Yu. M. Dikaev

Deposition of CeO2 films including areas with the different orientation and sharp border between them

Epitaxial films from one material, with sharp borders between contacting regions having different film orientation are grown on one surface of the substrate for the first time. The main reason for the deposition of thin ceria layers with mixed (001) and (111) orientations on a (1102) sapphire substrate is determined. We suggest that this is related to the availability of surface defects which, in thin near-surface layers, deviate from stoichiometric composition. This in turn is connected with the loss of oxygen. A technique for influencing CeO2 film orientation is demonstrated. This involves specific preliminary processing of the substrate, and the selection of oxygen partial pressure during the deposition process. High quality thin (30–50 nm) “protective” (001) CeO2 epitaxial layers are prepared on (1102) Al2O3. Structures comprising two epitaxial protective CeO2 layers, orientations (001) and (111), are made on the base of (0001) and (1102) sapphire substrates. The interface between the epitaxial layers is <1 000 nm. Preliminary results using this method are described, and the possibility of creating a “bi-epitaxial” transition in thin YBa2Cu3O7−x layers is explored.

On the properties of photovoltaic X-ray detectors based on GaAs epitaxial structures

Operation of a new photovoltaic detector of X-ray bremsstrahlung based on GaAs epitaxial structures at room temperature without bias is studied. The efficiency of the absorbed energy conversion into short-circuit current is calculated from the measured photoresponses for the photon energies in the range from 12 to 120 keV. In this energy range, the absorption in GaAs is governed by photoelectric effect. The efficiency of the X-ray bremsstrahlung energy conversion in GaAs peaks at 80 keV. It is suggested that the X-ray absorption of a thin 50-µm detector can be enhanced by applying an inclined irradiation scheme. The effect is most pronounced in the region of hard X-rays.

Photovoltaic X-ray detectors on the basis of GaAs epitaxial structures

The results of investigations of the properties of a new photovoltaic X-ray detector are presented. The detector was manufactured on the basis of a GaAs (p+-n-n′-n+) epitaxial structure, which was grown using the vapor-phase epitaxy method. The detector sensitivity to X-rays in a range of effective energies of 7–120 keV was measured. Multichannel linear X-ray detectors were developed and used in obtaining high-quality digital images.

Characteristics of a photovoltaic X-ray detector based on a GaAs epitaxial structure

The characteristics of a photovoltaic X-ray detector based on the GaAs p+-n-n′-n+ epitaxial structure grown using gas-phase epitaxy are studied. Typical current-voltage and capacitance-voltage characteristics of the epitaxial structures are analyzed together with the built-in electric field profile in the n-GaAs depleted region. The efficiency of charge accumulation in the photovoltaic detector is measured for zero bias and for a bias voltage of 17 V. It is shown that the GaAs-based photovoltaic X-ray detector can operate with zero bias voltage at room temperature. The sensitivity of the detector is measured as a function of the effective energy of X-rays and the angle of incidence of X-ray photons.

Reduction of the Output Ripple in X-Ray Detectors

In a multichannel X-ray detector based on epitaxial GaAs structures, a low-pass filter was used to reduce the ripple at the amplifier output. From the transient processes observed during the X-ray scanning, the optimum filter passband was determined. An X-ray source with a medium-frequency power-supply generator was used to estimate the image quality.

Multiple-pixel X-ray linear detector based on single CdZnTe crystals

The design of an X-ray linear detector based on single crystals Cd0.9Zn0.1Te has been described. The results of usage have been given.