A. Polity

Study of Hg vacancies in (Hg,Cd)Te after THM growth and post-growth annealing by positron annihilation

Positron lifetime measurements have been performed to study vacancy defects in Hg0.78Cd0.22Te. Post-growth annealing under various Hg vapour pressure conditions have been used to create a well-defined number of Hg vacancies. The sensitivity range of the positron annihilation method was found to be 1015 < cHgvac<1018 cm-3. The obtained experience has been used to investigate THM-grown single crystals. The measured longitudinal and radial dependence of the vacancy concentration can be explained by the temperature profile in the grown (Hg,Cd)Te ingots.

Determination of the defect depth profile after saw cutting of GaAs wafers measured by positron annihilation

Positron lifetime measurements and Doppler broadening spectroscopy using slow positrons were combined to investigate open-volume defects created by sawing wafers from GaAs ingots by a diamond saw cutter. It was found during step-by-step polishing that the depth distribution represents a wedgelike profile. The depth and the concentration of the defects introduced by the diamond saw depend on the advance of the saw blade. An isochronal annealing experiment was carried out to study the thermal stability of the observed defects. The positron lifetime of the dominant open-volume defect was estimated to be larger than 330 ps. It was concluded from this lifetime value and from the Doppler broadening parameters as well as from the annealing behavior that vacancy aggregates consisting of at least two vacancies are created by the sawing procedure. More extended defects such as microcracks were analyzed by scanning electron microscopy.

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 correspond well to the experimentally determined values.

Large-depth defect profiling in GaAs wafers after saw cutting

Positron lifetime measurements and Doppler-broadening spectroscopy using slow positrons were combined to investigate open-volume defects created by sawing wafers from GaAs ingots introduced by a diamond saw cutter. The depth distribution represents a large-depth (up to 9.5 μm), wedge-like profile. This was found during step-by-step etching and assembling the respective individual S(E) curves. The depth and the concentration of the defects introduced by the diamond saw depend on the advance of the saw blade. The thermal stability of the detected defects was studied by an isochronal annealing experiment. It was concluded from the positron lifetime measurements and from the Doppler-broadening parameters as well as from the annealing behavior that small vacancy aggregates consisting of at least two vacancies are created by the sawing procedure. More extended defects such as microcracks were analyzed by scanning electron microscopy (SEM). Rutherford-backscattering spectroscopy shows that there is no amorphous material in the near-surface region.

Characterization of vacancy-like defects in boron-implanted silicon with slow positrons

Abstract Vacancy-like defects in Si after boron implantation were studied by means of slow positrons. Ion implantation was carried out at 300 K subsequently with 3 energies to obtain a wide, homogeneously damaged layer. The width of the defect profiles increases with the ion dose and is in good agreement with Monte-Carlo simulations (TRIM-92). The defect production rate was ∼ N , where N is the boron fluence. This behavior is typical for defect formation via homogeneous nucleation. The divacancy concentration observed by infrared absorption was nearly constant after boron implantation, whereas the overall concentration of vacancy-like defects and the S-parameter in the implanted layer increase. This led to the conclusion that the divacancy is dominated by another defect of larger volume in highly boron-implanted Si. The samples were annealed in-situ up to 1150 K. The annealing behavior depends on the implantation dose and on the sample material (i.e. FZ- or CzSi). An annealing stage at 725 K was found in all samples. A decrease of the S-parameter below the value obtained for defect-free Si was observed in CzSi only after annealing at 750 K. This must be attributed to the formation of oxygen-vacancy complexes. An increase of the S-parameter above the defect value at room temperature was observed in a region 100 nm below the surface for high boron fluences after annealing at 650 K.

Defects in electron irradiated GaP studied by positron lifetime spectroscopy

Defects induced by electron irradiation were investigated in GaP. The irradiation was performed at 15 K with an incident electron energy of 2 MeV and a fluence of 1018cm−2. Annealing experiments were carried out in the temperature range between 100 and 1000 K.Ga and P vacancies were detected after electron irradiation and the different annealing behaviour of the two types of vacancies was observed. The recovery stage between 100 and 400 K was attributed to the annealing of Ga vacancies and the recovery at temperatures above 900 K to the annealing of P vacancies.We also performed Hall measurements to determine the location of the Fermi level in the bandgap during the annealing. Two different ionization levels of the P vacancy were found which can be attributed to the transitions VP+/VPo and VPo/VP−.Temperature-dependent measurements were performed to study the effect of shallow positron traps.