Shallow Sb-doped Si surface layers formed by recoil implantation

Recoil implantation was used to form shallow n+ layers on p-Si by implanting 150 keV Ar⁺ ions through evaporated Sb layers. By varying the Sb layer thickness, different dopant profiles were achieved. Based on the sheet resistance measurements, it was found that the dopant profiles deviated from theory when the Sb layer thickness was small. Damage effects related to energy deposition by the primary ions were used to explain the differences. It was suggested that these effects could significantly affect the dopant activity and the redistribution of the atoms during heat treatment. These effects were less important for those samples with thick Sb layers. For shallow p-n junction formation, it was essential to keep the damage effects to a low level.     

Surface hardness improvement by dynamic recoil implantation

Substantial increase of mild steel hardness is achieved by a novel recoil implantation technique. The technique is described and the results are analysed in view of the effects of radiation damage and the implant's concentration profile.     

Graphene synthesis by cold implantation of carbon recoil atoms

A new method of introducing carbon into catalytic metal films for graphene synthesis is proposed. The method is based on the phenomenon of carbon recoil atoms from a layer of methane molecules that are adsorbed on a metal film being incorporated into this film under the action of bombardment with inert gas ions. To increase the thickness of adsorbed methane layer, the substrate is cooled down to ?190°C. The proposed method has been implemented on a polycrystalline nickel film. After the final annealing, Raman spectroscopy showed the presence of numerous fragments of multilayer graphene on the film surface.     

Study of ultra-shallow pn junctions formed by excimer laser annealing

Excellent ultra-shallow p⁺n junctions have been formed by thermally treating the BF₂⁺-implanted Si samples by excimer laser annealing (ELA) at 300–400 mJ cm⁻² with post low-temperature long-time furnace annealing (FA) at 600 °C. A junction with a leakage current density lower than 20 nA cm⁻² and a sheet resistance smaller than 200 Ω □⁻¹ can be well achieved. No considerable dopant diffusion is observed by using this low-thermal-budget annealing process. However, by simply using the ELA treatment at 300–400 mJ cm⁻², the resultant junction shows a leakage current density as high as 10⁴ nA cm⁻² and a peripheral leakage current density of 10³ nA cm⁻¹. The large junction leakage is primarily due to the leakage current generated within the junction region near the local-oxidation-of-silicon (LOCOS) edge, and which is substantially caused by the ELA treatment. The large peripheral junction leakage current density can be significantly reduced to be about 0.2 nA cm⁻¹ after a post low-temperature FA treatment at 600 °C. As a result, the scheme that employs ELA treatment with post low-temperature FA treatment would be efficient for forming excellent ultra-shallow p⁺n junctions at low thermal budget.     

Rectifying pyronine-B/p-type silicon junctions formed by sublimation of pyronine-B

The rectifying junction characteristics of the organic compound pyronine-B film on a p-type Si substrate have been studied. The pyronine-B has been sublimed onto the top of p-Si surface. The barrier height and ideality factor values of 0.79 eV and 1.125 for this structure have been obtained from the forward-bias current–voltage characteristics. The density distribution of the interface states in the inorganic semiconductor bandgap and their relaxation time have been determined from the low-capacitance–frequency characteristics by the Schottky capacitance spectroscopy method. The measurement frequency varies from 90 Hz to 10 MHz. The interface state density N_ss ranges from 2.10×10¹⁰ cm^–2 eV^–1 in (0.79–E_v) eV to 1.16×10¹² cm^–2 eV^–1 in (0.53–E_v) eV. Furthermore, the relaxation time ranges from 1.38×10^–3 s in (0.53–F_V) eV to 7.50×10^–3 s in (0.79–E_V) eV.     

Deuterium trapping in iron alloys formed by ion implantation

The main results of several years' work on MIS structures based on germanium are presented. We studied the properties of the interfaces between germanium and germanium dioxide, germanium and silicon dioxide, germanium and silicon nitride and also germanium and double-layer SiO₂Si₃N₄ dielectric films. The main electrophysical characteristics of the various interfaces were compared bearing in mind the techniques of their fabrication. The important role of carriers tunnelling into traps is described. The characteristics of a germanium MIS transistor are discussed and the structural defects of the interfaces and their effect on the electrophysical characteristics of the transistor are briefly considered.     

ZnO nanobelt/nanowire Schottky diodes formed by dielectrophoresis alignment across au electrodes

Rectifying diodes of single nanobelt/nanowire-based devices have been fabricated by aligning single ZnO nanobelts/nanowires across paired Au electrodes using dielectrophoresis. A current of 0.5 microA at 1.5 V forward bias has been received, and the diode can bear an applied voltage of up to 10 V. The ideality factor of the diode is approximately 3, and the on-to-off current ratio is as high as 2,000. The detailed IV characteristics of the Schottky diodes have been investigated at low temperatures. The formation of the Schottky diodes is suggested due to the asymmetric contacts formed in the dielectrophoresis aligning process.     

