doping results in a lattice expansion, with a perpendicular lattice strain per atom ? = +0.7 ± 0.1 Å. This clearly indicates that, despite the small atomic radius of P compared to Ge, the "electronic contribution" to the lattice parameter modification (due to the increased hydrostatic deformation potential in the conduction band of P doped Ge) is larger than the "size mismatch contribution" associated with the atomic radii. Such behavior, predicted by theory, is observed experimentally for the first time, thanks to the high sensitivity of the measurement techniques used in this work.

Co-doping with fluorine is a potentially promising method for defect passivation to increase the donor electrical activation in highly doped n-type germanium. However, regular high dose donor-fluorine co-implants, followed by conventional thermal treatment of the germanium, typically result in a dramatic loss of the fluorine, as a result of the extremely large diffusivity at elevated temperatures, partly mediated by the solid phase epitaxial regrowth. To circumvent this problem, we propose and experimentally demonstrate two non-amorphizing co-implantation methods; one involving consecutive, low dose fluorine implants, intertwined with rapid thermal annealing and the second, involving heating of the target wafer during implantation. Our study confirms that the fluorine solubility in germanium is defect-mediated and we reveal the extent to which both of these strategies can be effective in retaining large fractions of both the implanted fluorine and, critically, phosphorus donors. Published by AIP Publishing.

A systematic study of the indiffusion of oxygen in germanium induced by pulsed laser melting (PLM) is reported. In order to evidence the impact of the experimental parameters, different processing conditions have been compared, i.e. with or without pre-PLM etching of the Ge native oxide by H2O or HF dip, Air or N-2-rich atmosphere, and single or multi-pulse PLM. Oxygen indiffusion is always observed with surface concentration above 1 x 10(19) cm(-3 )for all the processing conditions. Pre-PLM surface chemical treatments seem to have no significant influence in terms of the oxygen penetration, although HF allows lower surface roughening. On the contrary, a processing atmosphere with reduced oxygen concentration is more efficient in reducing the overall O indiffusion. The present experimental results are crucial in view of the implementation of the PLM technique for highly doped Ge as well as to design studies where contamination issue might be crucial.

Obtaining high level active n(+) carrier concentrations in germanium (Ge) has been a significant challenge for further development of Ge devices. By ion implanting phosphorus (P) and fluorine (F) into Ge and restoring crystallinity using Nd: YAG nanosecond pulsed laser melting (PLM), we demonstrate 10(20) cm(-3) n(+) carrier concentration in tensile-strained epitaxial germanium-on-silicon. Scanning electron microscopy shows that after laser treatment, samples implanted with P have an ablated surface, whereas P+F co-implanted samples have good crystallinity and a smooth surface topography. We characterize P and F concentration depth profiles using secondary ion mass spectrometry and spreading resistance profiling. The peak carrier concentration, 10(20) cm(-3) at 80 nm below the surface, coincides with the peak F concentration, illustrating the key role of F in increasing donor activation. Cross-sectional transmission electron microscopy of the co-implanted sample shows that the Ge epilayer region damaged during implantation is a single crystal after PLM. High-resolution X-ray diffraction and Raman spectroscopy measurements both indicate that the as-grown epitaxial layer strain is preserved after PLM. These results demonstrate that co-implantation and PLM can achieve the combination of n(+) carrier concentration and strain in Ge epilayers necessary for next-generation, high-performance Ge-on-Si devices. Published by AIP Publishing.

Due to their interesting optical and electronic properties, silicon nanocrystals (Si NCs) are the subject of intense research activity. The definition of their electronic structure is not trivial, neither from a theoretical nor from an experimental point of view. In fact, the models and methodologies developed for bulk materials cannot be directly applied to study these nanostructures where size-related effects, like quantum confinement (QC) and surface related phenomena, play a major role. In this work, X-ray Photoelectron Spectroscopy (XPS) was used to study the electronic structure of Si NCs embedded in SiO2. The energy differences among Si0+ 2s and Si0+ 2p core levels and the valence band maximum (VBM) were monitored. XPS data were combined with a direct measurement of the energy band gap by photoluminescence analysis, providing a complete picture of the electronic structure of Si NCs as a function of their size. Experimental data indicate a progressive reduction of energy differences among core levels and the VBM when decreasing the average diameter of the Si NCs. No concomitant shift of the conduction band minimum (CBM) was observed. The electronic structure of P-doped Si NCs was investigated as well, showing a concurrent shift of the VBM and the CBM as a function of P concentration.

