On the insulator-to-metal transition in titanium-implanted silicon

Hyperdoped silicon with deep level impurities has attracted much research interest due to its promising optical and electrical properties. In this work, single crystalline silicon supersaturated with titanium is fabricated by ion implantation followed by both pulsed laser melting and flash lamp annealing. The decrease of sheet resistance with increasing Ti concentration is attributed to a surface morphology effect due to the formation of cellular breakdown at the surface and the percolation conduction at high Ti concentration is responsible for the metallic-like conductivity. The insulator-to-metal transition does not happen. However, the doping effect of Ti incorporation at low concentration is not excluded, which might be responsible for the sub-bandgap optical absorption reported in literature.

Room-temperature short-wavelength infrared Si photodetector

The optoelectronic applications of Si are restricted to the visible and near-infrared spectral range due to its 1.12 eV-indirect band gap. Sub-band gap light detection in Si, for instance, has been a long-standing scientific challenge for many decades since most photons with sub-band gap energies pass through Si unabsorbed. This fundamental shortcoming, however, can be overcome by introducing non-equilibrium deep-level dopant concentrations into Si, which results in the formation of an impurity band allowing for strong sub-band gap absorption. Here, we present steady-state room-temperature short-wavelength infrared p-n photodiodes from single-crystalline Si hyperdoped with Se concentrations as high as 9 × 10²⁰ cm⁻³, which are introduced by a robust and reliable non-equilibrium processing consisting of ion implantation followed by millisecond-range flash lamp annealing. We provide a detailed description of the material properties, working principle and performance of the photodiodes as well as the main features in the studied wavelength region. This work fundamentally contributes to establish the short-wavelength infrared detection by hyperdoped Si in the forefront of the state-of-the-art of short-IR Si photonics.

Ultra-doped n-type germanium thin films for sensing in the mid-infrared

A key milestone for the next generation of high-performance multifunctional microelectronic devices is the monolithic integration of high-mobility materials with Si technology. The use of Ge instead of Si as a basic material in nanoelectronics would need homogeneous p- and n-type doping with high carrier densities. Here we use ion implantation followed by rear side flash-lamp annealing (r-FLA) for the fabrication of heavily doped n-type Ge with high mobility. This approach, in contrast to conventional annealing procedures, leads to the full recrystallization of Ge films and high P activation. In this way single crystalline Ge thin films free of defects with maximum attained carrier concentrations of 2.20 ± 0.11 × 10(20) cm(-3) and carrier mobilities above 260 cm(2)/(V·s) were obtained. The obtained ultra-doped Ge films display a room-temperature plasma frequency above 1,850 cm(-1), which enables to exploit the plasmonic properties of Ge for sensing in the mid-infrared spectral range.

Synthesis, Morphological, and Electro-optical Characterizations of Metal/Semiconductor Nanowire Heterostructures

In this letter, we demonstrate the formation of unique Ga/GaAs/Si nanowire heterostructures, which were successfully implemented in nanoscale light-emitting devices with visible room temperature electroluminescence. Based on our recent approach for the integration of InAs/Si heterostructures into Si nanowires by ion implantation and flash lamp annealing, we developed a routine that has proven to be suitable for the monolithic integration of GaAs nanocrystallite segments into the core of silicon nanowires. The formation of a Ga segment adjacent to longer GaAs nanocrystallites resulted in Schottky-diode-like I/V characteristics with distinct electroluminescence originating from the GaAs nanocrystallite for the nanowire device operated in the reverse breakdown regime. The observed electroluminescence was ascribed to radiative band-to-band recombinations resulting in distinct emission peaks and a low contribution due to intraband transition, which were also observed under forward bias. Simulations of the obtained nanowire heterostructure confirmed the proposed impact ionization process responsible for hot carrier luminescence. This approach may enable a new route for on-chip photonic devices used for light emission or detection purposes.

Hyperdoping silicon with selenium: solid vs. liquid phase epitaxy

Chalcogen-hyperdoped silicon shows potential applications in silicon-based infrared photodetectors and intermediate band solar cells. Due to the low solid solubility limits of chalcogen elements in silicon, these materials were previously realized by femtosecond or nanosecond laser annealing of implanted silicon or bare silicon in certain background gases. The high energy density deposited on the silicon surface leads to a liquid phase and the fast recrystallization velocity allows trapping of chalcogen into the silicon matrix. However, this method encounters the problem of surface segregation. In this paper, we propose a solid phase processing by flash-lamp annealing in the millisecond range, which is in between the conventional rapid thermal annealing and pulsed laser annealing. Flash lamp annealed selenium-implanted silicon shows a substitutional fraction of ~ 70% with an implanted concentration up to 2.3%. The resistivity is lower and the carrier mobility is higher than those of nanosecond pulsed laser annealed samples. Our results show that flash-lamp annealing is superior to laser annealing in preventing surface segregation and in allowing scalability.

