0000000000113720
AUTHOR
S. Mäkinen
Study of vacancy defects in PbSe and Pb1-xSnxSe by positron annihilation
Abstract Positron lifetime measurements have been performed to study vacancy defects in vapour-liquid-solid (VLS) grown PbSe and Pb 1- x Sn x Se ( x = 0.07, 0.1, 0.3). Post-growth annealing under various vapour pressure conditions has been used to change the number of Pb vacancies, resulting in the determination of the specific positron trapping rate μ Pb v = (1.0±0.1)×10 14 s -1 . The sensitivity range of the positron annihilation method to the Pb vacancies was found to be 10 17 Pb ] 20 cm -3 . Positron lifetimes in perfect PbTe, PbSe and PbS crystals have been calculated. Moreover, we have predicted lifetimes of positrons trapped by vacancies. The calculated lifetimes in bulk and defects …
Hydrogen- and helium-implanted silicon: Low-temperature positron-lifetime studies
High-purity single-crystal samples of float-zoned Si have been implanted with 6.95-MeV protons and with 25-MeV {sup 3}He{sup 2} ions at 15 K, and the positron-lifetime technique has been used to identify the defects created in the samples, and to study the effects of H and He on the annealing of point defects in Si. The results have been compared with those of proton-irradiated Si. A 100--300-K annealing stage was clearly observed in hydrogen (H{sup +}) -implanted Si, and this stage was almost identical to that in the {ital p}-irradiated Si. The final annealing state of the H{sup +}-implanted Si started at about 400 K, and it is connected to annealing out of negatively charged divacancy-oxy…
Low-temperature positron-lifetime studies of proton-irradiated silicon
The positron-lifetime technique has been used to identify defects created in high-purity single-crystal silicon by irradiation with 12-MeV protons at 15 K, and the evolution of the defects has been studied by subsequent annealings between 20 and 650 K. Two clear annealing steps were seen in the samples, the first starting at 100 K and the other at 400 K. The first is suggested to be a result of the migration of free, negatively charged monovacancies, and the second is connected to the annealing of some vacancy-impurity complexes, probably negatively charged vacancy-oxygen pairs. The specific trapping rate of positrons to both of these negatively charged monovacancy-type defects has been fou…
Screening of positrons in semiconductors and insulators
Theoretical models are presented for the enhancement of the electron density at a positron in a semiconductor or insulator host. The model better suited for typical semiconductors is based on the many-body theory for the screening of a positron in electron gas. The starting point of the model for insulators is the atomic polarizability. The common parameter in both models is the high-frequency dielectric constant. Moreover, the enhancement depends on the ambient electron density in the semiconductor model and on the unit-cell volume in the insulator model. With use of the models developed, positron lifetimes in perfect semiconductor and insulator crystals have been calculated. In the calcul…
Temperature Dependence of Irradiation-Induced Magnetic Flux Loss in Nd 2 Fe 14 B Permanent Magnets
Nd2Fe14B permanent magnets were irradiated with 20 MeV protons at 300 K and at 15 K, and the flux loss was measured as a function of the irradiation dose. The results show that at 15 K the Nd2Fe14B magnets can withstand particle radiation at least 1000 times more than at room temperature.