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Silicon nanowires physical properties strongly depend on their growth conditions, as already assessed. We report on the electrical properties of nanowires (NWs) grown by the vapor–liquid–solid (VLS) mechanism, one of the most established for NW growth, and by the more recent metal-assisted wet chemical etching (MaCE). Wet etching growth process promises to be an industrial advantageous way for growing Si NWs, because of its cheapness, fastness, relative easiness. The electronic level scheme in VLS grown, boron (B)- and phosphorus (P)-doped NWs has been experimentally investigated. We have demonstrated that the doping impurities induce the same shallow levels as in bulk silicon. The presence of two donor levels in the lower half-bandgap is also revealed, which has been successfully related to VLS growth details. We report, also, on the first results on the physical properties of Si NW arrays grown by MaCE, and compare them to those of VLS grown Si NWs.

Studies were performed on two types of chlorine-compensated cadmium telluride crystals with a different density of native dislocations walls. The crystals were investigated by current–voltage measurements, photo-induced current transient spectroscopy and absorption measurements, in the view of investigating the influence of the density of dislocation walls on their charge transport properties and electronic levels scheme. It results that a higher density of dislocation walls increases the dark current in CdTe. To the contrary, the optical absorption properties do not seem to be influenced by the presence of dislocation walls. The PICTS measurements demonstrated that a lower density of dislocation walls provides a higher concentration of compensation-related defects and a lower concentration of the defects responsible for the peaks observed at high temperature, possibly associated to donor-pair complexes.

We studied the anisotropic charge transport properties of solution-grown organic single crystals based on a dipolar molecule 4HCB (4-hydroxy-cyanobenzene) by electrical transport measurements, current-voltage and space charge limited current (SCLC), and by X-ray diffraction analyses.Optical excitation differently affects the flow of charge carriers along the two main planar crystal axis, altering the charge transport anisotropy induced by the molecular π-orbitals stacking. We attribute this behaviour to the presence of an intrinsic molecular dipole and to its different orientation within the crystal lattice. The anisotropy of transport along the three crystallographic directions has been assessed by electrical characterization and correlated to the crystal molecular packing as determined by X-ray analyses.

Fully-encapsulated CZT crystals were grown by vertical Bridgman technique using boron oxide as encapsulant for preventing material decomposition. To detect possible effects of boron on the crystal microstructure, we performed current-voltage measurements and Photo-Induced Current Transient Spectroscopy measurements on samples grown by boron oxide encapsulated vertical Bridgman (set EVB) and standard vertical Bridgman (set VB). In both sets, the well-known A-center and a midgap trap dominate the PICTS spectra. However, significant differences are evident, related to the different defect contents. Our findings indicate that most of the boron atoms are electrically inactive and do not affect the transport properties of the material, confirming that boron oxide vertical Bridgman technique can be adopted for the growth of detector grade CZT crystals.

The huge amount of knowledge, and infrastructures, brought by silicon (Si) technology, make Si Nanowires (NWs) an ideal choice for nano-electronic Si-based devices. This, in turn, challenges the scientific research to adapt the technical and theoretical paradigms, at the base of established experimental techniques, in order to probe the properties of these systems. Metal-assisted wet-Chemical Etching (MaCE) [1, 2] is a promising fast, easy and cheap method to grow high aspect-ratio aligned Si NWs. Further, contrary to other fabrication methods, this method avoids the possible detrimental effects related to Au diffusion into NWs. We investigated the bandgap level diagram of MaCE Si NW arrays, phosphorous-doped, by means of Deep Level Transient Spectroscopy. The presence of both shallow and deep levels has been detected. The results have been examined in the light of the specificity of the MaCE growth. The study of the electronic levels in Si NWs is, of course, of capital importance in view of the integration of Si NW arrays as active layers in actual devices.

