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The acronym IBIC (Ion Beam Induced Charge) was coined in early 1990's to indicate a scanning microscopy technique which uses MeV ion beams as probes to image the basic electronic properties of semiconductor materials and devices. Since then, IBIC has become a widespread analytical technique to characterize materials for electronics or for radiation detection, as testified by more than 200 papers published so far in peer-reviewed journals. Its success stems from the valuable information IBIC can provide on charge transport phenomena occurring in finished devices, not easily obtainable by other analytical techniques. However, IBIC analysis requires a robust theoretical background to correctly interpret experimental data. In order to illustrate the importance of using a rigorous mathematical formalism, we present in this paper a benchmark IBIC experiment aimed to test the validity of the interpretative model based on the Gunn's theorem and to provide an example of the analytical capability of IBIC to characterize semiconductor devices., 22 pages, 7 figures

Diamond surface hydrogenation is generally carried out with atomic hydrogen obtained by either microwave plasma or heated filaments. Both these techniques present some drawbacks, given by some instabilities and containment difficulties in the former case, and by some surface contamination by the elements of the filaments themselves, which must be very close to the substrate, in the latter. Surface hydrogenation can be easily obtained by molecular hydrogen, at substrate temperatures not much different from those used in the above methods, but only via thermal means and without the aforementioned drawbacks. In this paper we describe a systematic study carried out on hydrogenated surfaces obtained at different temperatures, from 700 to 900 °C, and on different diamond materials (natural and HPHT), by exposing different surfaces such as (100), (111) and (110) to molecular hydrogen. The results indicate that values of surface resistivity are comparable to those obtained using hot filaments, particularly at temperatures around 800 °C, and that the activation energy related to the establishment of surface conductivity is relatively low. Surface resistivity, XPS (X-ray Photoelectron Spectroscopy), AFM and µ-FTIR in reflection-transmission mode data indicate that the efficiency of surface hydrogenation with the consequent low values of surface resistivity is quite similar for the three surface orientations, but also that in the case of (100) orientation this efficiency is lower.

The control of the carrier lifetime profile in semiconductor power devices is of fundamental importance to optimize device parameters. With respect to traditional technologies such as diffusion of metallic impurities, light ion irradiation at low doses provides precise spatial localization of defects acting as carrier traps and recombination centres. Hence, the generation of suitable lifetime profiles obtained by controlling ion fluence and energy allows the reduction of turn-off times and switching losses in power electronic devices. In order to characterise the effects of ion irradiation on carrier lifetime profiles, we have used the ion beam induced charge collection (IBIC) technique in lateral geometry to measure charge collection efficiency (CCE) profiles in silicon p+/n/n+ diodes under different applied bias conditions before and after a frontal 6.5 MeV He++ ion implantation at a total fluence of 2 × 10 12 ions/cm 2 . After the irradiation, the profile shows a clear drop of charge collection efficiency which occurs at the end of the ion range. The formalism based on Shockley–Ramo–Gunn’s theorem was applied to interpret the CCE profiles in both virgin and irradiated samples and to assess the free carrier lifetime profile modification following the radiation damage.

We report experimental evidence of a substantial reduction of the sheet resistance of a commercially available (110) oriented natural diamond surface after exposure not to atomic but to molecular hydrogen. In a conventional CVD reactor, we have merely exposed the sample to high purity molecular hydrogen fluxes at 800 °C. After exposure to air, the surface conductivity increased several orders of magnitude as measured by a professional collinear four-point probe head with tungsten carbide tips. After annealing at 900 °C in vacuum (P

CVD diamond, as other wide energy gap semiconductors or insulators, is known to present polarization effects when used as a nuclear particle detector, which are due to the building up of an internal space-charge electric field and are responsible for “memory” effects if the polarization is not erased. Polarization effects are larger when the thickness of the sample is longer than the drift length of carriers and give rise to a shortening of the electric field region inside the sample. In this work, IBIC (Ion Beam Induced Charge) measurements with 1 and 2 MeV proton beams have been carried out on a relatively thin CVD diamond sample with the conclusion that no memory or hysteresis effects were present even by switching from one polarity to the opposite one in subsequent measurements. However, it resulted that the values of the charge collection efficiency (cce) did depend on counting rate and the lowering at large counting rates was attributed to a local polarization due to trapping. Finally, in some cases cce turned out to be larger than 1, a result which could be either due to local detrapping or to non-blocking contacts.

The primed state of a detector grade CVD diamond sample has been investigated with respect to light illumination during alpha particles (5.5 MeV) detection. The measurements have been carried out as a function of elapsed time after beta-rays priming both in short term (1 h) and in long term (33 h) conditions. The contribution of holes and electrons to the average charge collection efficiency and to total number of counts above a threshold has been qualitatively separated by selecting bias polarity. The behaviour of electron collection after X-ray priming during blue light or UV illumination is improved while the hole one is worsened, confirming previous data. Linearity of the average collection efficiency for alpha particle is observed only at very low doses and in the hole case. Long term stability of both collection efficiency and of total number of counts is observed both in the primed state for holes and during blue light illumination for electrons.