The functionalization and subsequent monolayer doping of In GaAs substrates using a tin-containing molecule and a compound containing both silicon and sulfur was investigated. Epitaxial InGaAs layers were grown on semi-insulating InP wafers and functionalized with both sulfur and silicon using mercaptopropyltriethoxysilane and with tin using allyltributylstannane. The functionalized surfaces were characterized using X-ray photoelectron spectroscopy (XPS). The surfaces were capped and subjected to rapid thermal annealing to cause in-diffusion of dopant atoms. Dopant diffusion was monitored using secondary ion mass spectrometry. Raman scattering was utilized to nondestructively determine the presence of dopant atoms, prior to destructive analysis, by comparison to a blank undoped sample. Additionally, due to the Asdominant surface chemistry, the resistance of the functionalized surfaces to oxidation in ambient conditions over periods of 24 h and 1 week was elucidated using XPS by monitoring the As 3d core level for the presence of oxide components.

Laser annealing of semiconductor materials is a processing technique offering interesting application features when intense, transient and localized heat sources are needed for electronic device manufacturing or other nano-technological applications. The space-time localization of the induced thermal field (in the nanoseconds/nanometers scale) promotes interesting non-equilibrium phenomena in the processed material which only recently have been systematically investigated and modelled. In this review paper we discuss the current knowledge on anomalous kinetics occurring in implanted silicon and germanium (i.e. thin layers of disorder diluted alloys of Si and Ge, with variable initial disorder status according to the implantation conditions) during the pulsed laser irradiation. In particular, we focus our attention on the anomalous impurity redistribution in the transient melting stage and on the formation of non conventional and metastable extended defects.

Heavy doping of Ge is crucial for several advanced micro- and optoelectronic applications, but, at the same time, it still remains extremely challenging. Ge heavily n-type doped at a concentration of 1 × 10cm by As ion implantation and melting laser thermal annealing (LTA) is shown here to be highly metastable. Upon post-LTA conventional thermal annealing As electrically deactivates already at 350 °C reaching an active concentration of ~4 × 10cm. No significant As diffusion is detected up to 450 °C, where the As activation decreases further to ~3 × 10cm. The reason for the observed detrimental deactivation was investigated by Atom Probe Tomography and in situ High Resolution X-Ray Diffraction measurements. In general, the thermal stability of heavily doped Ge layers needs to be carefully evaluated because, as shown here, deactivation might occur at very low temperatures, close to those required for low resistivity Ohmic contacting of n-type Ge.

High n-type doping in germanium is essential for many electronic and optoelectronic applications especially for high performance Ohmic contacts, lasing and mid-infrared plasmonics. We report on the combination of in situ doping and excimer laser annealing to improve the activation of phosphorous in germanium. An activated n-doping concentration of 8.8 x 10(19) cm(-3) has been achieved starting from an incorporated phosphorous concentration of 1.1 x 10(20) cm(-3). Infrared reflectivity data fitted with a multi-layer Drude model indicate good uniformity over a 350 nm thick layer. Photoluminescence demonstrates clear bandgap narrowing and an increased ratio of direct to indirect bandgap emission confirming the high doping densities achieved.

Highly n-type Ge attained by shallow As implantation and excimer laser annealing was studied with positron annihilation spectroscopy and theoretical calculations. We conclude that a high concentration of vacancy-arsenic complexes was introduced by the doping method, while no sign of vacancies was seen in the un-implanted laser-annealed samples. The arsenic bound to the complexes contributes substantially to the passivation of the dopants. Published by AIP Publishing.

The microscopic mechanisms involving dopants, contaminants, and defects in Ge during pulsed melting laser thermal annealing (LTA) are investigated in detail. Samples both un-implanted and implanted with As or B are processed by LTA as well as characterized in terms of chemical (1D and 3D), electrical, and strain profiling. The clustering of As is directly measured by 3D chemical profiling and correlated with its partial electrical activation along with a reduction of the lattice strain induced by As atoms. A semi-quantitative microscopic model involving the interaction with mobile As-vacancy (AsV) complexes is proposed to describe the clustering mechanism. Boron is shown to follow different clustering behavior that changes with depth and marked by completely different strain levels. Oxygen penetrates from the surface into all the samples as a result of LTA and, only in un-implanted Ge, it occupies an interstitial position inducing also positive strain in the lattice. On the contrary, data suggest that the presence of As or B forces O to assume different configurations with negligible strain, through O-V or O-B interactions for the two dopant species, respectively. These data suggest that LTA does not inject a significant amount of vacancies in Ge, at variance with Si, unless As atoms or possibly other n-type dopants are present. These results have to be carefully considered for modeling the LTA process in Ge and its implementation in technology. (C) 2016 AIP Publishing LLC.