Despite a high dislocation density and a strong polarization effect, during the past two decades, Gallium Nitride (GaN) based Light Emitting Diodes (LEDs) have emerged as solid state light sources in the spectral range from visible to ultraviolet. InGaN/GaN based Multiple Quantum Wells (MQWs) are employed as active layers in GaN based LEDs. It is well known that due to the lack of native substrates, GaN based devices are usually grown heteroepitaxially on substrates such as sapphire, resulting in a high density of Threading Dislocations (TDs) (~108 cm-2 – 109 cm-2) which traverse vertically from the substrate to the epilayer surface1. In addition, the surface defects such as V shaped defects and trench defects2,3 have also been observed in InGaN QW structures grown by Metal Organic Vapor Phase Epitaxy (MOVPE). These defects as a whole have a deleterious impact on the performance of LED Devices4,5. In earlier studies it was believed that the dislocations do not contribute to the electronic states of GaN and are electrically inert6,7. Recent findings have shown that the TDs can be optically and electrically active8. It is also reported that screw and mixed TDs act as non radiative recombination centres while the edge TDs are optically inert9. However, the effects of these defects on the electrical and optical properties of LED devices are still not fully understood. In this paper, we investigated a GaN based blue LED structure, containing a high density of dislocations, in order to get information about the effect of these dislocations on the micro structural, electronic and optical behaviours of these LEDs. The present work reports on the characterization of InGaN/GaN based LED structures by Atomic Force Microscope (AFM), which aimed at the detailed study of surface morphology and defect structures. The electrical properties of defects were studied by Electron Beam Induced Current (EBIC) and the luminescence properties of these LEDs were studied by Electroluminescence (EL).

Deep Level Transient Spectroscopy was performed on InGaN/GaN multiple quantum well (MQW) light emitting diodes (LEDs) in order to determine the effect of the dislocation density on the deep intragap electronic levels. The LEDs were grown by Metalorganic Vapor Phase Epitaxy (MOVPE) on GaN templates with a high dislocation density (HDD) of 8x109 cm-2 and a low dislocation density (LDD) of 3x108 cm-2. Three trapping levels for electrons were revealed, named A, A1 and B, with energies EA ≈ 0.04 eV, EA1 ≈ 0.13 eV and EB ≈ 0.54 eV, respectively. The trapping level A has a much higher concentration in the LEDs grown on the template with a high density of dislocations. The logarithmic dependence of the peak amplitude on the bias pulse width for traps A and A1 identifies the defects responsible for these traps as associated with linearly arranged defects. We conclude that traps A and A1 are dislocation-related intragap energy levels.

This paper explores the cold field emission (CFE) properties of SiC nanowire (NW) arrays. The CFE currents were studied in the dark and under ultra-violet (UV) irradiation conditions. An increase in CFE current was observed when the SiC NW arrays were illuminated, with a consequent decrease in the values of the turn-on field and the threshold field. Furthermore, while dark CFE currents were well described by the standard Fowler–Nordheim (FN) theory for metals, the photo-enhanced CFE currents showed nonlinearity in FN plots. Specifically, a voltage range of current saturation appeared, which is appealing for nanotechnological applications, and it is indeed an essential prerequisite for realizing devices such as FE photocathodes.

Silicon nanowires (Si NWs) are widely investigated nowadays for implementation in advanced energy conversion and storage devices, as well as many other possible applications. Black silicon (BSi)-NWs are dry etched NWs that merge the advantages related to low-dimensionality with the special industrial appeal connected to deep reactive ion etching (RIE). In fact, RIE is a well established technique in microelectronics manufacturing. However, RIE processing could affect the electrical properties of BSi-NWs by introducing deep states into their forbidden gap. This work applies deep level transient spectroscopy (DLTS) to identify electrically active deep levels and the associated defects in dry etched Si NW arrays. Besides, the successful fitting of DLTS spectra of BSi-NWs-based Schottky barrier diodes is an experimental confirmation that the same theoretical framework of dynamic electronic behavior of deep levels applies in bulk as well as in low dimensional structures like NWs, when quantum confinement conditions do not occur. This has been validated for deep levels associated with simple pointlike defects as well as for deep levels associated with defects with richer structures, whose dynamic electronic behavior implies a more complex picture.