Charge collection efficiency (CCE) profiles of a semi-insulating (SI) gallium arsenide LEC (Liquid Encapsulated Czochralski) Schottky diode have been investigated by lateral Ion Beam Induced Charge collection (IBIC) technique. A focussed 2.4 MeV proton microbeam was scanned over the cleaved surface of a SI-GaAs diode and the charge collection efficiency was evaluated as a function of the ion beam position at different bias voltages. By fitting the CCE profiles with the equations derived by the Shockley–Ramo–Gunn’s theorem, drift lengths of electrons and holes were obtained. Experimental results are consistent with previous OBIC (Optical Beam Induced Current) and SP (Surface Potential) measurements and confirm the model based on the formation of a Mott barrier due to the enhanced electron capture cross section in high field conditions.

Tracking detectors have become an important ingredient in high-energy physics experiments. In order to survive the harsh detection environment of the large hadron collider (LHC), trackers need to have special properties. They must be radiation hard, provide fast collection of charge, be as thin as possible and remove heat from readout electronics. The unique properties of diamond allow it to fulfill these requirements. In this work we present an investigation of the charge transport and luminescence properties of “detector grade” artificial chemical vapour deposition (CVD) diamond devices developed within the CERN RD42 collaboration, performed by means of X-ray micro-beam induced current collection (XBICC) and X-ray micro-beam induced luminescence (XBIL) techniques. XBICC technique allows quantitative estimates of the transport parameters of the material to be evaluated and mapped with micrometric spatial resolution. In particular, the high resolution and sensitivity of the technique has allowed a quantitative study of the inhomogeneity of the charge transport parameter defined as the product of mobility and lifetime for both electron and holes. XBIL represents a technique complementary to ion beam induced luminescence (IBIL), which has already been used by our group, since X-ray energy loss profile in the material is different from that of MeV ions. X-ray induced luminescence maps have been performed simultaneously with induced photocurrent maps, to correlate charge transport and induced luminescence properties of diamond. Simultaneous XBICC and XBIL maps exhibit features of partial complementarity that have been interpreted on the basis of considerations on radiative and non-radiative recombination processes which compete with charge transport efficiency.

Ion microbeam techniques like ion beam-induced charge collection (IBICC) are very powerful methods in order to investigate and to map the transport properties in different technologically important semiconductors and in particular in materials proposed for nuclear detection. Time-resolved ion beam-induced charge collection (TRIBICC) represents a further improvement with respect to more traditional IBICC, since it can supply not only the charge collection efficiency (and through it data on mobility and trapping time of carriers in drift regions) but also the time behaviours of the charge collection. For long collection times, this means to gather information, also about diffusion lengths and lifetimes of carriers in the diffusion regions, which are always present in undepleted electronic devices, in particular power devices, and which are of paramount importance as inputs for simulation codes. By TRIBICC, in fact, some difficulties could be avoided in analysis of data collected in cases when lifetimes and shaping times of electronic chain are similar, and the sensitivity of the method is worse. In order to suitably analyse TRIBICC data, a theoretical model should be available: in general, Ramo's theorem is used, but its validity in cases when space charge is present is questionable. A more general and powerful method is presented in this work by using Gunn's theorem and a particular formulation of the generation function in order to solve the adjoint of the continuity equation in the time-dependent case. An application of this method to a commercial power device is presented and discussed.

Chemical Vapor Deposited (CVD) polycrystalline diamond has been proposed as a radiation-hard alternative to silicon in the extreme radiation levels occurring close to the interaction region of the Large Hadron Collider. Due to an intense research effort, reliable high-quality polycrystalline CVD diamond detectors, with up to 270 μm charge collection distance and good spatial uniformity, are now available. The most recent progress on the diamond quality, on the development of diamond trackers and on radiation hardness studies are presented and discussed.

A 5.5-keV X-ray microprobe was used at the European Synchrotron Radiation Facility in Grenoble (France) to image the transport properties of a ‘detector grade’ polished CVD diamond sample. Qualitative results concerning the spatial distribution of the X-ray-induced current were obtained with a submicrometer spatial resolution. Particular attention has been paid to the dependence of the photoresponse on bias polarity. Interpretation of the photocurrent maps has been drawn on the basis of previous results obtained using the ion beam-induced charge collection (IBIC) technique. Priming effects and polarisation effects are reported and discussed.

