H. Bensalah

ABSTRACT The electrical and structural properties of thin metallic films (Au, Pt, or Ru) on CdZnTe (CZT) deposited by electroless deposition method have been investigated by means of Atomic Force Microscopy (AFM), Scanning Electron Microscope (SEM), Energy Dispersion X-ray (EDX), and Rutherford Backscattering Spectroscopy (RBS) measurements. SEM and AFM techniques put in evidence the modification of morphology and the change of roughness versus deposition time on the surface of contacts. The surface of Pt or Ru layer on CZT material present micro-cracks at a critical thickness, whereas it does not occur with Au layer. The thickness of Au layer with different deposition time was obtained by RBS depth profiles, which indicates a fast increase of thickness at a short deposition time and a saturation to an asymptotic value of 120 nm after 1 hour deposition.

ABSTRACT The electrical and structural properties of thin metallic layers (Au, Pt, or Ru) on CdZnTe (CZT) deposited by electroless deposition method have been investigated by means of atomic force microscopy (AFM), scanning electron microscopy (SEM), and Rutherford backscattering spectroscopy (RBS) measurements. SEM and AFM techniques put in evidence the modification of the morphology and the contact's roughness dependence with the deposition time. The surface of the Pt or Ru layer on a CZT material presents micro-cracks at a critical thickness, whereas it does not occur with the Au layer. The thickness of the Au layer with different deposition times obtained by RBS indicates first a fast increase in thickness for short deposition times and then saturation to an asymptotic value of 120 nm after 1 h.

ABSTRACT In the Bridgman and Vertical Gradient Freeze (VGF) techniques, it is common to use a high purity crucible for crystal growth. One disadvantage of pBN crucibles is associated with the crucible material interacting with the melt during the growth cycle. Using pBN crucibles for the growth of CZT, we have observed that the crucible does in fact interact with the CZT melt. To prevent this interaction, a vacuum carbon coating system for applying a carbon coating to pBN crucibles has been developed. The effects of crucible use with time are studied, as are the compositional and device properties of the bulk material. GDMS measurements are used to investigate on broron and nitrogen content, among other trace impurities found in the crystal. Devices harvested from ingots grown using cc-pBN exhibit high resistivity and good functionality as room temperature gamma ray detectors.

ABSTRACT The goal of this paper is to study the effect of superheating and fast cooling conditions on the defects of CdZnTe crystals especially Te inclusions.The paper reports characterization of the crystal defects using IR microscopy and Fourier Transform Infrared spectroscopy. Three ingots of CdZnTe doped with Indium were grown by Vertical Gradient Freezing. Ingot A and B were grown with superheating temperatures of 26 °C and 56 °C respectively. In the last case the growth process was followed by a fast cooling.The results show that the size of Te inclusions was greatly reduced and the crystal quality was improved after higher superheating and fast cooling.

ABSTRACT There are several challenges in producing detector grade material based on Cadmium Zinc Telluride (CZT), which include material synthesis and growth of electrically compensated crystals as well as the extraction of high resistivity material suitable for device applications. One of the challenges towards producing large volumes of compensated material using the Vertical Gradient Freeze (VGF) method is the axial and radial variations in material homogeneity. Growth induced strain is one of the most important factors in the crystal growth of CZT because of the low critically resolved shear stress (CRSS) value for this material. In this work, methods to reduce the thermo-mechanical stress imparted into the crystal have been implemented. Specifically, crystals have been grown under dynamic temperature gradients to minimize the temperature gradient across the ingot, while maintaining relatively higher temperature gradients at the Solid Liquid Interface (SLI). How this adjustment affects bulk resistivity and photoconductivity has been investigated.

ABSTRACT Improving the structural, optical, and electronic properties of bulk CZT remains a topic of great interest for producing high quality nuclear imaging material. The work presented here is the result of several experiments whose geometries and materials have been chosen due to their thermal properties. Results are presented for 50 mm CZT ingots grown using furnace elements which have been shown to be conducive to a convex solid–liquid interface shape. A novel crystal growth pedestal was used in this work for in-situ measurements of temperature gradients. The electrical and optical properties of the as grown material are presented. As a result, large crystal grains and volumes have been obtained for 50 mm ingots. The benefit of using this geometry has been demonstrated by comparing CZT ingots grown with and without the SiC pedestal. Gamma spectra are presented for planar devices which have been harvested from the First to Freeze regions which are most influenced by the effects of the SiC pedestal.

ABSTRACT Improving the structural, optical, and electronic properties of bulk CZT remains a topic of great interest for producing high quality nuclear imaging material. Consideration must be given to the thermal environment under which crystal growth is carried out. It is important that the furnace and insulation elements are chosen and arranged to promote a convex solid liquid interface. Results are presented for 50 mm CZT ingots grown using furnace elements, which have been shown to be conducive to a convex SLI.

ABSTRACT Despite these recent advancements in preparing the surface of Cd(Zn)Te devices for detector applications, large asymmetries in the electronic properties of planar Cd(Zn)Te detectors are common. Furthermore, for the development of patterned electrode geometries, selection of each electrode surface is crucial for minimizing dark current in the device. This investigation presented here has been carried out with three objectives. Each objective is oriented towards establishing reliable methods for the selection of the anode and cathode surfaces independent of the crystallographic orientation. The objectives of this study are (i) investigate how the asymmetry in I-V characteristics of Cd(Zn)Te devices may be associated with the TeO2 interfacial layer using Rutherford backscattering to study the structure at the Au-Cd(Zn)Te interface, (ii) develop an understanding of how the concentration of the active traps in Cd(Zn)Te varies with the external bias, and (iii) propose non-destructive methods for selection of the anode and cathode which are independent of crystallographic orientation. The spectroscopic methods employed in this investigation include Rutherford backscattering spectroscopy, photo-induced current transient spectroscopy, and surface photo-voltage spectroscopy, as well as gamma ray spectroscopy to demonstrate the influence on detector properties.

The surface quality of CdZnTe plays an important role in the performance of sensors based on this material. In this paper the effect of chemical etching on Cd0.9Zn0.1Te sensor performance was examined. Sample surfaces were treated with the same concentration 2% Br-MeOH for different etching times (30s, 2, 4, 6, 8min). The surfaces were characterized by Scanning Electron Microscopy (SEM),

ABSTRACT One of the challenges in fabricating radiation detectors based on CZT is the surface engineering for electrode deposition. Prior to electrode deposition, it is important the removal of residual contamination from the surface. Using abrasive slurries with micron and sub-micron particulates results in particle adherence to the surface, as can be readily observed using Darkfield microscopy. In addition, the wax bonding of wafers to glass plates for polishing results in further contamination as a result of solvent cleaning and inefficient wax removal in the de-bonding process.In this work, wafer mounting holders which rely upon the surface tension of a liquid are used to replace wax bonding. Using this method, detector surfaces can be prepared without the need for wax bonding and removal. As a result, the pristine nature of the surface is maintained.

In this work we study the nanopatterning effect on the surface of BIBO glasses by means of Ion Beam Sputtering (IBS), using moderate energy (<5kV) Ar ions. The analysis, changing the energy of the Ar ions, has demonstrated the formation of nanodots, nanorripples, and nanopyramids. We have also analysed the dependence of the nanopatterns on the sample thickness for the