Heavily doped semiconductor thin films are very promising for application in mid-infrared plasmonic devices because the real part of their dielectric function is negative and broadly tunable in the 5 to 50?m wavelength range at least. In this work, we investigate the electrodynamics of heavily n-type-doped germanium epilayers at infrared frequencies beyond the assumptions of the Drude model. The films are grown on silicon and germanium substrates, are in situ doped with phosphorous in the 1017 to 1019 cm-3 range, then screened plasma frequencies in the 100 to 1200cm-1 range were observed. We employ infrared spectroscopy, pump-probe spectroscopy, and dc transport measurements to determine the tunability of the plasma frequency. Although no plasmonic structures have been realized in this work, we derive estimates of the decay time of mid-infrared plasmons and of their figures of merit for field confinement and for surface plasmon propagation. The average electron scattering rate increases almost linearly with excitation frequency, in agreement with quantum calculations based on a model of the ellipsoidal Fermi surface at the conduction band minimum of germanium accounting for electron scattering with optical phonons and charged impurities. Instead, we found weak dependence of plasmon losses on neutral impurity density. In films where a transient plasma was generated by optical pumping, we found significant dependence of the energy relaxation times in the few-picosecond range on the static doping level of the film, confirming the key but indirect role played by charged impurities in energy relaxation. Our results indicate that underdamped mid-infrared plasma oscillations are attained in n-type-doped germanium at room temperature.

Achieving the required control of dopant distribution and selectivity for nanostructured semiconducting building block is a key issue for a large variety of applications. A promising strategy is monolayer doping (MLD), which consists in the creation of a well-ordered monolayer of dopant-containing molecules bonded to the surface of the substrate. In this work, we synthesize a P delta-layer embedded in a SiO2 matrix by MLD. Using a multi-technique approach based on time of flight secondary ion mass spectrometry (ToF-SIMS) and Rutherford backscattering spectrometry (RBS) analyses, we characterize the tuning of P dose as a function of the processing time and temperature. We found the proper conditions for a full grafting of the molecules, reaching a maximal dose of 8.3 x 10(14) atoms/cm(2). Moreover, using 1D rate equation model, we model P diffusion in SiO2 after annealing and we extract a P diffusivity in SiO2 of 1.5 x 10(17) cm(2) s(-1).

Over the past decades, information technology had an enormous and a continuously increasing impact in our daily life and society. This has been made possible by the aggressive scaling of the metal oxide semiconductor field effect transistors (MOSFETs), i.e., the building block of microelectronic (and, now, nanoelectronic) integrated circuits, following the well known Moore's law (ITRS, 2013). The driving force for the continuous huge research efforts to maintain this trend over the years has been the performance and the economic outcomes deriving from device miniaturization.

Third-generation TiO photocatalysts were prepared by implantation of C ions into 110nm thick TiO films. An accurate structural investigation was performed by Rutherford backscattering spectrometry, secondary ion mass spectrometry, X-ray diffraction, Raman-luminescence spectroscopy, and UV/VIS optical characterization. The C doping locally modified the TiO pure films, lowering the band-gap energy from 3.3eV to a value of 1.8eV, making the material sensitive to visible light. The synthesized materials are photocatalytically active in the degradation of organic compounds in water under both UV and visible light irradiation, without the help of any additional thermal treatment. These results increase the understanding of the C-doped titanium dioxide, helpful for future environmental applications.

In this work we focus on P doping of Si nanocrystals (NCs) embedded in a SiO2 matrix. We prove that, at equilibrium, high P concentrations within the Si NCs are thermodynamically favoured. We experimentally estimate the energy barriers for P diffusion in SiO2 and trapping/de-trapping at the SiO2/Si NCs interface, obtaining a complete picture of the system at equilibrium.