Diamond radiation detectors produced by Chemical Vapour Deposition (CVD) have been extensively studied as nuclear detectors both for the application as tracking detectors in high energy physics experiments and for applications in nuclear industry domain. A meaningful measurement to characterise the performance of such devices is the evaluation of the charge collection distance (CCD), i.e. the mean distance the charge carriers travel before being trapped. It is well known that CCD increases with the absorbed dose (priming or pumping process). The priming of diamond is usually explained by the saturation of active traps in the diamond bulk, which are filled by charge carriers generated by the ionisation. However, such a primed state is metastable, i.e. the exposure to light can de-pumps diamond to its initial state. The analysis of ‘pumping’ and ‘de-pumping’ processes is then useful to explain trapping mechanisms and polarisation effects, which limit the performances of diamond detectors. This paper deals with an investigation of the ‘pumping’ process on detector grade CVD diamond samples exposed to some doses of irradiation (X-rays or beta particles). Photoconductivity measurements carried out during monochromatic illumination as well as optical bleaching spectra of thermoluminescence glow curves highlight the passivation effects of some trap levels due to irradiation. A possible interpretation of these effects is presented and discussed, taking into account charge collection efficiency measurements carried out using Am-241 alpha particles.

Ion beam induced charge technique has been used in order to investigate the charge collection properties of 4H–SiC epitaxial Schottky barrier nuclear detectors. In this work, 2 MeV He ions microbeam about 2 μm spot size scanned the total surface area of the detector in order to obtain maps of the charge collection efficiency (CCE) at different bias voltages. The maps turned out to be very homogeneous, with the conclusion that energy resolution of the detectors is not affected by non-homogeneous broadening due to fluctuations of CCE. Fitting the experimental data obtained for low bias voltages—corresponding to depletion layer widths narrower than He ions range—was possible only by including the contribution of diffusion. By this way, holes diffusion length was determined to be 2 μm.

CVD diamond material was used to build position-sensitive detectors for single-charged particles to be employed in high-intensity physics experiments. To obtain position information, metal contacts shaped as strips or pixels are applied to the detector surface for one- or two-dimensional coordinate measurement. Strip detectors 2×4 cm2 in size with a strip distance of 50 μm were tested. Pixel detectors of various pixel sizes were bump bonded to electronics chips and investigated. A key issue for the use of these sensors in high intensity experiments is the radiation hardness. Several irradiation experiments were carried out with pions, protons and neutrons exceeding a fluence of 1015 particles/cm2. The paper presents an overview of the results obtained with strip and pixel detectors in high-energy test beams and summarises the irradiation studies.

Lateral micro-ion beam induced charge (IBIC) is a powerful method to characterize the electrical behavior of chemical vapor deposition (CVD) diamond thin film and further to evaluate its quality. In the process of IBIC data handling, a new model that the product of mobility and lifetime linearly increases from substrate side to growth side was proposed in order to separately analyze the carriers' contributions to charge collection efficiency. IBIC results shows that CVD diamond was primed by irradiation of 46 Gy proton dose with a 82.4% increase of average collection distance due to the space charge elimination inside the CVD diamond after irradiation. (C) 2001 Elsevier Science Ltd. All rights reserved.

Diamond based pixel detectors are a promising radiation-hard technology for use at the LHC. We present first results on a CMS diamond pixel sensor. With a threshold setting of 2000 electrons, an average pixel efficiency of 78% was obtained for normally incident minimum ionizing particles.

An analysis of the charge collection process induced by focused MeV ion beams in semiconductor devices is presented. It is based on the extended Shockley–Ramo theorem that provides a rigorous mathematical tool for the calculation of the induced charge and current under the assumption of a quasi-steady-state operation of the semiconductor device. A complete description of the theory and underlying assumption is given as well as a simple application of the method aimed to evaluate the main transport properties of fully depleted semiconductors from the analysis of frontal and lateral ion beam induced charge collection (IBICC) measurements.

In this article we present the performance of recent chemical vapour deposition (CVD) diamond micro-strip sensors in beam tests. In addition, we present the first comparison of a CVD diamond micro-strip sensor before and after proton irradiation.

The transport properties of silicon p^+-n-n+ diodes with a junction depth of about 47 micro m have been investigated by means of the lateral IBIC technique. Cross section of the samples have been irradiated by a low intensity 5 MeV proton microbeam and the charge pulses have been recorded as a function of incident proton position. The charge collection efficiency (cce) profiles show broad plateau with values close to 100%. The region where the electric field is absent shows exponentially decreasing cce profiles. The estimate of the decay rate allows the diffusion length of the minority carriers in the bulk of the device to be measured. The analytical method presented in this paper takes into account the dependence of the signal rise time on the incident proton position. The entire cce profile is in full agreement with the IBIC theory based on the extended Ramo's theorem, which provides a very effective tool for quantitative estimates of transport parameters in semiconductor devices