Imaging Schottky barriers and ohmic contacts in PbS quantum dot devices

We fabricated planar PbS quantum dot devices with ohmic and Schottky type electrodes and characterized them using scanning photocurrent and photovoltage microscopies. The microscopy techniques used in this investigation allow for interrogation of the lateral depletion width and related photovoltaic properties in the planar Schottky type contacts. Titanium/QD contacts exhibited depletion widths that varied over a wide range as a function of bias voltage, while the gold/QD contacts showed ohmic behavior over the same voltage range.     

Radial junctions formed by conformal chemical doping for innovative hole-based solar cells

In this paper an innovative approach for Si solar cells based on radial junctions is presented. It consists of fabricating the junction in quasi one-dimensional structures like holes. The hole-based architecture, while maintaining the decoupling between the light absorption and the electrical collection typical of the more common wires and rods, ensures more robustness, numerous waveguide coupling modes and possibility to form non-conformal top contact. Nanosizes also provide the possibility to tune the band gap by quantum effects. Doping of the nanoholes, like in the case of nanowires, presents critical issues like conformality and control of the dopant dose and junction depth at nanometric level. We propose to dope the nanoholes by using a chemical method based on the use of a dopant containing molecules dispersed in solution. We apply the procedure on an array of holes of micrometric sizes fabricated to test and study the method and to properly scale it down and implement it on the nanostructures. Results show that the method provides junction depths in the nm scale with dopant peak concentrations as high as 10¹⁹ cm^?3 and that the doping is conformal on the vertical surfaces of the hole.     

Imaging of the Schottky barriers and charge depletion in carbon nanotube transistors

The photovoltage produced by local illumination at the Schottky contacts of carbon nanotube field-effect transistors varies substantially with gate voltage. This is particularly pronounced in ambipolar nanotube transistors where the photovoltage switches sign as the device changes from p-type to n-type. The detailed transition through the insulating state can be recorded by mapping the open-circuit photovoltage as a function of excitation position. These photovoltage images show that the band-bending length can grow to many microns when the device is depleted. In our palladium-contacted devices, the Schottky barrier for electrons is much higher than that for holes, explaining the higher p-type current in the transistor. The depletion width is 1.5 mum near the n-type threshold and smaller than our resolution of 400 nm near the p-type threshold. Internal photoemission from the metal contact to the carbon nanotube and thermally assisted tunneling through the Schottky barrier are observed in addition to the photocurrent that is generated inside the carbon nanotube.     

Properties of WN x /GaAs Schottky contacts prepared by ion implantation of nitrogen

The formation of WN _x /GaAs Schottky contacts using selective ion implantation of nitrogen into the sputtered tungsten film has been demonstrated. The contacts were characterized by Auger electron spectroscopy and current-voltage measurements. The composition of WN _x films and the thermal stability of WN _x /GaAs contacts were investigated. Good thermal stability of WN _x /GaAs contacts compared with a W/GaAs contact was observed after capless rapid thermal annealing at 450, 800 and 950°C for 10 s.     

氢氧复合注入对SOI-SIMOX埋层结构影响的研究

实验研究了氢、氧复合注入对注氧隔离技术制备SOI（Silicon On Insulator)材料埋层结构的影响。用截面透射电子显微镜和二次离子质谱技术分析了退火前后材料的微结构变化。研究表明，氢离子的注入有利于注氧隔离制备的SOI材料埋层的增宽。进一步的结果表明，室温氢离子注入导致的增宽效应比高温注入明显。     

Electric stability of spatiotemporal stripe patterns formed by silver and antimony co-electrodeposition under the constant current mode

During Ag/Sb (silver and antimony) co-electrodeposition, various spatiotemporal patterns, which are similar to those in the reaction–diffusion system, are observed on the metal electrode surface. In our previous paper, we reported the phase diagram of several kinds of propagating stripe patterns as a function of constant current density, using an optical microscope. For several phases in the phase diagram, we discovered that the spatial bifurcation to two dynamic stripe patterns took place on the electrode surface at the initial stage of electrodeposition, and eventually, these two patterns transferred into one of the patterns in time. In this study, in order to compare the electric stability of such patterns, the potential time-evolution of each phase, in which the spatial bifurcation of patterns occurs, was investigated. From the experimental results, it was found that the patterns each have an inherent range or value of potential at which they are formed. However, the potential did not necessarily reach the value with low electric energy. Namely, this finding indicates that various other factors contribute to this phenomenon in addition to the electric stability.     