InP nanocrystals on silicon for optoelectronic applications

One of the solutions enabling performance progress, which can overcome the downsizing limit in silicon technology, is the integration of different functional optoelectronic devices within a single chip. Silicon with its indirect band gap has poor optical properties, which is its main drawback. Therefore, a different material has to be used for the on-chip optical interconnections, e.g. a direct band gap III-V compound semiconductor material. In the paper we present the synthesis of single crystalline InP nanodots (NDs) on silicon using combined ion implantation and millisecond flash lamp annealing techniques. The optical and microstructural investigations reveal the growth of high-quality (100)-oriented InP nanocrystals. The current-voltage measurements confirm the formation of an n-p heterojunction between the InP NDs and silicon. The main advantage of our method is its integration with large-scale silicon technology, which allows applying it for Si-based optoelectronic devices.

Ion Implantation and Annealing Effects in Silicon Carbide

SiC is a promising semiconductor material for high-power/high-frequency and hightemperature electronic applications. For selective doping of SiC ion implantation is the only possible process. However, relatively little is known about ion implantation and annealing effects in SiC. Compared to ion implantation into Si there is a number of specific features which have to be considered for successful ion beam processing of SiC. A brief review is given on some aspects of ion implantation in and annealing of SiC. The ion implantation effects in SiC are discussed in direct comparison to Si. The following issues are addressed: ion ranges, radiation damage, amorphization, high temperature implantation, ion beim induced crystallization and surface erosion.

n-InAs nanopyramids fully integrated into silicon

InAs with an extremely high electron mobility (up to 40,000 cm(2)/V s) seems to be the most suitable candidate for better electronic devices performance. Here we present a synthesis of inverted crystalline InAs nanopyramids (NPs) in silicon using a combined hot ion implantation and millisecond flash lamp annealing techniques. Conventional selective etching was used to form the InAs/Si heterojunction. The current-voltage measurement confirms the heterojunction diode formation with the ideality factor of η = 4.6. Kelvin probe force microscopy measurements indicate a type-II band alignment of n-type InAs NPs on p-type silicon. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based electronic devices.

Advanced Thermal Processing of Semiconductor Materials by Flash Lamp Annealing

The use of flash lamp annealing for processing semiconductor materials is outlined. Specific applications include ultra-shallow junction formation and heteroepitaxial growth of improved quality thin films of cubic silicon carbide. It is demonstrated that flash lamp annealing holds great promise as a technique for fabricating novel devices.

Amortization and Recrystallization of 6H-SiC by ion Beam Irradiation

The evolution of the damage in the near surface region of single crystalline 6H-SiC generated by 200 keV Ge+ ion implantation at room temperature (RT) was investigated by Rutherford backscattering spectroscopy/chanelling (RBS/C). The threshold dose for amorphization was found to be about 3 · 1014 cm-2, Amorphous surface layers produced with Ge+ ion doses above the threshold were partly annealed by 300 keV Si+ ion beam induced epitaxial crystallization (IBIEC) at a relatively low temperature of 480°C For comparison, temperatures of at least 1450°C are necessary to recrystallize amorphous SiC layers without assisting ion irradiation. The structure and quality of both the amorphous and recrystallized layers were characterized by cross-section transmission electron microscopy (XTEM). Density changes of SiC due to amorphization were measured by step height measurements.

Helium Induced Cavities in Silicon: Their Formation, Microstructure and Gettering Ability

The formation of cavity microstructures in silicon following helium implantation (10 or 40 keV; 1×1015, l×1016 and 5×1016 cm−2) and annealing (800 °C) is investigated by means of Transmission Electron Microscopy (TEM), Rutherford Backscattering Spectrometry and Channeling (RBS/C), and Elastic Recoil Detection (ERD). The processes of cavity nucleation and growth are found to depend critically on the implanted He concentration. For a maximum peak He concentration of about 5×1020 cm−3 the resulting microstructure appears to contain large overpressurized bubbles whose formation cannot be accounted by the conventional gas-release model and bubble-coarsening mechanisms predicting empty cavities. The trapping of Fe and Cu at such cavity regions is studied by Secondary Ion Mass Spectrometry (SIMS).

Ion Beam Induced Epitaxial Crystallization of Single Crystalline 6H-SiC

For the first time, ion beam induced epitaxial crystallization (IBIEC) has been found in SiC. The effect of 300 keV Si+ irradiation through an amorphous surface layer in single crystalline 6H-SiC at 477+5°C has been investigated by RBS/C and XTEM. A shrinkage of the amorphous layer was found after ion irradiation at this temperature which is caused by both an ion dose independent thermal regrowth of about 20 nm and an additional ion beam induced epitaxial crystallization with a rate of about 1.5 nm/ 1016 cm−2.

