B. Fraboni

Deep energy levels in CdTe and CdZnTe

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.

Layout reconstruction of complex silicon chips

A semiautomated, fast-turnaround and high-reliability procedure for the layout reconstruction of complex VLSI circuits is presented together with details of the equipment and processes employed. The techniques have been verified using both simple CMOS gate array chips and complex VLSI microprocessor circuits and may be applied, in principle, to arbitrarily large or complex devices. >

Comparison of electrical and luminescence data for the A center in CdTe

We have investigated the electrical and optical properties of the deep levels responsible for the 1.4–1.5 eV luminescence band usually observed in II–VI compounds. We compared the energy levels found by cathodoluminescence and junction spectroscopy methods for semi‐insulating (CdTe:Cl and Cd0.8Zn0.2Te) and semiconducting samples (undoped CdTe). The techniques utilized were deep level transient spectroscopy (DLTS) on semiconducting samples and photoinduced current transient spectroscopy and photo‐DLTS on high resistivity materials. These last two techniques are complementary and allow the determination of the trap character (donor/acceptor). Three acceptor levels are seen in the electrical transient data at Ev+0.12, 0.14, and 0.16 eV with hole capture cross sections of 2×10−16, 1×10−16, and 4×10−17 cm2, respectively. The lowest level is seen only in Cl doped material corroborating the literature optical and electron spin resonance identification of a level at Ev+0.12 eV as being a VCd+ClTe donor–acceptor p...

Deep levels and compensation in γ-irradiated CdZnTe

The behavior of detector-grade Cd0.9Zn0.1Te in a radiation-hostile environment has been investigated by studying the effects on the material defective states induced by γ irradiation. The detector performance is strongly affected by the presence of charge-trapping centers which may also intervene in the material compensation properties. We have investigated by photoinduced current transient spectroscopy analyses the evolution with increasing irradiation dose of the deep levels both present in the as-grown material and induced by the ionizing radiation. A significant correlation between the material resistivity and some deep levels behavior has been observed. We have compared this trend to the results obtained from γ-irradiated CdTe:Cl to better understand the role deep traps play in the compensation process of II–VI materials.

Radiation effects on II-VI compound-based detectors

The performance of room temperature CdTe and CdZnTe detectors exposed to a radiation source can be strongly altered by the interaction of the ionizing particles and the material. Up to now, few experimental data are available on the response of II–VI compound detectors to different types of radiation sources. We have carried out a thorough investigation on the effects of g-rays, neutrons and electron irradiation both on CdTe : Cl and Cd0.9Zn0.1Te detectors. We have studied the detector response after radiation exposure by means of dark current measurements and of quantitative spectroscopic analyses at low and medium energies. The deep traps present in the material have been characterized by means of PICTS (photo-induced current transient spectroscopy) analyses, which allow to determine the trap apparent activation energy and capture cross-section. The evolution of the trap parameters with increasing irradiation doses has been monitored for all the different types of radiation sources. A comparison of the results obtained for CdTe : Cl and Cd0.9Zn0.1Te detectors allows to deepen our understanding of the detectors’ properties and performance. r 2002 Elsevier Science B.V. All rights reserved.

Defective states induced in CdTe and CdZnTe detectors by high and low energy neutron irradiation

We present a study of the effects of high and low energy neutron irradiation on CdTe and CdZnTe high resistivity detector grade material. The evolution of the defect states under increasing irradiation fluence has been monitored by means of photoinduced current transient spectroscopy analyses. Particular attention is placed on the comparison and correlation between the results from the two materials under the two different neutron irradiation energies. The behavior of the observed deep traps associated with defect states allowed us to attribute an origin to most of them and to understand the role they play in the charge carrier collection process and in the degradation of material spectroscopic capabilities.

Interaction between Fe, dopants, and secondary defects in MeV Fe ion implanted InP

We investigate the role of damage production and annealing in determining the Fe redistribution properties when implanting Fe at MeV energies in n-type InP. Fe ion implantation is performed at 2 MeV on (100) InP substrates, both undoped and Sn doped (1.5×1018 cm−3). Implants are performed both at room temperature (RT) and at 200 °C (HT), with doses ranging from 1×1013 to 1.2×1015 cm−2. A double implantation experiment is also performed, coimplanting Fe and P to investigate the influence of the P induced damage on the Fe redistribution/accumulation. Annealing is performed in the temperature range between 650 and 800 °C using flowing phosphine to prevent surface decomposition. To characterize the damage of our samples before and after annealing we employ Rutherford backscattering spectrometry in channeling condition and transmission electron microscopy; Fe depth profiles are measured by secondary ions mass spectrometry. A strict correlation is found between the position of Fe accumulation peaks and that of ...

HIGH-RESISTANCE BURIED LAYERS BY MEV FE IMPLANTATION IN N-TYPE INP

We performed 2 MeV Fe implantation at a temperature of 200 °C on n-type InP substrates with different background doping concentrations. We studied the activation of Fe atoms as compensating deep acceptors and the electrical properties of the implanted layers. Simulation of the current–voltage characteristics coupled with secondary ion mass spectrometry depth profiling was used to extract important parameters such as the activated Fe fraction, the resistivity, and the thickness of the compensated layers. Our results show that resistivities of the order of 107 Ω cm can also be obtained for background doping concentrations higher than 1×1018 cm−3, with active Fe concentration well above the known solid solubility limit.

Defects introduced in cadmium telluride by γ irradiation

The properties peculiar to high resistivity CdTe:Cl are of great interest because of its application as a radiation detector. The compensation process responsible for the materials semi-insulating character implies the presence in the lattice of impurities and defects which have not yet been thoroughly characterized. The use of CdTe:Cl as a detector exposes the material to high fluxes of ionizing radiation which alter the crystal stoichiometry and affect the resulting electrical and optical properties, but few and scattered experimental data are available about radiation effects on this compound. In this work we have carried out an extensive investigation of the effects of γ irradiation on CdTe:Cl by photoinduced current transient spectroscopy analyses. We have identified the deep levels with activation energies up to midgap and we have followed their evolution with increasing irradiation doses up to 50 kGy, the dose which totally degrades the material detecting properties.

Electrical activity of deep traps in high resistivity CdTe: Spectroscopic characterization

The electrical compensation processes of high resistivity CdTe is controlled by deep levels. We have characterized the electrical activity of deep traps by means of three different and complementary spectroscopic methods: photoinduced current transient spectroscopy, surface photovoltage spectroscopy, and space charge limited current analyses. The aim is twofold: to achieve a thorough characterization of the deep trap properties and to assess the potentiality and limitations of the three experimental techniques by a cross correlation of the results obtained with each one of them. We have obtained a direct quantitative estimate of the major deep trap concentration, and we have assessed the sensitivity limit in deep-level detection for surface photovoltage spectroscopy.