Dimensions of the crater formed by the penetration of fast particles into solid barriers

Semiempirical relations are presented for determining the depth and diameter of the crater formed by 16 km/sec spherical particles penetrating into a solid semiinfinite barrier.     

Improvement of Ta-based thin film barriers on copper by ion implantation of nitrogen and oxygen

Magnetron sputtered polycrystalline Ta and Ta(Si) barriers for copper metallization schemes were modified by nitrogen as well as oxygen high dose ion implantation to improve their thermo-mechanical stability. Ion bombardment changed the initial polycrystalline microstructure to amorphous-like. In contrast to pure Ta, Ta(Si) layers were already amorphous or nanocrystalline after deposition. In this case, the annealing temperature at which formation of a well crystallized structure occurs increased by approximately 100 K as a result of the implantation. In order to demonstrate the improvement in the barrier properties of the implanted Ta films, the intermixing of Ta and Cu at the interface of corresponding layer structures was measured as a function of the annealing temperature by depth profiling using Auger electron spectroscopy (AES). The thermal stability of Ta and Ta(Si) barriers increased from 600 °C/1 h for the non-implanted layers up to 750 °C/1 h after implantation of nitrogen or oxygen.     

Rutherford backscattering analysis of oxide layers formed by ion implantation into single-crystal silicon

Single-crystal silicon was implanted with 40 keV and 60 keV oxygen ions. Rutherford backscattering (RBS) analysis was used to determine the oxygen profile, the ratio of oxygen to silicon in the implanted layer and the extent of radiation damage for doses up to 3 × 10¹⁸ ions cm^-2. The measured oxygen profiles appear to agree with theory at low doses. The radiation damage, as characterized by the damage peak and the yield _χmin behind the implanted layer, saturates at a dose of approximately 1 × 10¹⁶ ions cm^-2. The oxygen content of the layer is directly proportional to dose until the peak value of the oxygen:silicon ratio reaches 2.0. At higher doses the oxygen concentration only increases in the region between the peak and the surface, resulting in a uniform layer of thickness 2R_p (SiO₂). Infrared transmission measurements also indicate that stoichiometric SiO₂ is formed. Annealing at 900 °C has no effect on the RBS spectrum from the implanted layer but the area of the interfacial damage peak is reduced by 60%. Two interesting effects occur: (a) _χmin rises to a peak when the oxygen:silicon ratio is approximately unity; (b) the interfacial damage peak decreases with increasing dose once a uniform layer has been formed.     

Optical effects of doped top layers in silicon-on-insulator structures formed by ion implantation

Arsenic ions were implanted into silicon-on-insulator (SOI) structures at an incident energy of 100 keV to a dose of 2 × 10¹⁵ cm^–2. Conductive top layers were formed in the SOI structures after annealing at 1200 °C for 20 s. Infrared reflection spectra in the wave number range of 1500–5000 cm^–1 were measured and interference fringes, related to free-carrier plasma effects, were observed. By detailed theoretical analysis and computer simulation of infrared reflection spectra, the carrier concentration, the carrier mobility, and the carrier activation efficiency were obtained. The physical interpretation of the results and a critical discussion of the sensitivity of the data, fitted to variation in the parameters, are given.     

Preparation and characterisation of Au/InGaP/GaAs Schottky barriers for radiation damage investigation

High quality Au/InGaP Schottky diodes have been prepared as efficient test structures for a study of the radiation hardness of InGaP as space solar cell material. A detailed characterisation of the metal–semiconductor barriers obtained on both n (free carrier concentration ranging from 3×l0¹⁵ to 1.2×l0¹⁸ cm⁻³) and p-type (3.5×10¹⁷ cm⁻³) InGaP epitaxial layers lattice matched to GaAs substrate has been performed using current–voltage, capacitance–voltage and internal photoemission techniques. Excellent electrical properties were found for low doped (ideality factor of 1.05–1.06, rectification ratio of about 10¹⁰ at 0.7 V, reverse current lower than 1×10⁻¹² A at −2 V) as well as heavily doped samples (rectification ratios of about 10⁵ at 0.6 V). The barrier height values calculated by the different techniques were compared and discussed. Deep level transient spectroscopy (DLTS) spectra obtained on unirradiated samples did not show detectable deep levels with the exception of the heaviest doped sample showing a weak peak associated to the DX centre. After electron irradiation at 9 MeV with doses ranging from 5×l0¹³ to 1.5×10¹⁵ e cm⁻² the samples exhibited a broad dominant peak (activation energy in the 0.90–0.93 eV range) whose intensity increased linearly with the absorbed dose. The broadening of the peak and the observed increase of the corresponding trap concentration with the doping level suggest that this peak could be associated to complexes due to the interaction of primary defects, created by high irradiation energy, with each others and with the shallow impurities.