In the recent years the fabrication of sensors and actuator devices on a microscopic scale and their integration with electronic devices and micro-electromechanical systems (MEMS) has become an area of considerable commercial and technological interest, with huge development potentialities. High energy ion microbeam is a suitable tool for such purposes. In this paper we present an alternative way to exploit the lithographic properties of micro ion beams based on the selective damage of silicon to produce porous silicon microstructures. We used a 2 MeV proton microbeam to irradiate definite areas of silicon samples in order to produce damaged layers localised at the end of the proton trajectories. By performing an electrochemical etching in a suitable HF solution, a porous silicon pattern, complementary to the irradiated one, is always formed. The main effect of the damage on the porous silicon formation is to reduce the velocity of formation. To interpret this, such dead layers can be seen to be more or less opaque to the migration of free holes. Consequently the patterned region can be more or less revealed according to the formation time. The procedure allows for the production of microstructures of porous silicon whose unique properties are of great interest for applications. Preliminary results obtained on silicon samples, with different doping levels (p+, p, n+) and irradiating regions with different areas (from 200×200 μm 2 to 25×25 μm 2 ) are presented in order to evaluate the most suitable range of exposure and aspect-ratio of the microstructures.

A new theory is presented concerning both IBIC (ion beam induced charge) and IBIL (ion beam induced luminescence) as obtained by a few MeV ion microbeam of a few micrometers spot size. The theory evidences the fact that IBIL depends on the ratio between the total carrier lifetime and the radiative recombination lifetime. The IBIL/IBIC maps, as obtained by dividing the two average signals pixel by pixel, depend only on radiative lifetime. IBIL maps, as obtained by coincidence measurements in order to avoid electric noise and display regions of low luminescence, compared with IBIC maps, indicate for the first time that regions of long collection length and regions of strong radiative recombination are the most important in CVD diamond. In conclusion, recombination in CVD diamond seems to be mainly radiative.

In this work, we report the analysis of TL features of CVD diamond samples after exposure to 90 Sr/ 90 Yr beta particles. The glow curves have been analysed in order to determine the trapping kinetics and the activation energies of the trapping levels. They have been interpreted as due to a first-order trap emptying process with activation energies ranging from 0.98 to 1.12 eV. Owing to the great practical interest of diamond in radiotherapy, we have explored the application of CVD diamond as TL dosimeter. The dose–response of the CVD diamond film to beta irradiation was investigated at clinical application doses and compared with the response of LiF TL100 samples. Moreover, measurements of charge pulses induced by 5.4 MeV alpha particles were carried out in order to investigate the effect of beta particle pre-irradiation (or ‘priming’) on the charge collection efficiency. The saturation of hole trapping levels evaluated by glow curve analysis was shown to be strictly related to the improvement of charge collection efficiency. A model of the charge carrier dynamics is also presented which accounts for the optical bleaching of glow curve and alpha particle spectra.

Collection efficiency profiles as determined by the ion beam-induced charge (IBIC) technique have been considered to evaluate the spectroscopic performance of a cadmium telluride (CdTe) nuclear radiation detector. The dependence of such profiles on the applied bias voltage and the shaping time are presented and discussed on the basis of a theoretical model, which is also used to evaluate the electron/hole collection lengths profiles. Experimental collection efficiency profiles were used as input data of the “ISIDE” Monte Carlo programme to simulate the CdTe response to gamma rays produced by 57 Co . A systematic investigation of such spectra obtained under different detection conditions shows the effects of non constant collection efficiency profiles and ballistic deficit on the energy resolution of the detector.

Hot filament chemical vapour deposition technique is particularly suitable for the realisation of diamond tip and wire detectors working in a coaxial geometry with a built-in internal metal electrode. By using tungsten wires of different diameters and by controlling the shape of the tip by an electrochemical etch, it is possible to obtain various kinds of microdetectors, with diameters ranging from 50 to 300 μm. The response of these diamond tip and wire detectors has been tested at low X-ray energies (50–250 keV) and at relatively high energies (6–15 MeV) both in terms of sensitivity (collected charge with respect to the absorbed dose) and of linearity as a function of X-ray fluence. Sensitivities larger than 2 nC/Gy are achieved, with a good linearity in the dose rate range used in applications. Such microprobes have been proved to be suitable as narrow X-ray beam profilers and as surface or in vivo microdosimeters for on-line monitoring of radiotherapy plans. Such detectors have also been used as nuclear micro detectors by measuring the response to alpha particles from an 241 Am source and from a proton beam (2.4 MeV energy) produced by a van de Graaff accelerator. In this case the estimated collection efficiency is higher than 20% for wires and 50% for tips.

In this paper the method based on interpreting the data measured within variable angle of incidence spectroscopic ellipsometry and spectroscopic reflectometry is used for the complete optical analysis of hydrogenated amorphous silicon layers deposited on silicon single crystal wafers. This method enables us to perform the analysis of these layers in a relatively wide spectral region because a new model of dispersion of the optical constants of the hydrogenated amorphous silicon layers was constructed. Moreover, the influences of both roughness and native oxide layer existing on the upper boundary of every silicon layer studied is respected at its analysis. The results obtained for a chosen sample of the hydrogenated amorphous silicon layer are presented.