We report the first observation of the electronic level scheme in boron (B)- and phosphorus (P)-doped nanowires (NWs). The NWs’ morphology dramatically depends on the doping impurity while a few deep electronic levels appear in both kinds of nanowires, independently of the doping type. We demonstrate that the doping impurities induce the same shallow levels as in bulk silicon. The presence of two donor levels in the lower half-bandgap is also revealed. In both kinds of NWs, B- and P-doped, the donor level (0/ +) at Ev + 0.36 eV of the gold−hydrogen complex is observed. This means that the gold diffusion from the NW tip introduces an electronically active level, which might negatively affects the electrical characteristics of the NWs. In P-doped NWs, we observed a further donor level at 0.26 eV above the valence band due to the phosphorus-vacancy pairs, the E-center, well-known in bulk silicon. These findings seriously question both diffusion modeling of impurities in NWs and the technological aspects arising from this.

Silicon edgeless detectors represent a novel type of detector that are being developed for close-to-beam applications in high-energy physics and for large-scale tiled 1D and 2D arrays used in radiation imaging. In this work, the electric field and potential distributions on the device cut side, key factors in detector performance, have been investigated using two methods—the Conductive Microprobe Technique and the Scanning Transient Current Technique. It has been found that the behaviour of the potential distribution at the edge indicates a significant presence of positively charged states, with the charge density changing with the applied voltage. This work will predict, to a first approximation, the trend of the electric field at the edge of these devices after irradiation to high fluences. This prediction will provide key inputs in the development of edgeless radiation hard detectors.

Traps are characterized in AlGaN–GaN HEMTs by means of DLTS techniques and the associated charge/discharge behavior is interpreted with the aid of numerical device simulations. Under specific bias conditions, buffer traps can produce “false” surface-trap signals, i.e. the same type of current-mode DLTS (I-DLTS) or ICTS signals that are generally attributed to surface traps. Clarifying this aspect is important for both reliability testing and device optimization, as it can lead to erroneous identification of the degradation mechanism, thus resulting in wrong correction actions on the technological process.

It is demonstrated that boron-doped nanowires have predominantly long-term stable wurtzite phase while the majority of phosphorus-doped ones present diamond phase. A simplified model based on the different solubility of boron and phosphorus in gold is proposed to explain their diverse effectiveness in retaining the wurtzite phase. The wurtzite nanowires present a direct transition at the Γ point at approximately 1.5 eV while the diamond ones have a predominant emission around 1.1 eV. The aforementioned results are intriguing for innovative solar cell devices.

This paper reports on the defects created in a 6H-SiC p-type substrate by a process of ion implantation and a quite low temperature annealing (1300 °C), suitable for the realization of the source/drain regions of a MOSFET because it does not give rise to step bunching phenomena. Current voltage measurements showed the presence of a group of diodes featured by excess current. The effects of defects under the implanted layer on the transport properties of the diodes were investigated by DLTS: four hole traps were detected in all the measured diodes; besides, a broadened peak around 550 K was detected in the diodes that show excess current.

Spectral photoconductivity is a very efficient tool to explore the forbidden gap of wide gap semiconductors, detecting band-to-band or deep level-to-band transitions of the charge carriers. In this paper we present some results obtained by spectral photoconductivity concerning HVPE (hydride vapour phase epitaxy) grown gallium nitride submitted to high energy proton irradiation. The behaviour of the material before and after irradiation may give information on the characteristics of the deep bands and their association to surface or bulk defects. In particular we observed how irradiation quenches the yellow band and correspondingly inhibits persistent photocurrent effects. Persistent photocurrent measurements carried out at different temperatures give further insights on the radiation-induced effects. The possible correlation among the deep-related transitions and the persistent photo-effects is here proposed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effects of irradiation with protons and electrons on 4H-silicon carbide epilayers were investigated. The particle energy was 6.5 and 8.2 MeV. The electronic levels associated with the irradiation-induced defects were analyzed by current-voltage characteristics and deep level transient spectroscopy measurements up to 700 K. In the same temperature range the apparent free carrier concentration was measured by capacitance-voltage characteristics to monitor possible compensation effects due to the deep level associated to the induced defects. Introduction rate, enthalpy and capture cross-section of such deep levels were compared and some conclusions about the nature of the defects were drawn.

This contribution reports the study, by junction spectroscopies, of electronic states induced by thermal and deformation treatments in p-type Si. In order to understand the role that oxygen precipitation, metallic contamination and plastic deformation play on the defect states, several sets of Cz (Czochalski) and Fz (Float-zone) Si samples and different material treatments were investigated. The electronic states were also compared with optical transitions obtained by photoluminescence analyses carried out on the same sample sets. These defect states could thus be microscopically identified with specific defect types.

