J.P. Ponpon

Study of trapping in mercuric iodide by thermally stimulated current measurements

Thermally stimulated current measurements have been performed in red mercuric iodide crystals grown by a vapor‐phase technique. They reveal the presence of a hole trap at Ev+0.45 eV with a capture cross section of 10−15 cm2. Two additional centers were found when the crystals were cleaved rather than etched.

Optical and Optoelectric Properties of PbCdS Ternary Thin Films Deposited by CBD

Pb x Cd 1-x S films are prepared in the composition range of 0.05≤x≤0.25, using a chemical bath deposition growth technique under optimum conditions amide at realizing good photo response. The x-ray diffraction results show that the films are of PbS-CdS composite with individual CdS and PbS planes. The films exhibit two direct band gaps, 2.4 eV attributed to CdS, while the other varies continuously from 2.4 eV to 1.3 eV. The films surface morphology is smooth with crystallite, whose grain size increases with increasing mole fraction (x). The decrease in band gap with increase in lead concentration suggests inter-metallic compound of PbS (Eg=0.41 eV) with CdS (Eg=2.4 eV)

Characterization of the HgI2 surface layer after KI etching

Abstract The formation and properties of the chemical complex which forms on the HgI 2 surface during etching in KI have been investigated. The amount of complex, identified as [KHgI 3 ,H 2 O], remaining on the surface has been determined as a function of the KI concentration, the time of etching in KI and the time of rinse in water. This complex has been found to be very unstable and strongly hygroscopic. Its resistivity after drying is about 10 5 times lower than that of bulk HgI 2 .

Current instability in mercuric iodide devices

Abstract The evolution with time of the leakage current in mercuric iodide devices has been investigated. It is shown that this evolution can be closely associated with the accumulation of an electric charge which modifies the electric field in the bulk. Under particular biasing conditions, release of this charge leads to the rise of a current peak after a time delay which depends on the experimental parameters. The evolution of this peak has been investigated as a function of injected charge, voltage and temperature. As this phenomenon can be correlated with the short time behaviour of the devices, it can be used to characterize the materials devoted to the preparation of devices such as nuclear radiation detectors.

Influence of water and water vapour on the characteristics of KI treated HgI2 detectors

Abstract After being cleaned using a potassium iodide solution in water followed by a water rinse, the surface of mercuric iodide is covered by a chemical complex identified as being KHgI3·H2O. This compound can adsorb large quantities of water and its electrical properties are strongly sensitive to water and water vapour. The consequences on the manufacturing and storing conditions (especially the relative humidity), of mercuric iodide-based devices are therefore of great concern. They are illustrated by the study of the electrical and spectrometric properties of HgI2 nuclear radiation detectors.

Photoetching effects in mercuric iodide

Abstract Photoetching effects during the chemical dissolution of mercuric iodide in an iodide solution may produce noticeable surface roughening while the mean etch rate, to a first approximation, is not modified. As this phenomenon is directly related to the formation during etching of a surface chemical complex that absorbs light, the presence or not of light is an important factor in the case of KI and NH4I etching. In contrast, the surface roughness produced after HI etching is essentially light insensitive.

Systematic study of massive germanium pin diode detectors at 20 mK

Abstract To investigate the properties and improve the performances of bolometers with simultaneous measurement of ionization for dark matter search, we have realized 6 g and 70 g germanium PIN diodes with thin (35–80 nm) B and P implanted faces on 4 and 10 mm thick ultrapure germanium plates. The faces were characterized by LT sheet resistance measurements, ellipsometry, SIMS and RBS, and the bulk by carriers lifetime and capacitance measurements. We found a diode behaviour at 20 mK and 4.2 K. We made a systematic study of the response to photons from 5 to 105 keV at 0.02, 0.08 and 4.2 K, for polarization voltages from 0 to 10 V. Our main purpose was to study the slow time evolutions of the pulse heights which characterize the behaviour of such detectors at very low temperatures. We obtained a threshold of 4 keV, a resolution of 0.76 keV (rms), and a stability better than 1 hour, with a polarization voltage V = 0.2 V on a 4 mm thick diode. Similar resolutions were obtained with a 10 mm thick diode, but the time stability was worse. We found that most of the carriers are drifting across the 4 mm diode for V = 0. A possible contribution of a built-in potential to the pulses time evolution is evoked. We also studied the incomplete carriers collection close to the edges.

Recent advances in γ- and X-ray spectrometry by means of mercuric iodide detectors

Abstract Recent advances in the field of HgI2 nuclear detectors are reviewed. The main limitations of such detectors (energy range, energy resolution, stability) are discussed in view of a critical comparison between the possibilities of the material and the performance of currently available detectors. Typical results are reported to illustrate the present possibilities of these devices. Influence of the base material characteristics on the detection properties is discussed with special attention focused on trapping and polarization effects. The future evolution of HgI2 detectors and the ways to further improve the results are finally envisaged with emphasis given to low energy X- and γ-ray spectrometry and imaging.

A solid ionization chamber operated at 20 mK

Abstract We have built a germanium “solid ionization chamber” with aluminium evaporated electrodes. We obtained very low leakage current complete charge collection at 23 mK. However, we found that the spectra evolved as a function of time. To investigate this effect, the detector has been irradiated with the 43, 87, 105, and 662 keV photons of 155 Eu and 137 Cs and we analyzed this time evolution taking into account the different penetration depths of the photons. We also studied the influence of the “history” of the detector (the previous polarization voltages). We found that the electric field due to the built-in space charge (presumably induced by carriers trapping) plays an important role, and that the time evolution cannot be explained solely by the trapping of the carriers generated by each photon.

Influence of humidity on the electrical properties of potassium triiodomercurate

The electrical properties of potassium triiodomercurate crystals (KHgI3·H2O) are considerably modified in the presence of water vapour. As a result, this material presents a very high sensitivity to relative humidity (RH). Resistance changes of several orders of magnitude have been observed in triiodomercurate samples (length, cm; section, mm2) within a few tenths of second in the range 25–65% RH under a dc electric field of less than 0.5 V/cm. This behavior has been attributed to the increase of the ionic conductivity in a thin surface layer surrounding the high resistivity core of the samples. This could be induced by fast triiodomercurate dissociation in the presence of water molecules.