A report is presented concerning the results obtained by Ion Beam-Induced Current (IBIC) investigations about the effects of radiation both on CVD and in natural diamond. Proton microbeam itself is used both to irradiate and to “probe” diamond samples particularly in their cross-sections as obtained by cleaving (“lateral IBIC”). Proton fluences and corresponding doses are limited normally to 108 p/cm2 and to 2 Gy, respectively, leaving the possibility of an order of magnitude more. While in natural IIa diamond samples the charge collection efficiency is homogeneously distributed and it homogeneously increases as a function of proton dose, in CVD diamond samples it is not homogeneously distributed, it reflects the morphology of the samples and the main effect of irradiation is both to increase and to spread it over the low collection efficiency regions. Moreover, transient polarisation effects leading to lower collection efficiencies are reported both for CVD and diamond samples, in a way that seems to be dependent on the count rate registered by the “probe” beam.

Recent progress on developing diamond-based sensors for vertex detection at high luminosity hadron colliders is described. Measurements of the performance of diamond sensors after irradiation to fluences of up to 5/spl times/10/sup 15/ hadrons/cm/sup 2/ are shown. These indicate that diamond sensors will operate at distances as close as 5 cm from the interaction point at the Large Hadron Collider (LHC) for many years at full luminosity without significant degradation in performance. Measurements of the quality of the signals from diamond sensors as well as spatial uniformity are presented. Test beam results on measurements of diamond-based microstrip and pixels devices are described.

The paper reviews measurements of the radiation hardness of CVD diamond for 24 GeV/c proton irradiation at fluences up to 5 ∗ 10 15 protons/cm 2 . The results not only show radiation damage but also an annealing effect that is dominant at levels around 10 15 protons/cm 2 . A model describing both effects is introduced, enabling a prediction of the distribution curve of the charge signal for other levels.

In future HEP accelerators, such as the LHC (CERN), detectors and electronics in the vertex region of the experiments will suffer from extreme radiation. Thus radiation hardness is required for both detectors and electronics to survive in this harsh environment. CVD diamond, which is investigated by the RD42 Collaboration at CERN, can meet these requirements. Samples of up to 2×4 cm 2 have been grown and refined for better charge collection properties, which are measured with a β source or in a testbeam. A large number of diamond samples has been irradiated with hadrons to fluences of up to 5×10 15 cm −2 to study the effects of radiation. Both strip and pixel detectors were prepared in various geometries. Samples with strip metallization have been tested with both slow and fast readout electronics, and the first diamond pixel detector proved fully functional with LHC electronics.

Diamond has many attractive properties which make it an ideal material both for particle detection in high-energy physics experiments and for dosimetry in medical fields. Up to early 1990, diamond has not found widespread applications in these fields because of the high cost and of the difficulties in selecting natural gems of suitable quality, with low levels of impurity content and crystal defects, which limit the carrier lifetime. The recently developed diamond manufacturing technology by chemical vapour deposition (CVD) has the potential of allowing low cost production of diamond in large sheets, with higher purity than natural diamond. In this paper we present a review of the most recent features and applications of CVD diamond as nuclear and X-ray/γ-ray detector.

A full vibronic spectrum has been measured for the first time by LNT Cathodoluminescence in HPHT c-BN amber-coloured microcrystalline samples. The related BN1 centre at 3.293 eV seems not created by electron irradiation in this case and the accurately determined phonon energy (141 ± 3 meV) could be related to LO phonon at X point in Brillouin Zone (BZ) of c-BN, as determined by CL results obtained at indirect gap. Consequently, BN1 centre has not the full cubic symmetry of c-BN, as being due to N interstitials. The interpretation of the results is possibly two-fold: either we are observing a vibronic spectrum with ZPL at BN1 centre, together with other two centres called PF-1 and PF-2 at 3.573 and at 3.412 eV, respectively, or, since all the 6 or 7 observed peaks are exactly equally spaced, the whole vibronic spectrum is related to a ZPL line at 3.573 eV. This new interpretation seems to be in better agreement with the general theory of colour centres.

A proton microbeam has been used to obtain charge collection efficiency maps on cross sections of natural IIa diamond and CVD diamond samples with a sandwich arrangement of electrodes. Particular attention has been dedicated to the dependence of the collection efficiency profiles on bias polarity. Collection efficiency maps may be easily transformed into collection length profiles, giving information about the distribution of mobility and lifetime of carriers and the profile of the electric field. Maps of the proton-induced luminescence have also been obtained. The results confirm the columnar distribution of the charge collection length in CVD diamond, while in natural diamond the distribution is relatively homogeneous.

The charge collection efficiency profile along the thickness of a CdTe detector was measured for first time by using a proton microbeam and a polished cross-section of the devices. Different samples were investigated and tests were carried out along different lines from cathode to anode, with different biases and polarities, and with different shaping times. The effects of all these parameters are evident in the experimental curves. By fitting these curves, the behaviour of the drift length for electrons and holes is obtained, if a constant ratio between them is assumed. If the mobilities and trapping times are uniform, the electric field profile is obtained. The profile has a minimum at the anode and a maximum towards the cathode, at least for large bias voltage.