In this contribution the field emission by tunneling of electrons of 3C-SiC nanowires on Si substrate, grown by CVD method via Ni catalyst, has been investigated. Scanning electron images have quantified the low density of the nanowires over the sample surface. In order to exclude any contribution to the Field Emission phenomenon from the Si substrate, the field emission measurements have been performed before and after removing the SiC nanowires. The Field Emission experiments have been carried out in dark conditions and by shining the sample surface. The extracted Fowler-Nordheim (F-N) plots show that the Field Emission from nanowires is highly sensitive to illumination parameters. When using lighting, a partition in three regions of the F-N plot has been observed. In the low field region, the F-N plot is linear or metallic-like, then it follows a saturation-current region and finally the high field region is characterized by a sharp increase. Departure from the standard F-N theory, that is the influence of light and temperature on the Field Emission phenomenon, is well assessed for bulk semiconductor cathodes [1], but it has been rarely observed in single SiC nanowires [2]. To the authors’ knowledge, this contribution reports for the first time the strong deviation from F-N linear behavior for multiple SiC nanowires dispersed over planar substrate. Field Emission data from quantum-confined structures are both useful for the study of their fundamental physics, but also because of promising technological applications, such as electron sources, high-resolution electron beam instruments, and Field Emission displays. [1] G. N. Fursey, Field Emission in Vacuum Microelectronics (Kluwer Academic, New York, 2005) [2] M. Choueib , A. Ayari, P. Vincent, M. Bechelany, D. Cornu, and S. T. Purcell, "Strong deviations from Fowler-Nordheim behavior for field emission from individual SiC nanowires due to restricted bulk carrier generation", Physical Review B 79, 075421 (2009)

The presence of defects on 4H-SiC wafers was carefully evidenced by different kinds of techniques such as optical microscopy and scanning electron microscopy. Highlighted defects were also analyzed by atomic force microscopy and profilometer technique and the presence of different SiC polytypes inclusions was found by Raman spectroscopy. Schottky diodes were realized on investigated wafers in order to obtain informations about the correlation between defects and electrical properties of the devices. Electrical characterization has shown the influence of defects in voltage reverse breakdown and Deep Level Transient Spectroscopy has evidenced the presence of two main centers of recombination.

Deep level transient spectroscopy(DLTS) and capacitance-voltage (C-V) characteristics were used to investigate the effects induced by electron irradiation on the majority carrier traps in Schottky diodes prepared on 4H silicon Carbide (SiC) epilayers grown by chemical vapour deposition (CVD). Electron beam induced current (EBIC) method was applied to measure the change in minority carrier diffusion length L related to the generation of traps by electron irradiation. Several energy levels were detected and their concentration monitored as a function of the irradiation dose. The correlation with the diode charge collection efficiency is also reported.

In spite of the high potentiality of silicon carbide (SiC), its technology shows at the moment some limitations, due to the defects present in the crystalline structure. We have focused our analysis on commercial 4H–SiC epitaxial layers. A preliminary investigation has been performed by Optical and Scanning Electron microscopies with the aim to evidence the defect morphology on a large scale. An insight on the defect structure has been obtained by Atomic Force Microscopy, profilometer technique, Micro-Raman and Micro-Photoluminescence spectroscopies. Different types of defects such as comets, super dislocations, etch pits and so on, have been characterized finding interesting peculiarities such as different polytypes inclusions. Moreover, the influence of such defects on the SiC electrical performance has been deeply analyzed through the realization of Schottky barriers onto SiC regions including specific kinds of defects, then performing electrical characterization such as current–voltage (I–V) analysis. Deep Level Transient Spectroscopy (DLTS) yielded the energy position in the SiC gap, the concentration and the capture cross section of two center of recombination.

This paper presents failure modes observed in long-term aging of high-brightness GaN/InGaN LEDs. The blue LEDs submitted to DC aging test present large decrease of emitted optical power and increase of diode reverse leakage current. Increase of parasitic series resistance, suggesting contact degradation, has also been found in stressed sample, together with apparent carrier density increases and reduction of the junction depletion width. Furthermore stressed LEDs present modification of a specific trap property: trap activation energy decreases from 340 meV in the virgin sample down to 75 meV in the stressed sample. Generation of non-radiative recombination centers seems to be one of the dominant failure mechanisms responsible for the observed electrical and optical LED degradations.

