P. Siffert

High resolution gamma ray spectroscopy with CdTe detector systems

Abstract Energy resolution and photopeak efficiency of the nowadays CdTe detector material can be improved using several detector shapes or electronic signal processing. Current results obtained in our laboratory with different detector geometries and pulse discrimination methods are presented and compared. Finally, we report on a new charge loss compensation method which improves both energy resolution and photopeak efficiency.

Preparation and Characteristics of Natural Diamond Nuclear Radiation Detectors

It is shown that natural diamond can be used as a homogeneous conduction counter with near complete charge collection, even over a long period of time. Indeed, polarization effects have been suppressed by making the back contact of the detector injecting under the influence of the applied field in order to compensate for trapped charge carriers. The electric and detection characteristics of these counters have been investigated. Possible application fields are briefly discussed.

Undoped high‐resistivity cadmium telluride for nuclear radiation detectors

Starting with highly purified feed material, single crystals of semiinsulating CdTe were grown by the use of the traveling heater method, without external chemical compensation. Evaluation of the crystals by the use of electrical and optical measurements showed decisive improvements in quality. Nuclear radiation detectors prepared by the use of this material resulted in an energy resolution (FWHM), at room temperature, of 4.6 and 8.5 keV for γ rays at energies of 122 and 662 keV, respectively. The energy resolution at 122 keV decreased to 3.8 keV at a temperature of −30°C. No polarization effect was observed.

Determination of concentration profiles by elastic recoil detection with a ΔE−E gas telescope and high energy incident heavy ions

Abstract The Elastic Recoil Detection (ERD) method has been used to determine the profile of a wide range of elements simultaneously in a thin layer (1μm) with a depth resolution of a few hundred A and high sensitivity. Z separation is achieved by a ΔE(gas)-E(solid) telescope. Results for 127I (up to 240 MeV) incident ions used to profile thin films of dielectrics (SiOxNyHz), amorphous semiconductors (a-GaAs: H) and superconductors (YBaCuO, BiSrCaCuO) are reported. It has been considered previously that ERD is of interest for analysis of light elements. We show that high energy heavy incident ions extend the field of application of the ERD method to all elements with an approximately constant depth resolution and sensitivity.

Silicon solar cells realized by laser induced diffusion of vacuum‐deposited dopants

A technique for solar cell preparation based on vacuum deposition of thin films of dopants on silicon, followed by irradiation with a high‐energy (∼1.5 J/cm2) ruby laser pulse is described. Several dopants like phosphorus, antimony, bismuth, aluminium, gallium, and indium have been investigated. Electrical and Rutherford backscattering measurements indicate that the dopant is dissolved in the silicon and becomes electrically active, as a result of the irradiation. The P‐N junctions which are formed are shallow (depth <4000 A) but heavily doped, since after the laser treatment the solubility of the dopant is generally higher than after a thermal diffusion. Therefore good diode characteristics can be achieved by this simple method, and solar cells up to 14 % efficiency under AM1 (air mass 1) illumination have been realized using dopants like phosphorus, antimony, bismuth, aluminium, or gallium.

CdTe and Cd1−xZnxTe for nuclear detectors: facts and fictions

Abstract Both CdTe and Cd 1− x Zn x Te (CZT) can be considered from their physical properties as very good materials for room temperature X- and γ-rays detection. However, despite years of intense material research, no significant advance has been made to help one to choose between both semiconductors. This paper reviews a few facts about CdTe and CZT to attempt to draw a real comparison between both. THM-CdTe and HPB-CZT have been grown and characterized in Strasbourg. Crystal growth, alloying effects, transport properties and defects are reviewed on the basis of our results and the published ones. The results show that it is still very difficult to claim which one is the best.

Temperature dependence of the reflectance of solid and liquid silicon

The reflectivity of silicon plays an important role in laser annealing. Results from literature are limited either to 225 °C in the solid phase or to 1410 °C in the liquid phase. Measurements, at 633 nm wavelength in a large temperature range near melting point, are reported here.

Structural and electrical damage induced by high‐energy heavy ions in SiO2/Si structures

The structural and electrical properties of SiO2/Si structures irradiated by high‐energy (≳0.5 GeV) Xe and Ni ions have been investigated. Structural analysis of the irradiated SiO2 films, performed with infrared spectroscopy, points to atomic displacements and broken and strained Si—O bonds induced by the irradiation. Using ir data, the damage cross section of the Xe and Ni ions has been deduced. The values are of about 8×10−13 and 6×10−14 cm2 for, respectively, 762 MeV Xe and 551 MeV Ni ions. Electrical measurements of irradiated SiO2/Si structures show an increase of the interface‐state density Dit and of the oxide trapped‐charge density N0t with the ion fluence. These results are compared with defects induced by heavy‐ion irradiation in bulk silica and by light particle radiation in silicon dioxide. Electrically active point defects have been detected in irradiated silicon and are associated with vacancy complexes.  The structural and electrical properties of SiO2/Si structures irradiated by high‐energy (≳0.5 GeV) Xe and Ni ions have been investigated. Structural analysis of the irradiated SiO2 films, performed with infrared spectroscopy, points to atomic displacements and broken and strained Si—O bonds induced by the irradiation. Using ir data, the damage cross section of the Xe and Ni ions has been deduced. The values are of about 8×10−13 and 6×10−14 cm2 for, respectively, 762 MeV Xe and 551 MeV Ni ions. Electrical measurements of irradiated SiO2/Si structures show an increase of the interface‐state density Dit and of the oxide trapped‐charge density N0t with the ion fluence. These results are compared with defects induced by heavy‐ion irradiation in bulk silica and by light particle radiation in silicon dioxide. Electrically active point defects have been detected in irradiated silicon and are associated with vacancy complexes.

Electric field distribution in CdTe and Cd1−xZnxTe nuclear detectors

Abstract Internal field measurement in nuclear radiation detectors has always been a very difficult task. Hopefully, II–VI semiconductors, and all zinc blende structure, have a strong linear electro-optical coefficient, which allows to make use of Pockels effect. CdTe and CdZnTe are IR transparent and polarized light transmission is strongly related to the internal electric field. Therefore, IR transmission provides us powerful tools for electric field mapping. Detectors with several geometry have been investigated for improving detection quality.

Phosphorus diffusion into silicon from a spin‐on source using rapid thermal processing

Diffusion of phosphorus into silicon from a doped spin‐on glass source using rapid thermal processing is described. The structural and electrical characteristics of the resulting shallow junctions including atomic and carrier concentration profiles, sheet resistance, as well as the effects on bulk carrier transport properties were studied and compared to those resulting from the use of conventional furnace heating. The results show that sheet resistance as low as 15 Ω/⧠ and surface carrier concentration higher than 1 × 1020 cm−3 are obtained in the annealed samples. Furthermore, a gettering effect is observed as the minority‐carrier diffusion length measured by the surface photovoltage technique is improved after processing.