A non-resonant photoacoustic cell, especially designed to optimize the signal-to-noise ratio, has been built. Following the Rosencwaig and Gersho theory, a new model has been developed for the quantitative determination of the optical absorption coefficient of thermally thick samples, by the simultaneous analysis of the amplitude and the phase of the photoacoustic signal. Tests have been performed on synthetic samples, in order to verify the applicability of the method in the cases of both single and double absorbing layers and a comparison has been carried out with the values of the optical absorption coefficient evaluated by transmission measurements, obtaining an agreement within 5%. The high quality of the response of the cell and the confidence of the method make it suitable for the determination of the optical absorption coefficient of biological samples, that can not be studied with traditional spectroscopic techniques because of their inhomogeneities and complexities. Preliminary results have been obtained on blood and on normal and pathological skin.

Micro-IBIC and micro-PIXE have been used on samples of CVD diamond, CdTe and Si, in order to find correlations between the chemical impurities distribution and the transport properties or collection properties of charge carriers. In CdTe and Si, which are relatively good nuclear detectors, chemical impurities contents are largely below PIXE sensitivity, but micro-IBIC is able to determine the electrical field distribution and the carrier trapping times. In CVD diamond, micro-PIXE maps have been measured for a series of impurities, including both light and heavy elements. These impurities are spread out in regions of low crystallographic order and at grain boundaries, leaving probably the true single crystal unaffected. They should be connected with the large trapping effects measured by micro-IBIC in the same regions.

A 3 MeV proton microbeam has been used for the first time both to investigate the transport properties and to probe the electrical field in a CVD diamond sample of defector grade. Qualitative results concerning the spatial distribution of charge collection efficiency and, consequently, of the collection length are obtained. Collection length seems to be of the order of several tens of microns only in small regions of the same dimensions, characterized probably by a good crystalline behaviour. A strong polarization due to the creation of a local internal electric field and ascribed to the space-charge accumulated in the grain boundaries, makes the measurements very difficult and reduces the statistical validity of the data. However, imaging of physical quantities like collection length is concluded to be a viable technique and it will constitute a useful and powerful method of investigating homogeneity of nuclear detectors and of other similar devices.

Metal-Organic Deposition (MOD) technique has been used for the first time, in the spray version, to obtain thin and thick films of BSCCO on substrates like MgO and Ag and, in the dipping version, to deposit YBCO thick films directly on a thin Ag wire. Diffraction data show that BSCCO films are textured and oriented with their normal axis along the [001] direction. Electron microprobe data confirm a strong presence of (2212) modification of BSCCO. The YBCO/Ag wire is very uniform, as confirmed by SEM micrographs, and shows a transition temperature around 90 K. Thick films and platelets of YBCO have been also prepared by metalorganic solution spraying and by using a commercial microwave oven in the last annealing stage, reducing the duration of this step from several hours to about 65 minutes. YBCO samples show good stoichiometry, a very smooth surface morphology and transition temperatures, as measured by a.c. susceptometry at low magnetic fields, which are around 90 K. Films, deposited on MgO, are oriented with their growth axis along the [005] direction and, if deposited on SrTiO3, along the [006] direction. Physical, chemical, structural and morphological properties of these HTSC samples obtained by MOD are presented and discussed, with the conclusion that this technique, which is simple, flexible, suitable for large surface areas, for ribbons and for wires, has achieved a good stage of maturity.

A new photo-CVD apparatus has been built in order to deposit a-Si: H films and other kinds of amorphous thin films by a technique which is both simple and versatile. This apparatus is composed of three chambers connected together: a load-lock chamber, a process chamber and a third chamber for in-situ analysis of deposited films. A peculiarity of the lamp, a dielectric discharge lamp which can work with noble gases like Xe or Kr, is that it can be completely dismounted without breaking the vacuum in order to clean the optical MgF 2 window. By this method, the deposition chamber can be kept very clean. In this apparatus, we started to deposit a-Si x C 1− x : H of very good quality. These films have been completely characterized by chemical (RBS, ERDA) and optical (PDS) methods. Their quality can be compared with that of a-Si: H samples of the same thickness, obtained by PECVD.

This work reports about experimental findings obtained by means of Modulated Photocurrent (MPC) spectroscopy as applied to a-Si:H films in sandwich configuration. The gap density of states from 0.4 to 0.7 eV below the conduction band edge has been reconstructed for three excitation wavelengths. This allows for a spatial depth profiling of unoccupied defects. It is shown that the defects peak apparently shifts towards midgap when probing the region near a-Si:H-metal interface. This result is interpreted by means of two different models. The likelihood of these models is discussed by comparing the results with other spectroscopic data.