The electronic properties of the recombination centres responsible for radiative and non-radiative recombination processes in silicon are studied by injection-level-dependent diffusion length measurements. Measurements were performed, using a spectral response method, on Czochralski silicon samples heat treated at 470°C for different times in order to induce the thermal donor formation. The analysis of the injection level dependence of the carrier diffusion length using the Shockley–Read–Hall theory shows that the two fundamental recombination centres in these samples have an energy level located at 0.37 eV from the valence band and at 0.34 eV from the conduction band. The former centre is also responsible for the presence of the P line in the photoluminescence spectra. These results are in agreement with deep-level transient spectroscopy measurements carried out on the same samples.

The study of the effect of extended defects, present in very large numbers in GaN epilayers, on the material properties and device performance is one of the most important aims of the current research in the field of III nitrides. Thickness strongly influences electrical and optical properties of epitaxially grown GaN. Due to the lattice mismatch between sapphire and GaN, extended defects (mainly threading dislocations) are generated at the sapphire/epilayer interface, and a degenerate layer, characterized by high defect density and high conductivity, has been observed. Moving toward the top surface, the density of the extended defects, which seem to greatly affect the material properties, gradually decreases. This fact mainly causes the commonly observed electrical and optical inhomogeneities. This work deals with the comparative study by means of optical and electrical characterization between two HVPE-grown layers with different thickness (2.6 and 55 μm) in order to check the effects of the extended defect distribution across the sample.

Acceptor deactivation in the near-surface region of as-grown, boron-doped Si wafers was detected by in-depth profiles of the free-carrier density obtained by capacitance–voltage measurements. As this deactivation was only observed in wafers subjected to the standard cleaning procedures used in Si manufacturing, we ascribed it to boron passivation by an impurity introduced during the cleaning process. From the study of the free-carrier reactivation kinetics and of the diffusion behaviour of boron–impurity complexes, we have concluded that the impurity is possibly related to hydrogen introduced during the cleaning treatments. The characteristics of the deep level associated with this impurity have been analysed by deep-level transient spectroscopy.

The performance of photovoltaic devices is greatly influenced by the surface characteristics such as surface roughness and presence of organic contaminants; therefore, their measurement is of great importance for photovoltaic industry. Moreover, these parameters should be measured by non-contact, fast methods capable of application as in-line techniques in photovoltaic industry. Surface roughness measurements and detection of organic contaminants by work-function measurements are the subject of this contribution. Monocrystalline and multicrystalline silicon wafers have been analyzed by Scanning Kelvin Probe (SKP ) in order to obtain work-function maps. These presented regions of higher work-function values correspond to organic contaminants, which are deliberately deposited on the wafer surface. In this way we have demonstrated the capability of work-function measurements for the detection of the contaminants. Moreover, unintentional organic contamination has been detected on multicrystalline Si wafers by SKP analyses. At the same time, the surface roughness has been obtained from surface topography maps.

Scanning Kelvin Probe (SKP) and Surface Photovoltage (SPV) methods have been implemented on the same stage in order to get information on surface, as well as on bulk, electronic properties of multi-crystalline Si wafers. The two probes allow for the measurements of three different parameters: the diffusion length, the majority carrier distribution and the work function differences over the whole wafer area in non-contact and non-destructive way, and no wafer preparation is required. Examples of the application of these methods for the characterization of multi-crystalline wafers for photovoltaic applications will be presented.

Technological improvement of GaN-based devices for electronic and optoelectronic applications makes essential both monitoring and controlling point and extended defects, which can have detrimental effects in device performance. For gallium nitride, thickness is a key parameter controlling the density and distribution of defects, especially extended ones. In this work highly defective thin GaN layers, both p- and n-type, have been characterized by photocurrent (PC) and time-resolved cathodoluminescence (TRCL) spectroscopy in order to evidence the presence of defect-related bands influencing the electrical and optical activity of the material. Scanning microscopy-based techniques, namely electron beam induced current (EBIC), CL imaging and optical beam induced current (OBIC) have been applied to investigate the recombination activity and the spatial distribution of the extended defects.

