Beam-induced Defects Research Articles

A study of damage induced in semiconductors and metals during microchanneling measurements

The combination of nuclear analysis techniques and the spatial resolution obtained by microbeams is of great interest in materials characterization. The nuclear microbeam of the laboratory LARN (Namur, Belgium) has been equipped with a goniometer, allowing the use of the microchanneling technique. When using the nuclear microprobe with MeV energy helium ions in RBS channeling analysis we can produce a significant number of defects: the small beam spot size obtained with the microbeam leads to an increase of several orders of magnitude in the ion dose (ions/surface unit) required for the analysis. In this paper investigations of the defect buildup (increasing rate of dechanneling) for semiconductors (GaSb, GaAs, Si) and metals (Fe, Al, W) as a function of the total incident fluence for a 2.0 MeV focused helium microbeam (about 100 μm in diameter) are discussed. We have observed that, when the microchanneling analysis technique is used, the beam-induced defects accumulate very rapidly on compound semiconductors, but less rapidly on monoatomic samples. We have determined the evolution of χ Min values as a function of total helium beam fluences for several targets. These data can be used to estimate the highest ion dose (ions/surface unit) that is compatible with a low sample degradation during the collection of RBS spectra in channeling measurements.

In situobservations of electron irradiationdamage in magnesium

Abstract In situ electron irradiation damage has been produced in foils of magnesium of two purities (99.995% and 99.9%) in the 200 kV electron microscope. The concentration of the electron beam-induced point defect clusters in the form- of dislocation loops in the 99.9% magnesium was a factor of ten higher than that in the 99.995% material, indicating that loop nucleation and/or growth were sensitive to specimen purity. The growth kinetics of most of the dislocation loops indicated that the surfaces of the thin foils acted as dominant sinks for the electron-produced point defects. The nature of dislocation loops previously induced in magnesium by neutron irradiation was determined from their behavior under subsequent electron irradiation.

Injection-stimulated dislocation motion in semiconductors

Misfit dislocations introduced during LPE growth are shown to act as sinks for point defects introduced by 1-MeV electron bombardment in Ga1−xAlxAs1−yPy/GaAs p+n heterojunctions. Electron-beam-stimulated dislocation motion was observed directly with in situ TEM studies on previously bombarded material. SEM measurements have correlated beam-induced defect annealing with recombination-enhanced defect motion. These results suggest that dislocation networks, which are active in the dark-line-defect degradation mode of heterostructure lasers, may form by a climb mechanism which is activated by the injection-stimulated motion of point defects.

A scanning electron microscope study of the degradation of electron channelling effects in alkali halide crystals during electron irradiation

The effects ofin-situ, 25 kV electron irradiation on SEM electron channelling patterns from alkali halide crystals at room temperature are reported. Patterns were generated using wide beam and narrow beam methods. It is observed that after an initial period of irradiation, during which well defined high resolution patterns can be generated, degradation occurs. This is marked either by channelling line difiuseness or by waviness, depending on the method of generation. After prolonged irradiations, patterns can no longer be detected. Subsequent annealing experiments on irradiated NaCl show that patterns return to their original clarity if the annealing temperature is between 285 and 325‡C. Initial distortions (i.e. diffuseness and waviness) are attributed principally to the effects on the incident beam of irradiation induced surface electric fields; pattern loss, and subsequent recovery on annealing, is attributed to lattice distortion effects arising from beam-induced defect clusters.