Carrier profiling of individual Si nanowires by scanning spreading resistance microscopy

Individual silicon nanowires (NWs) doped either by ion implantation or by in situ dopant incorporation during NW growth were investigated by scanning spreading resistance microscopy (SSRM). The carrier profiles across the axial cross sections of the NWs are derived from the measured spreading resistance values and calibrated by the known carrier concentrations of the connected Si substrate or epi-layer. In the case of the phosphorus ion-implanted and subsequently annealed NWs, the SSRM profiles revealed a radial core-shell distribution of the activated dopants. The carrier concentration close to the surface of a phosphorus-doped NW is found to be by a factor of 6-7 higher than the value in the core and on average only 25% of the implanted phosphorus is electrically active. In contrast, for the in situ boron-doped NW the activation rate of the boron atoms is significantly higher than for phosphorus atoms. Some specific features of SSRM experiments of Si NWs are discussed including the possibility of three-dimensional measurements.

A Novel Method to Fabricate Silicon Nanowire p-n Junctions by a Combination of Ion Implantation and in-situ Doping

We demonstrate a novel method to fabricate an axial p-n junction inside <111> oriented short vertical silicon nanowires grown by molecular beam epitaxy by combining ion implantation with in-situ doping. The lower halves of the nanowires were doped in-situ with boron (concentration ~1018cm-3), while the upper halves were doubly implanted with phosphorus to yield a uniform concentration of 2 × 1019 cm-3. Electrical measurements of individually contacted nanowires showed excellent diode characteristics and ideality factors close to 2. We think that this value of ideality factors arises out of a high rate of carrier recombination through surface states in the native oxide covering the nanowires.

Superconducting state in a gallium-doped germanium layer at low temperatures

We demonstrate that the third elemental group-IV semiconductor, germanium, exhibits superconductivity at ambient pressure. Using advanced doping and annealing techniques of state-of-the-art semiconductor processing, we have fabricated a highly Ga-doped Ge (GeratioGa) layer in near-intrinsic Ge. Depending on the detailed annealing conditions, we demonstrate that superconductivity can be generated and tailored in the doped semiconducting Ge host at temperatures as high as 0.5 K. Critical-field measurements reveal the quasi-two-dimensional character of superconductivity in the approximately 60 nm thick GeratioGa layer. The Cooper-pair density in GeratioGa appears to be exceptionally low.

[Use of methotrexate for treatment of corticosteroid-dependent asthma]

We evaluated the effects of methotrexate treatment in 20 subjects (10 men, 10 women) suffering from corticosteroid-dependent asthma. All patients had been treated with 15 mg of prednisone or more per day for at least 3 years before including in the study. Methotrexate (15 mg once weekly) had been given for 9.7 months on average. Oral steroid intake was reduced by 50% in 8 patients and it was possible to discontinue oral corticosteroids in further 6 patients without deterioration of spirometric parameters at the end of the study. Side effects of methotrexate therapy were observed in 40% of patients, and required the discontinuation of treatment in 6 subjects.

[Cystic fibrosis in adults--clinical aspects]

Nineteen patients with cystic fibrosis were seen in the I Department of Tuberculosis and Lung Diseases during 3.5 years. There were 12 (63%) female, and 7 male, aged from 16 to 35 years (mean 23.2). Most patients were diagnosed in childhood, but 4 were diagnosed in their early adulthood. The diagnosis was confirmed by positive chloride sweat test in all cases. Molecular DNA analyses were performed in 16 cases. In 9 (56%) cases two mutations in the CFTR gene were identified. In 5 cases one mutation was identified. All patients had bronchiectases confirmed by CT. Spirometry showed lung function impairment with predominantly obstructive pattern. Mean VC was 2.57l, mean FEVI was 1.66l. In 7 (37%) cases FEVI was lower then 30% of predictive value. Hypoxemia was found in 11 (58%) cases and hypercapnia in 3 (16%) cases. Sputum cultures were positive for mucoid P. aeruginosa in 12 (63%) cases, for Staph. aureus in 16 (84%) cases. Persistent colonisation with nontuberculous mycobacteria was found in 2 (10.5%) cases. Aspergillus fumigatus was identified in sputum cultures in 2 subjects who had also positive precipitation test. Diabetes mellitus was diagnosed in 2 cases. Meconium ileus equivalent was seen in 1 case. Pneumothorax was seen in 1 case. One patient died in the endstage of the illness.

[Deaths from asthma, bronchitis and pulmonary heart disease in Warsaw in the years 1993-1994]

By the regular checking the death certificates in the municipal offices in 7 districts of Warsaw, the morality rate from asthma has been established as 2.98/100.000, from chronic bronchitis as 8.71/100.000 and from pulmonary heart disease as 6.27/100.000. During one year of this survey only 15 deaths (4.7%) from these diseases were below age of 50.67% of patients died in hospitals and 22 (7%) died suddenly (at home). In general, deaths reported as the results of COLD were only 1.59% of the total number of deaths in Warsaw (21.530). 6.9% of all death certificates were without clinical diagnosis (Number 798 of ICD)-described as "natural death", "death before doctor's arrival" or "noncriminal death". Authors discuss the problem of over- and under-diagnosis of asthma as the cause of death, the historical background of asthma mortality and also put the question of the righteousness of regard the pulmonary heart disease as the primary cause of death.