Native or process-induced defective states may significantly affect the transport properties of silicon carbide devices. For this reason, it is of major importance to detect them and, when possible, to identify their origin. This contribution deals with the deep levels detected by deep level transient spectroscopy analyses in silicon carbide Schottky detectors. Current–voltage and capacitance–voltage characteristics have also been studied to investigate Schottky barrier properties and diode quality. On the basis of the comparison with literature data, some of the deep levels found can be attributed to impurities introduced during growth.

Particle irradiation causes dramatic changes in bulk properties of p + –n–n + silicon structures operating as particle detectors. Several attempts to model and justify such variations have been proposed in the last few years. The main unsolved problem remains in the determination of the electric field and depletion layer distributions as key-parameters to estimate the collection efficiency of the detector. By using optical beam induced current (OBIC) and surface potential (SP) measurements we determined the behavior of the electric field and confirmed the existence of a double-junction structure appearing after irradiation.

In the past few years, a large body of work has been dedicated to CdTe thin film semiconductors, as the electronic and optical properties of CdTe nanostructures make them desirable for photovoltaic applications. The performance of semiconductor devices is greatly influenced by the deep levels. Knowledge of parameters of deep levels present in as-grown materials and the identification of their origin is the key factor in the development of photovoltaic device performance. Photo Induced Current Transient Spectroscopy technique (PICTS) has proven to be a very powerful method for the study of deep levels enabling us to identify the type of traps, their activation energy and apparent capture cross section. In the present work, we report the effect of growth parameters and LASER irradiation intensity on the photo-electric and transport properties of CdTe thin films prepared by Close-Space Sublimation method using SiC electrical heating element. CdTe thin films were grown at three different source temperatures (630, 650 and 700 °C). The grown films were irradiated with Nd:YAG LASER and characterized by Photo-Induced Current Transient Spectroscopy, Photocurrent measurementand Current Voltage measurements. The defect levels are found to be significantly influenced by the growth temperature.

The behaviour of β-Ga2O3 nanowires as photoconductive material in deep ultraviolet photodetectors to operate in the energy range 3.0–6.2 eV has been investigated. The nanowires were grown by a catalyst-free thermal evaporation method on gallium oxide substrates. Photocurrent measurements have been carried out on both undoped and Sn-doped Ga2O3 nanowires to evidence the influence of the dopant on the photodetector performances. The responsivity spectrum of single nanowires show maxima in the energy range 4.8–5.4 eV and a strong dependence on the pulse frequency of the excitation light has been observed for undoped nanowires. Our results show that the responsivity of β-Ga2O3 nanowires can be controlled by tuning the chopper frequency of the excitation light and/or by doping of the nanowires. Non-linear behaviour in characteristic current–voltage curves has been observed for Ga2O3 : Sn nanowires. The mechanism leading to this behaviour has been discussed and related to space-charged-limited current effects. In addition, the responsivity achieved by doped nanowires at lower bias is higher than for undoped ones.

OBIC analyses of particle detectors are presented. The depletion layer width W of semi-insulating gallium arsenide Schottky detectors versus biasing has been studied and it is concluded that at high voltages W linearly increases with the applied bias. Furthermore, the electric field distribution in silicon p-i-n detectors has been investigated before and after heavy irradiation and a V-shaped distribution has been assessed.

The electrical activity of the defective states in Er-doped Si has been investigated. The epitaxial layer of Si:Er was grown with the liquid-phase epitaxy method and showed optical emission at 1.54μm. The presence and activity of dislocations have been evidenced by the appearance of lines D1 and D2 in photoluminescence spectra and it has been confirmed by spectroscopic investigations of the existing deep levels, carried out by deep-level transient spectroscopy and optical deep-level transient spectroscopy analyses. We also characterized the defective states by means of charge collection scanning microscopy, namely the electron-beam-induced current (EBIC) and optical-beam-induced current (OBIC) techniaues. The minority-carrier diffusion length has been measured with the EBIC method. OBIC images reveal interesting lattice sites where local emission of charge carriers occurs.

