P. Hlídek

CdTe and CdZnTe crystals for room temperature gamma-ray detectors

Abstract CdTe(Cl) detectors from CdTe single crystals, grown by the Bridgman method from Te-rich melt, were fabricated. The quality of the detectors was tested with 57Co and 241Am sources. In the 57Co spectrum low noise is demonstrated by the presence of a 14 keV peak and good resolution ≈7 keV (FWHM) evident from the separation of 122 and 136 keV peaks. A review is given of the state-of-the-art properties of (CdZn)Te single crystals prepared for substrates in the Institute of Physics of Charles University. The quality of samples is tested by measurements of the diffusion length of minority carriers, from which the mobility–lifetime product is evaluated.

Determination of energy gap in Cd1-xZnxTe (x = 0-0.06)

A dependence of energy gap on composition x for Cd1-xZnxTe (x = 0-0.06) was found combining x-ray diffraction and low temperature photoluminescence measurements (free exciton energy) on Cd1-xZnxTe single crystals. The use of this dependence for evaluation of Zn content (x) in the crystals shows very good agreement with the near infrared absorption method. Published dependences Eg(x) are reviewed and compared with the dependence Eg(x,T = 4 K) = 1.606 + 0.520x + 0.254x2 derived in this work.

RF magnetron sputtering of polymers

Abstract RF sputtering of polymeric materials such as polytetrafluoroethylene (PTFE) and polyethylene (PE) has been studied. Threshold powers of 220 and 80 W for the self-sputtering glow discharge mode were found for PTFE and PE, respectively. FTIR absorption data using polarized light disclosed a structural anisotropy of the sputtered PTFE films. A simple structural model is proposed. The first results obtained by FTIR spectroscopy of sputtered PE films are presented.

Composite Ag/C:H films prepared by DC planar magnetron deposition

Abstract Composite Ag/C:H films were deposited by means of an unbalanced magnetron operated in a gas mixture of argon and n -hexane. We used a gradual coating (‘poisoning’) of the target by a carbonaceous layer to deposit films with decreasing rate of silver sputtering. Rate of deposition of the films decreases with the covering of the magnetron target. XPS measurements were performed with the aim to study the composition of the films. The surface energy of the films was estimated from static water and formamide contact angles, which were measured using the droplet method. Values of the water contact angle were found to be in the range from 88° to 66°. Absorption spectra in the visible, near UV and IR region were studied as a function of silver concentration. FTIR spectroscopy was employed to investigate the composite films and monitor their aging. CH 2 /CH 3 stretching and deformation bands are present in all infrared spectra of the films. Evolution of the FTIR spectra with aging shows a high influence of concentration and size of the metallic inclusions on the absorption bands of the carboxyl and carbonyl groups.

Refractive index of CdTe: Spectral and temperature dependence

The refractive index of CdTe was determined from interference maxima in the transparency region from 10 to 295 K. Parameters in a four-oscillator model were fitted to experimental data and an empirical formula for the refractive index is given.

Excitonic photoluminescence in symmetric coupled double quantum wells subject to an external electric field

The effect of an external electric field F on the excitonic photoluminescence (PL) spectra of a symmetric-coupled double quantum well (DQW) is investigated both theoretically and experimentally. We show that the variational method in a two-particle electron-hole wave-function approximation gives a good agreement with measurements of PL on a narrow DQW in a wide interval of F including flat-band regime. The experimental data are presented for a molecular-beam-epitaxy\char21{}grown DQW consisting of two 5-nm-wide GaAs wells, separated by a 4-monolayers (MLs)-wide pure AlAs central barrier, and sandwiched between

Deposition of composite metal/C:H films-the basic properties of Ag/C:H

{\mathrm{Ga}}_{0.7}{\mathrm{Al}}_{0.3}\mathrm{As}

Preparation and basic physical properties of single crystals of cadmium chromium selenide CdCr2Se4

layers. The bias voltage is applied along the growth direction. Spatially direct and indirect excitonic transitions are identified, and the radius of the exciton and squeezing of the exciton in the growth direction are evaluated variationally. The excitonic binding energies, recombination energies, oscillator strengths, and relative intensities of the transitions as functions of the applied field are calculated. Our analysis demonstrates that this simple model is applicable in the case of narrow DQWs, not just for a qualitative description of the PL peak positions but also for the estimation of their individual shapes and intensities.

Electrical and luminescence properties of (CdZn)Te single crystals prepared by the vertical gradient freezing method

Abstract Composite Ag C:H films were deposited using an electromagnetron with Ag target operated in the dc unbalanced mode in a working gas mixture of n-hexane/Ar. The C:H component of this composite was investigated and its polymeric nature revealed. Structure, basic optical and dc electrical properties are described with the main emphasis on the ageing processes. A qualitative explanation is proposed.

Composite metal/C:H films prepared by unbalanced magnetron sputtering: Ni/C:H

Single crystals of CdCr2Se4 were prepared by crystallization of polycrystalline material from the melt of cadmium chloride and by synthesis from anhydrous CrCl3 and CdSe. Basic optical and transport properties were measured on the crystals. The results are compared with the available literature data and a brief survey of existing interpretation is given.