A new photochemical vapor deposition system is used to deposit thin films of hydrogenated amorphous silicon carbon alloys (a-SiC: H). This system employs a newly designed excimer lamp that can work with Ar, Kr, and Xe or a deuterium lamp. The deposition is carried out by means of direct photolysis of Si2H6, avoiding by this way contamination problems connected with the Hg sensitization of the process. The presence of carbon in the films can be related to the presence of fomblin oil on the MgFe2 window. Even if the compositional disorder induced by C atoms is not in principle negligible, the defect density, as inferred by photothermal deflection spectroscopy (PDS), is low, if compared to plasma deposited a-Si: H films with approximately the same thickness. This can be related to the absence of ion bombardment in photoCVD: this peculiarity suggests the possibility of employing photoCVD in the deposition of high quality layers in which the interface states can be dramatically reduced.

Amorphous silicon detectors have been proved to be suitable for charged particles, electrons and minimum ionizing particles. An application which looks very promising is the coupling of a p-i-n a-Si:H detector to a scintillator for X-ray and gamma-ray detection, spectroscopy and imaging. In these cases, a p-i-n detector is used as a PMT, with obvious advantages of minimum space requirements, absence of high voltage bias, insensitivity to magnetic fields and better radiation damage resistance. In the present work, a-Si:H p-i-n detectors have been realized and coupled to various scintillators in order to build X-ray monitors and survey meters. These detectors can work in dc photovoltaic mode with a good sensitivity. The coupling between the detector and the scintillator has been simulated by suitable codes which, starting from the light distribution emitted by the scintillator, evaluate directly the current generated in the photovoltaic detector. The comparison between the calculated response curve, in terms of photocurrent per unit exposure rate as a function of X-ray energy, and the experimental one, is satisfactory. The monitors, particularly with CsI(Tl), have been tested under exposure rates between 1 and 103 R min−1 in the energy range 20–150 keV. The possibility of realizing matrix or pixel structures either with position sensitivity or effective energy determination capability by using filter sets has been indicated and it is under development.

Optoelectronic and structural properties of thin, hydrogenated amorphous silicon samples grown by thermal decomposition of disilane in different positions along a low pressure chemical vapour deposition reactor are investigated by means of infrared spectroscopy, Raman scattering, and photothermal deflection spectroscopy. Correlations between the character and the hydrogen content versus density of states and between the hydrogen bonding configuration versus transverse optical/acoustic phonon modes are found. The purely thermal excitation of gas molecules gives rise to an amorphous material with a rather low density of states. Samples grown at different positions inside the reactor show different hydrogen concentration and bonding configuration, bond angle deviation, Urbach tail slope, and density of states. The most important parameters governing the LPCVD of a-Si: H are discussed. Optoelektronische und Struktureigenschaften von dunnen, hydrogenisierten, amorphen Siliziumproben, die durch thermische Zersetzung von Silan an verschiedenen Stellen im Reaktor fur Niederdruckabscheidung aus der Dampfphase (LPCVD) hergestellt wurden, werden mittels Infrarotspektroskopie, Ramanstreuung und photothermischer Abscheidungsspektroskopie untersucht. Korrelationen zwischen Charakter und Wasserstoffgehalt und der Zustandsdichte sowie zwischen der Wasserstoffbindungskonfiguration und den transversal optischen/akustischen Phononenmoden werden aufgedeckt. Die rein thermische Anregung von Gasmolekulen fuhrt zu amorphem Material mit relativ geringer Zustandsdichte. Die an verschiedenen Stellen innerhalb des Reaktors gewachsenen Proben zeigen Unterschiede in Wasserstoffkonzentration und Bindungskonfiguration, Abweichung des Bindungswinkels, Steigung des Urbach-Auslaufers und Zustandsdichte. Die wichtigsten Parameter, die Einflus auf die LPCVD von a-Si haben, werden diskutiert.

Large area 4H-SiC Schottky diodes equipped with a 6LiF converter were tested as neutron detectors in the epithermal column realized for Boron Neutron Capture Therapy (BNCT) applications at the fast reactor TAPIRO (ENEA Casaccia Roma). The neutron spectra were assessed using the Monte Carlo code MCNP-4C. The performances of SiC detectors were evaluated with neutron fluences in the range of 109–1013 cm−2 which is typical for BNCT. Spectra of alpha and tritium particles generated by 6Li(n,α)3H reaction were collected at various neutron fluences and spectra obtained by interposing polyethylene moderators of different thickness. Only weak damaging effects primarily due to the alpha particles were observed; at neutron fluence of 1013 cm−2 the count rate decreased by

