ALBERT

Notes: Low temperature (4.2 K) photoluminescence spectroscopy (PL) measurements were performed on mercuric iodide (HgI2) crystals which were intentionally doped with copper or silver during KI etching. PL spectra obtained after these doping experiments show specific Cu and Ag features similar to those previously observed after deposition of Cu or Ag contacts on mercuric iodide crystals. The in-diffusion of Cu or Ag into bulk HgI2 has also been confirmed a few days after doping. This diffusion introduces new recombination centers in the material. This work suggests that the processing steps used to fabricate mercuric iodide nuclear detectors can lead to the introduction of new defects which are detrimental to detector performance.

Notes: We have investigated in detail (resolution up to 0.35 A(ring)) the near-band-gap 4.2 K photoluminescence spectrum of undoped Hgl2 in its red tetragonal form. At least 26 emission lines are resolved in the wavelength region between 5290 and 5400 A(ring). Many of these are reported for the first time. We have also tabulated the steplike emission lines between 5220 and 5290 A(ring).

Notes: Semitransparent palladium contacts on mercuric iodide were studied by low temperature photoluminescence spectroscopy and thermally stimulated conductivity. These contacts were deposited either by thermal evaporation or by plasma sputtering. Changes due to palladium deposition were found in the photoluminescence spectra and were attributed to modifications in the stoichiometry within the palladium/mercuric iodide interfacial region. Thermally stimulated conductivity measurements revealed two dominant traps with activation energies of 0.010 and 0.54 eV. The importance of these traps in the application of nuclear detection is discussed.

Notes: The effects of chemical etching in KI solution, heating, and vacuum exposures of HgI2 were individually studied by low-temperature photoluminescence (PL) spectroscopy. Each of these processing steps is important in the manufacturing of mercuric iodide detectors and may be responsible for the incorporation of carrier traps both in the near-surface region and in the bulk. The results of etching experiments showed that the near-surface region has a different defect structure than the bulk, which appears to result from iodine deficiency. Bulk heating at 100 °C also modifies the defect structure of the crystal. Vacuum exposure has an effect similar to chemical etching, but it does not cause significant degradation of the stoichiometry for recently KI-etched specimens. These studies suggest that some features in the PL spectra of HgI2 are associated with stoichiometry of the specimens.

Notes: The time-resolved optical reflectivity (at 633-nm wavelength) of ion-implanted silicon is measured during and immediately after CO2 laser irradiation [λ=10.6 μm, pulse duration (FWHM)=70 ns] as a function of the energy density of the laser. For a heavily doped sample and incident energy densities greater than 2.9 J/cm2, the reflectivity of the probe beam is found to rapidly jump to 70%, which is consistent with the reflectivity of liquid silicon. The high-reflectivity phase lasts for up to 1 μs, indicating a relatively deep molten layer as compared to similar annealing experiments with a visible or ultraviolet laser. The transmittance and reflectance (at 10.6-μm wavelength) of ion-implanted silicon are also reported as a function of the energy density of the CO2 laser. For energy densities slightly exceeding a threshold value, the transmittance (reflectance) of the tailing edge of the pulse is found to greatly decrease (increase). The interpretation of the optical measurements is based on a thermal model in which surface melting occurs for incident energy densities exceeding a threshold value.

Notes: A simple method is described for forming superconducting contacts to niobium thin films, as used for current perpendicular to the plane measurements of the resistance of magnetic multilayers, using an indium–Roses alloy (Bi 50/Pb 28/Sn 22) solder alloy. This solder alloy has a critical magnetic field of approximately 1.2 T. © 1997 American Institute of Physics.

Notes: Low-temperature photoluminescence (PL) spectra of detector grade Cd1−xZnxTe (x=0.1) have been measured to obtain information about shallow level defect concentration introduced during mechanical polishing and chemical etching processes. We present here a comparative PL study of Cd0.9Zn0.1Te crystals treated by different chemical solutions used for nuclear detector surface treatment. The results show that the 5% Br–MeOH+2%Br–20% lactic acid in ethylene glycol treatment combines the advantages of bromine and lactic acid for chemical etching and results in the best surface condition, as evidenced by the largest I(D0,X)/Idef intensity ratio and the narrowest full width at half-maximum of the main peak (D0,X). Changes in the surface morphology were also analyzed by atomic force microscopy and correlated with the PL results. Current–voltage (I–V) curves and the room-temperature 55Fe spectral response of the sample etched by the best treatment are also presented and discussed. © 1996 American Institute of Physics.

Notes: Specimens of mercuric iodide with evaporated semitransparent palladium contacts have been studied using low-temperature photoluminescence spectroscopy. Distinct differences were found between spectra taken from beneath the Pd contacts and those taken from regions on the HgI2 sample that were masked during the Pd deposition, indicating that contact fabrication can change the defect structure near the contact/substrate interface. Comparison of the spectra from spots beneath the contacts with spectra from bulk material specimens and HgI2 detectors graded in terms of their nuclear detection performance suggests that the processing steps used to deposit electrical contacts and the choice of contact material may have a significant influence on detector performance.

Notes: In this article we show that the behavior of new devices fabricated from horizontal Bridgman CdZnTe reported recently can be explained by the same conventional electrostatics arguments used to analyze detectors made from high pressure Bridgman material, and no qualitative differences in the material or contacts are necessary to explain the behavior of these new devices. Our work is an extension of the results obtained with a similar device geometry fabricated on high pressure Bridgman material. In addition we discuss the possibility of extending the design concepts learned here to fabricate large volume spectrometers based on a pixel array design. © 1999 American Institute of Physics.

Notes: The high-temperature diffusion of phosphorus into crystalline silicon causes the formation of electrically inactive phosphorus-rich precipitates near the surface. These precipitates decrease the carrier lifetime and mobility in the diffused layer, and thus lead to less than optimal diode characteristics of electrical junctions formed by diffusion of phosphorus into a p-type substrate. We show that the free-carrier absorption of a CO2 laser pulse can be used to completely dissolve the precipitates and remove dislocations in the diffused layer. Furthermore, we find that there are distinct advantages in depositing the pulse energy by way of free-carrier transitions, since the energy can be preferentially deposited in either confined doped layers or diffusion wells that are surrounded by lightly doped material. Our transmission electron microscopy results show that the annealing of the extended lattice defects is caused by melting of the near-surface region and subsequent liquid-phase epitaxial regrowth. Van der Pauw measurements are used to study the carrier concentration, mobility, and sheet resistivity of the samples before and after laser irradiation. The results of the electrical measurements show that there is a large increase in the carrier concentrations and a corresponding drop in the sheet resistivities of the laser irradiated samples. Using a Fourier transforminfrared spectrometer, we find that significant changes occur in the transmittance and reflectance spectra after CO2 laser annealing. Secondary ion mass spectrometry measurements are used to determine the redistribution of the phosphorus as a function of the pulse energy density. A time resolved pump-and-probe technique is utilized to measure the threshold for the onset of surface melting and the melt duration. We find that for energy densities greater than about 3 J/cm2, the reflectivity of the probe laser (at 633-nm wavelength) jumps rapidly to 70%, which is consistent with the reflectivity of liquid silicon. The interpretation of the laser induced changes in the electrical, optical, and structural properties is based on a thermal model, in which surface melting occurs for incident pulse energy densities exceeding a threshold value. Comparative calculations are reported for the melt depths and duration of surface melting, and good agreement is found. Other calculated results for the transient heating and cooling of the near-surface region are also reported.