K. Zanio

Photoluminescence in high‐resistivity CdTe : In

Photoluminescence measurements have been performed at 4.2 K between 1.2 and 1.6 eV on compensated high‐resistivity CdTe containing from 1015 to 1018 cm−3 indium. A series of phonon‐coupled emission bands with a no‐phonon peak at 1.454 eV is dominant in most samples and grows in intensity with increasing In concentration. On the basis of the compensation model, the 1.454‐eV emission is attributed to radiative recombination at an [cadmium vacancy‐In] acceptor complex. Comparison of the experimental results with this model suggests that the chemical equilibria governing formation of the acceptor complex are frozen in at approximately 500 K as the sample is cooled from the growth temperature. The existence of significant changes at 500 K in the mobility of defects related to the acceptor complex is confirmed by the observation of a prominent growth in the 1.454‐eV emission at an annealing temperature of 500 K in A+‐implanted n‐type CdTe. Exciton emission in the CdTe : In samples is dominated by a narrow bound...

Gamma−ray spectroscopy with single−carrier collection in high−resistivity semiconductors

With the standard plane−parallel configuration of semiconductor detectors, good γ−ray spectra can only be obtained when both electrons and holes are completely collected. We show by calculations (and experiments) that with contacts of hemispherical configuration one can obtain γ−ray spectra of adequate resolution and with signal heights of nearly full amplitude even when only one type of carrier is collected. Experiments with CdTe detectors for which the μτ product for electrons is about 103 times that of the holes confirm these calculations. The adoption of hemispherical contacts thus widens the range of high−resistivity semiconductors potentially acceptable for γ−ray detection at room temperature.

Hole mobility and Poole‐Frenkel effect in CdTe

We have performed, with the time‐of‐flight technique, an extensive investigation of the transport properties of holes in high‐resistivity CdTe as a function of temperature between 130 and 430 °K and for electric fields between 5 kV/cm and 50 kV/cm. In all investigated samples, at temperatures below 300 °K, the experimental hole mobility decreases on lowering either the temperature or the electric field. These features have been interpreted on the basis of the electric field effect on trapping and detrapping phenomena (Poole‐Frenkel effect) which cause a reduction of the mobility. A critical review of the existing theories of the Poole‐Frenkel effect is presented. The Poole‐Frenkel constant obtained by comparing the experimental data with the most reliable theories of the Poole‐Frenkel effect is in excellent agreement with its theoretical value. By analysis of the experimental data it was also possible to estimate the activation energy (Et=0.14 eV) and the concentration (NT=5×1016 cm−3) of the traps which ...

Characterization of high resistivity CdTe for γ-ray detectors

Abstract This paper presents an extensive investigation on semi-insulating CdTe for use in radiation detectors. Transient techniques are used to measure the carrier drift mobilities and trapping times, the plasma time, and the activation energies, cross sections and densities of traps. A shallow electron trap with a density of 1017 cm−3, an activation energy of 0.05 ± 0.01 eV, and a cross section of 10−16 cm2 was identified. The electron trapping time increases by over an order of magnitude with increasing electric field. The plasma time for 5.48 MeV alpha particles ranged from 100 nsec at an electric field of 500 V/cm to 4 nsec at an electric field of 10 kV/cm. With 5.0 MeV alpha particles from an accelerator a room temperature resolution of 0.58% (fwhm) was obtained.

Cadmium telluride x‐ray spectrometer

The 3.9‐keV iodine Lα x‐ray line was resolved using a CdTe detector at 0 °C. A device resolution of 1.6 keV (FWHM) was obtained for the 28.6‐keV iodine Kα x‐ray line. Adverse polarization effects were not observed.

Hole Drift Velocity in Semi‐Insulating CdTe

The velocity field characteristic of holes in semi‐insulating CdTe has been measured using the time‐of‐flight technique in the space‐charge limited mode. Ohmic behavior was found up to an electric field of 35 kV/cm. The measured mobility is 70 cm2V−1 sec−1. In the course of this experiment, the hole trapping time was also measured and found to be independent of the electric field.

Analysis of CdTe as a γ‐Ray Spectrometer

Gamma spectra were taken at room temperature with devices fabricated from semi‐insulating CdTe. A resolution of 8 keV (FWHM) was found for 241Am (60 keV), 10 keV for 57Co (122 keV), 30 keV for 137Cs (662 keV), and 75 keV for 60Co (1.33 MeV). The photoelectric absorption coefficient at a photon energy of 122 keV was measured to be 5.4 ± 0.4 cm−1 in CdTe. The escape of the photoelectron at higher photon energies degraded the spectra and lowered the absorption coefficients below their theoretical values. Devices were also encapsulated within probes and their efficiency to photoelectric events was compared with that of a silicon detector. Ratios of 150:1 for 57Co and 12:1 for 241Am were found favoring CdTe.

Dependence of electron trapping time on the electric field in semi-insulating CdTe

Abstract The trapping time of electrons in semi-insulating CdTe has been measured as a function of the electric field. An increase in the applied field from 3 to 30kV /cm results in a corresponding increase in τ+ from 3 to 30 n sec.

Poole-Frenkel effect on holes in CdTe

Abstract The drift mobility of holes was measured with transient charge techniques in semi-insulating CdTe as a function of temperature and electric field. In material analyzed here the mobility was limited by multiple trapping and detrapping. The data can be explained according to the Poole-Frenkel effect on a trap with activation energy 0.150 ± 0.01 eV and a Poole-Frenkel constant 2.6 × 10−4V− 1 2 cm 1 2 eV.

InP epitaxial thin‐film formation by planar reactive deposition

Complete InP epitaxy on GaAs and twinned InP epitaxy on CdS were achieved below 390 °C by planar reactive deposition (PRD). In this technique, indium metal is evaporated from a planar source with an integral cavity into which PH3 gas is introduced and decomposed. The decomposition reaction products, P2 and H2, are emitted from within the source cavity through a perforated top plate and the combined In, P2, and H2 vapor stream on arrival at the substrate forms InP films. High‐energy electron diffraction and SEM measurements show the crystallographic quality of the resultant films to be limited by the substrate quality.