An extended vibronic spectrum (up to six phonon replicas) has been measured by low temperature cathodoluminescence in pure c-BN microcrystalline samples obtained by high temperature high pressure method. The zero phonon line, found at $3.573\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, should be connected to a center identified previously as PF1, which is intrinsic in c-BN. As a consequence, the vibronic spectrum is not associated with the BN1 center at $3.293\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, which is created by irradiation, as reported in literature. The spectrum is in very good agreement with the Franck-Condon model, formerly developed for color centers in alkali halides and from which in this case a value of 5.26 for the Huang-Rhys factor can be obtained. From the spectrum it has been possible to determine very precisely the value of phonon energy $(141\ifmmode\pm\else\textpm\fi{}3\phantom{\rule{0.3em}{0ex}}\mathrm{meV})$, which is in good agreement both with the results of ab initio calculations of LO phonon energy at the $X$ point of the Brillouin zone of c-BN and with the value measured by second-order Raman spectroscopy. The connection of this center with the indirect gap and the large energy threshold for excitation could explain why this center with its vibronic band was hardly seen before by photoluminescence. Since the measured displacement of the equilibrium normal coordinate of the excited level was found to be $0.17\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, this level could be attributed, according to calculations from first principles, to a boron antisite and not to a Frenkel pair (a nitrogen vacancy coupled to a boron interstitial) as previously indicated.

Progress in experimental particle physics in the coming decade depends crucially upon the ability to carry out experiments in high-radiation areas. In order to perform these complex and expensive experiments, new radiation hard technologies must be developed. This paper discusses the use of diamond detectors in future tracking applications and their survivability in the highest radiation environments. We present results of devices constructed with the newest polycrystalline and single crystal Chemical Vapor Deposition diamond and their tolerance to radiation.

The damage produced by 2 MeV protons on a 4H-SiC Schottky diode has been investigated by monitoring the charge collection efficiency as the function of the ion fluence. A new algorithm based on the Shockley-Ramo-Gunn theorem has been developed to interpret the experimental results. The fitting procedure provides a parameter which is proportional to the average number of active electrical traps generated by a single ion, which can be profitably used to estimate the radiation hardness of the material.

The envisaged upgrade of the Large Hadron Collider (LHC) at CERN towards the Super-LHC (SLHC) with a 10 times increased luminosity of 1035 cm-2 s-1 will present severe challenges for the tracking detectors of the SLHC experiments. Unprecedented high radiation levels and track densities and a reduced bunch crossing time in the order of 10 ns as well as the need for cost effective detectors have called for an intensive R&D program. The CERN RD50 collaboration ''Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders'' is working on the development of semiconductor sensors matching the requirements of the SLHC. Sensors based on defect engineered silicon like Czochralski, epitaxial and oxygen enriched silicon have been developed. With 3D, Semi- 3D and thin detectors new detector concepts have been evaluated and a study on the use of standard and oxygen enriched p-type silicon detectors revealed a promising approach for radiation tolerant cost effective devices. These and other most recent advancements of the RD50 collaboration are presented.

An option of increasing the luminosity of the Large Hadron Collider (LHC) at CERN to 10^35 cm^(- 2) s(- 1) has been envisaged to extend the physics reach of the machine. An efficient tracking down to a few centimetres from the interaction point will be required to exploit the physics potential of the upgraded LHC. As a consequence, the semiconductor detectors close to the interaction region will receive severe doses of fast hadron irradiation and the inner tracker detectors will need to survive fast hadron fluences of up to above 1016 cm 2. The CERN-RD50 project ''Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders'' has been established in 2002 to explore detector materials and technologies that will allow to operate devices up to, or beyond, this limit. The strategies followed by RD50 to enhance the radiation tolerance include the development of new or defect engineered detector materials (SiC, GaN, Czochralski and epitaxial silicon, oxygen enriched Float Zone silicon), the improvement of present detector designs and the understanding of the microscopic defects causing the degradation of the irradiated detectors. The latest advancements within the RD50 collaboration on radiation hard semiconductor detectors will be reviewed and discussed in this work.

Semiconductor detectors equipped with a converter like 6 LiF or 10 B can currently be considered a very interesting alternative to conventional neutron detectors, especially because of their compactness and reliability. The materials for the detection of the ions produced in the converter are generally either Si or GaAs. SiC detectors presented in this work are completely new devices which are proved to be very suitable for neutron detection, dosimetry and beam monitoring. Their capability to withstand high radiation doses should largely overcome the performances of Si and GaAs; moreover, because of the lower Z value, gamma-ray discrimination turns out to be more efficient. In this work, the results obtained with a series of large-area epitaxial SiC Schottky barrier detectors will be presented and discussed.

Simulation of gamma-ray semiconductor detector generally makes assumptions such as electric field uniformity, constancy of mobilities and trapping times respect to electric field, etc. At least a part of these assumptions are not valid. A way to overcome this problem is to measure the collection efficiency as a function of depth directly. By a particular version of the micro-IBIC technique we measured the collection efficiency on a section of a CdTe detector and we used the experimental data as input for the Monte Carlo code ISIDE for simulating pulse height spectra produced by 57Co. The results obtained by this more realistic approach are presented and can be compared both with other kinds of simulations and with available experimental data.