Hydride vapor phase epitaxy GaN layers were studied by electron beam induced current (EBIC), cathodoluminescence (CL) and scanning photoluminescence (SPL). Both blue and yellow luminescence distributions were studied, showing spatial correlation. CL and EBIC images revealed a granular structure with grain sizes around 1 μm. The minority carrier diffusion length was measured obtaining values around 0.5–0.8 μm, which were correlated to the size of the bright grains observed in EBIC and CL images.

Semi-insulating, undoped, Liquid Encapsulated Czochralski (SI-U LEC) GaAs detectors have been irradiated with 24 GeV/c protons at the fluence of 5.6×1013 p/cm2. The detector charge collection efficiency, cce, for both electrons and holes is remarkably reduced after irradiation while the reverse current increases. The effect of annealing the detectors at temperatures ranging from 220 °C to 280 °C has been seen to reduce the reverse current and to increase the electron cce, while the recovery of the hole cce is negligible in irradiated detectors. Deep electron traps have been followed in their evolution with the heat treatment temperature by P-DLTS and C-V measurements. They recover by increasing the heat treatment temperature and this can explain the restoration observed in electron cce.

In this paper we report a systematic investigation the nature and energy levels of traps generated during the segregation in oxygen of silicon wafers submitted to a two-step annealing sequence, the first of which is carried out at 470°C and the second at temperatures ranging from 600 to 800°C. The investigation was carried out by using DLTS (deep level transient spectroscopy) and optical DLTS at temperatures ranging from liquid He to room temperature. The main result of our work was the discovery of clear correlations between the annealing sequence and the concentration and nature of traps. In fact, a spectrum of shallow levels was found in samples presenting a high density of thermal donors (TD), whose intensity decreases as soon as the density of TD decreases. Also, the precipitation of oxygen as an (amorphous) oxide, presenting an average size of 2 nm, is associated to the presence of traps which are assigned in literature to dislocations in samples submitted to deformation. In our case, dislocations originate from interstitials ejected during the segregation of the oxide phase, which is known to be a volume exigent process.

The effect of irradiation on semi-insulating gallium arsenide Schottky diodes has been investigated by means of surface potential measurements and spectroscopic techniques. Before and after irradiation the electric field exhibits a Mott barrier-like distribution, and the box-shaped space charge modifies its distribution with irradiation. The increase in density or the generation of some traps changes the compensation ratio producing a deeper active region and a more homogeneous distribution of the electric field. The latter phenomenon is also observed by EBIC images of edge-mounted diodes.

Electron beam induced current (EBIC) technique is successfully used to characterize intrinsically gettered Czochralski silicon. The impact of three different sequences of thermal treatments, typically used in ultralarge scale integration device manufacturing, on the denuded zone (DZ) formation and oxygen precipitation in the bulk is evaluated. EBIC technique is applied in a nonstandard configuration, where a Schottky diode is evaporated on the wafer cross section, for the direct observation of the DZ and oxygen related defects in the silicon bulk. The reduction of minority carrier diffusion length, due to the formation of recombination centers after oxygen precipitation, is also estimated by EBIC in planar collector geometry. The DZ determination by EBIC technique is in good agreement with surface photovoltage measurements and microscopical inspections after chemical etching.

The behavior of the active region width W of semi-insulating gallium arsenide Schottky diodes versus reverse biasing has been investigated by optical beam induced current and surface potential techniques. It has been found that at low applied voltages, W follows the square root law peculiar to a Schottky barrier while, for a bias higher than 20 V, the active layer increases linearly with the voltage applied. To go deeper into this matter, the spatial distribution of the electric field has been analyzed in a wide range of bias voltages and it has been observed that at high voltages a plateau occurs, followed by a linear decrease down to a quasi-zero value. In terms of space charge distribution this means that there is a box-shaped space charge region moving towards the ohmic contact at increasing bias.

The deep levels present in semiconducting CdTe and semi-insulating CdTe:Cl and Cd0.8Zn0.2Te have been investigated by means of cathodoluminescence, deep level transient spectroscopy (DLTS), photo-induced current transient spectroscopy, and photo-DLTS. The latter two methods, which can be applied to semi-insulating materials, allow to characterize the deep traps located up to midgap and can determine whether they are hole or electron traps. We have identified 12 different traps, some common to all the investigated samples, some peculiar to one of them. A comparison of the results obtained from the various materials is given and the status of defect models is reviewed.