N. Baber

Simple method for direct synthesis of YBa2Cu4O8 at atmospheric oxygen pressure

A simple method for the synthesis of YBa2Cu4O8 superconductor at oxygen pressure of 1 atm is reported. The starting copper compound Cu2 (CN)2 makes it possible to synthesize near single phase material directly, without the use of reaction rate enhancers or wet chemical methods previously considered necessary. Resistivity and magnetic susceptibility measurements confirm the presence of bulk superconductivity at 81 K previously achieved only in YBa2Cu4O8 material synthesized at high oxygen pressure.

Electrical and infrared characterization of the semiconducting phases of YBa2Cu3O6+x

Abstract Semiconductivity in YBa 2 Cu 3 O 6+ x has been characterized over nearly the complete range of oxygen concentrations. Resistivity vs temperature data reveal a thermally activated conductivity with systematic variation of the activation energy with oxygen content, hitherto unreported. This suggests the existence of some acceptor-like defects which correlate with oxygen content. Infrared absorption measurements on the same samples highlight a hitherto ignored spectral feature which varies with oxygen consistent with the proposed defect picture.

Role of the mid‐gap level as the dominant recombination center in platinum doped silicon

The problem of identification of the dominant recombination center in platinum‐doped silicon is investigated using deep‐level transient spectroscopy (DLTS). Measurements using electrical and optical injection on platinum‐doped n type silicon are reported. Results of measurements show that the recently observed platinum‐related midgap level is an efficient recombination center and is probably responsible for the role of platinum as a lifetime killer. In addition, information is provided on the relative magnitudes of the electron and hole capture cross sections of the hitherto well‐known deep levels assigned to platinum.

Effects of annealing and α irradiation on deep levels in silver‐doped n‐type silicon

Deep‐level transient spectroscopy has been used to study the deep levels introduced by silver impurity in silicon. New levels in addition to the well‐known silver‐related deep donor and acceptor levels have been found. Interaction of silver‐related defects with radiation‐induced defects has been studied using α irradiation. Data on the annealing characteristics of silver‐related levels are reported. Isochronal thermal annealing before and after irradiation provides interesting insights on such interactions and on the nature of the silver‐related levels. In particular, the two newly observed prominent silver‐related levels exhibit a complementary annealing behavior, suggesting a mutual thermal transformation. The presence of silver is seen to produce a significant change in the annealing characteristics of the prominent radiation‐induced A‐center defect.

Electrical characterization of inadvertent midgap levels in GaP

Results of an electrical characterization study of two hitherto unobserved midgap deep levels in GaP using deep‐level transient spectroscopy and single‐shot dark capacitance transient techniques are reported. These are the dominant majority‐carrier (electron) levels in the green‐light‐emitting diodes studied. Detailed electron emission rate and capture cross‐section measurements are performed on these levels. The shallower of the two levels is found to have an activation energy to the conduction band varying from 0.88±0.02 eV to 0.93±0.02 eV from sample to sample while the activation energy of the deeper level is 0.96±0.02 eV. The results of the capture measurements give an upper limit of 1.2×10−19 cm2 for the electron capture cross sections of the two levels. A detailed comparison of the emission rate data with the published results on midgap levels in GaP is presented. It is proposed that one of these midgap levels may be the counterpart in GaP of the well‐known EL2 level found in GaAs.

Study of deep levels in alpha‐irradiated silver‐doped p‐type silicon

Deep‐level transient spectroscopy has been employed to study the defects in silver‐doped p‐type Si, their interaction with radiation‐induced defects, and the thermal annealing characteristics of both types of defects. The linearly graded nature of the n+p junctions used allows the acceptor (Ec−0.54 eV) and donor (Ev+0.35 eV) levels associated with silver to be studied simultaneously. The acceptor level is found to be stable against thermal annealing performed up to ∼400 °C, while the donor level shows a decrease beyond 300 °C. Important effects related with rapid thermal quenching of samples are revealed by a comparison of the data with the corresponding data on identical virgin (unquenched) samples. Irradiation by α particles leads to interesting new insights on the interaction of silver‐related defects and the radiation‐induced defects. New aspects of the kinetics and formation mechanism of the carbon‐related defects in Si are brought to light as a result of room‐temperature isothermal annealing and iso...

Interaction of α‐radiation induced defects with Pd‐related deep levels in silicon

Results of a detailed deep level transient spectroscopy study of Pd‐doped p+n Si diodes irradiated with 5.48 MeV α particles are presented, which also include investigations of isochronal annealing behavior of the deep level spectra up to a temperature of 350–400 °C. An extended comparison with results obtained on reference samples as well as with previously published results of deep level studies on Pd‐doped samples (unirradiated) and on undoped α‐irradiated samples provides valuable information, since the same starting material is used in all these studies. It is observed that, in general, the Pd‐related deep levels increase in concentration upon irradiation at the expense of α‐radiation‐induced levels. In particular, the A center sharply decreases in concentration upon post‐irradiation annealing with a corresponding increase in the concentration of the dominant Pd‐related level. The results also show that, contrary to the previously held belief, two well‐known Pd‐related levels at Ec−0.37 eV and Ec−0.5...

Field effect on thermal emission from the 0.85‐eV hole level in GaP

Results on the measurements of electric field dependence of thermal emission of holes from the 0.85‐eV level in liquid‐phase‐epitaxial GaP, using deep‐level transient spectroscopy, are reported for various temperatures. The observed field dependence is analyzed in terms of Poole–Frenkel emission from the three‐dimensional Coulomb and square‐well potentials. The field effect is found to be too weak to account for the large spread in the published emission rate data on the 0.85‐eV hole level in GaP necessitating a reappraisal of its hitherto presumed origin.

Study of the alpha irradiation and thermal annealing of gold‐doped n‐type silicon

Deep level transient spectroscopy has been used to investigate the effects of alpha irradiation and thermal annealing on deep levels in gold‐doped n‐type silicon. Data on thermal annealing characteristics of the well‐known gold acceptor up to temperatures as high as about 600 °C are reported. This level is found to be very stable, supporting the substitutional gold model for the acceptor center. Interaction of the gold‐related defects with radiation‐induced defects has been investigated using 5.48 MeV alpha particles for irradiation, combined with isochronal thermal annealing before and after irradiation. Irradiation produces the usual radiation‐induced levels. A slight reduction in the gold‐acceptor concentration is observed due to irradiation, contrary to an earlier reported study. A noticeable suppression of the thermal stability of this level is also observed after irradiation. The presence of gold leads to a significant enhancement of the anneal‐out temperature of the well‐known A‐center defect. A de...

Bleaching of the interstitial iron donor in silicon by transition metal impurities

Deep-level transient spectroscopy (DLTS) has been applied to study the interstitial iron donor (Fei) in thermally quenched p-type silicon and its interaction with some 4d and 5d transition metals. This centre is revealed by minority carrier injection in our samples with no deliberate transition metal doping. A number of its characteristics, including the emission rate signatures, its variation with thermal quenching temperature and its isothermal and isochronal annealing behaviour, have been studied to definitively identify it with the inadvertent iron impurity in our samples. A striking new property of the iron interstitial donor is revealed by our investigations on p-silicon samples doped with transition metal impurities Ag (4d), Pd (4d), Au (5d) and Pt (5d). The DLTS signal of the Fei donor is completely bleached in the presence of these impurities, leading to the suggestion that iron has a strong tendency to form complexes with these transition metal impurities.